Alcohol Use in Adolescence and Later Working Memory: Findings From a Large Population-Based Birth Cohort

PubMed Central

Field, Matt; Gage, Suzanne; Hammerton, Gemma; Heron, Jon; Hickman, Matt; Munafò, Marcus R

2018-01-01

Abstract Aims The study aimed to examine the association between adolescent alcohol use and working memory (WM) using a large population sample. Methods Data from the Avon Longitudinal Study of Parents and Children were used to investigate the association between alcohol use at age 15 years and WM 3 years later, assessed using the N-back task (N ~ 3300). A three-category ordinal variable captured mutually exclusive alcohol groupings ranging in order of severity (i.e. low alcohol users, frequent drinkers and frequent/binge drinkers). Differential dropout was accounted for using multiple imputation and inverse probability weighting. Adjustment was made for potential confounders. Results There was evidence of an association between frequent/binge drinking (compared to the low alcohol group) and poorer performance on the 3-back task after adjusting for sociodemographic confounding variables, WM at age 11 years, and experience of a head injury/unconsciousness before age 11 years (β = −0.23, 95% CI = −0.37 to −0.09, P = 0.001). However, this association was attenuated (β = −0.12, 95% CI = −0.27 to 0.03, P = 0.11) when further adjusted for baseline measures of weekly cigarette tobacco and cannabis use. Weaker associations were found for the less demanding 2-back task. We found no evidence to suggest frequent drinking was associated with performance on either task. Conclusions We found weak evidence of an association between sustained heavy alcohol use in mid-adolescence and impaired WM 3 years later. Although we cannot fully rule out the possibility of reverse causation, several potential confounding variables were included to address the directionality of the relationship between WM and alcohol use problems. PMID:29329371

The role of sex and body weight on the metabolic effects of high-fat diet in C57BL/6N mice

PubMed Central

Ingvorsen, C; Karp, N A; Lelliott, C J

2017-01-01

Background: Metabolic disorders are commonly investigated using knockout and transgenic mouse models on the C57BL/6N genetic background due to its genetic susceptibility to the deleterious metabolic effects of high-fat diet (HFD). There is growing awareness of the need to consider sex in disease progression, but limited attention has been paid to sexual dimorphism in mouse models and its impact in metabolic phenotypes. We assessed the effect of HFD and the impact of sex on metabolic variables in this strain. Methods: We generated a reference data set encompassing glucose tolerance, body composition and plasma chemistry data from 586 C57BL/6N mice fed a standard chow and 733 fed a HFD collected as part of a high-throughput phenotyping pipeline. Linear mixed model regression analysis was used in a dual analysis to assess the effect of HFD as an absolute change in phenotype, but also as a relative change accounting for the potential confounding effect of body weight. Results: HFD had a significant impact on all variables tested with an average absolute effect size of 29%. For the majority of variables (78%), the treatment effect was modified by sex and this was dominated by male-specific or a male stronger effect. On average, there was a 13.2% difference in the effect size between the male and female mice for sexually dimorphic variables. HFD led to a significant body weight phenotype (24% increase), which acts as a confounding effect on the other analysed variables. For 79% of the variables, body weight was found to be a significant source of variation, but even after accounting for this confounding effect, similar HFD-induced phenotypic changes were found to when not accounting for weight. Conclusion: HFD and sex are powerful modifiers of metabolic parameters in C57BL/6N mice. We also demonstrate the value of considering body size as a covariate to obtain a richer understanding of metabolic phenotypes. PMID:28394359

Examining the Error of Mis-Specifying Nonlinear Confounding Effect with Application on Accelerometer-Measured Physical Activity

ERIC Educational Resources Information Center

Lee, Paul H.

2017-01-01

Purpose: Some confounders are nonlinearly associated with dependent variables, but they are often adjusted using a linear term. The purpose of this study was to examine the error of mis-specifying the nonlinear confounding effect. Methods: We carried out a simulation study to investigate the effect of adjusting for a nonlinear confounder in the…

Using propensity scores to estimate the effects of insecticides on stream invertebrates from observational data

USGS Publications Warehouse

Lester L. Yuan,; Amina I. Pollard,; Carlisle, Daren M.

2009-01-01

Analyses of observational data can provide insights into relationships between environmental conditions and biological responses across a broader range of natural conditions than experimental studies, potentially complementing insights gained from experiments. However, observational data must be analyzed carefully to minimize the likelihood that confounding variables bias observed relationships. Propensity scores provide a robust approach for controlling for the effects of measured confounding variables when analyzing observational data. Here, we use propensity scores to estimate changes in mean invertebrate taxon richness in streams that have experienced insecticide concentrations that exceed aquatic life use benchmark concentrations. A simple comparison of richness in sites exposed to elevated insecticides with those that were not exposed suggests that exposed sites had on average 6.8 fewer taxa compared to unexposed sites. The presence of potential confounding variables makes it difficult to assert a causal relationship from this simple comparison. After controlling for confounding factors using propensity scores, the difference in richness between exposed and unexposed sites was reduced to 4.1 taxa, a difference that was still statistically significant. Because the propensity score analysis controlled for the effects of a wide variety of possible confounding variables, we infer that the change in richness observed in the propensity score analysis was likely caused by insecticide exposure.

Using propensity scores to estimate the effects of insecticides on stream invertebrates from observational data

USGS Publications Warehouse

Yuan, L.L.; Pollard, A.I.; Carlisle, D.M.

2009-01-01

Analyses of observational data can provide insights into relationships between environmental conditions and biological responses across a broader range of natural conditions than experimental studies, potentially complementing insights gained from experiments. However, observational data must be analyzed carefully to minimize the likelihood that confounding variables bias observed relationships. Propensity scores provide a robust approach for controlling for the effects of measured confounding variables when analyzing observational data. Here, we use propensity scores to estimate changes in mean invertebrate taxon richness in streams that have experienced insecticide concentrations that exceed aquatic life use benchmark concentrations. A simple comparison of richness in sites exposed to elevated insecticides with those that were not exposed suggests that exposed sites had on average 6.8 fewer taxa compared to unexposed sites. The presence of potential confounding variables makes it difficult to assert a causal relationship from this simple comparison. After controlling for confounding factors using propensity scores, the difference in richness between exposed and unexposed sites was reduced to 4.1 taxa, a difference that was still statistically significant. Because the propensity score analysis controlled for the effects of a wide variety of possible confounding variables, we infer that the change in richness observed in the propensity score analysis was likely caused by insecticide exposure. ?? 2009 SETAC.

A method for sensitivity analysis to assess the effects of measurement error in multiple exposure variables using external validation data.

PubMed

Agogo, George O; van der Voet, Hilko; van 't Veer, Pieter; Ferrari, Pietro; Muller, David C; Sánchez-Cantalejo, Emilio; Bamia, Christina; Braaten, Tonje; Knüppel, Sven; Johansson, Ingegerd; van Eeuwijk, Fred A; Boshuizen, Hendriek C

2016-10-13

Measurement error in self-reported dietary intakes is known to bias the association between dietary intake and a health outcome of interest such as risk of a disease. The association can be distorted further by mismeasured confounders, leading to invalid results and conclusions. It is, however, difficult to adjust for the bias in the association when there is no internal validation data. We proposed a method to adjust for the bias in the diet-disease association (hereafter, association), due to measurement error in dietary intake and a mismeasured confounder, when there is no internal validation data. The method combines prior information on the validity of the self-report instrument with the observed data to adjust for the bias in the association. We compared the proposed method with the method that ignores the confounder effect, and with the method that ignores measurement errors completely. We assessed the sensitivity of the estimates to various magnitudes of measurement error, error correlations and uncertainty in the literature-reported validation data. We applied the methods to fruits and vegetables (FV) intakes, cigarette smoking (confounder) and all-cause mortality data from the European Prospective Investigation into Cancer and Nutrition study. Using the proposed method resulted in about four times increase in the strength of association between FV intake and mortality. For weakly correlated errors, measurement error in the confounder minimally affected the hazard ratio estimate for FV intake. The effect was more pronounced for strong error correlations. The proposed method permits sensitivity analysis on measurement error structures and accounts for uncertainties in the reported validity coefficients. The method is useful in assessing the direction and quantifying the magnitude of bias in the association due to measurement errors in the confounders.

Tutorial in Biostatistics: Instrumental Variable Methods for Causal Inference*

PubMed Central

Baiocchi, Michael; Cheng, Jing; Small, Dylan S.

2014-01-01

A goal of many health studies is to determine the causal effect of a treatment or intervention on health outcomes. Often, it is not ethically or practically possible to conduct a perfectly randomized experiment and instead an observational study must be used. A major challenge to the validity of observational studies is the possibility of unmeasured confounding (i.e., unmeasured ways in which the treatment and control groups differ before treatment administration which also affect the outcome). Instrumental variables analysis is a method for controlling for unmeasured confounding. This type of analysis requires the measurement of a valid instrumental variable, which is a variable that (i) is independent of the unmeasured confounding; (ii) affects the treatment; and (iii) affects the outcome only indirectly through its effect on the treatment. This tutorial discusses the types of causal effects that can be estimated by instrumental variables analysis; the assumptions needed for instrumental variables analysis to provide valid estimates of causal effects and sensitivity analysis for those assumptions; methods of estimation of causal effects using instrumental variables; and sources of instrumental variables in health studies. PMID:24599889

Evaluation of uncontrolled confounding in studies of environmental exposures and neurobehavioral testing in children.

PubMed

Mink, Pamela J; Goodman, Michael; Barraj, Leila M; Imrey, Harriet; Kelsh, Michael A; Yager, Janice

2004-07-01

Neurobehavioral tests are commonly used in studies of children exposed to low-level environmental concentrations of compounds known to be neurotoxic at higher levels. However, uncontrolled or incomplete control for confounding makes interpretation of results problematic because effects of confounders are often stronger than the effects of primary interest. We examined a priori the potential impact of confounding in a hypothetical study evaluating the association of a potentially neurotoxic environmental exposure with neurobehavioral function in children. We used 2 outcome measures: the Bayley Scales of Infant Development Mental Development Index and the Stanford-Binet Intelligence Scale Composite Score. We selected 3 potential confounders: maternal intelligence, home environment, and socioeconomic status as measured by years of parental education. We conducted 3 sets of analyses measuring the effect of each of the 3 confounding factors alone, 2 confounders acting simultaneously, and all 3 confounders acting simultaneously. Relatively small differences (0.5 standard deviations) in confounding variables between "exposed" and "unexposed" groups, if unmeasured and unaccounted for in the analysis, could produce spurious differences in cognitive test scores. The magnitude of this difference (3-10 points) has been suggested to have a meaningful impact in populations. The method of measuring confounders (eg, maternal intelligence) could also substantially affect the results. It is important to carefully consider the impact of potential confounders during the planning stages of an observational study. Study-to-study differences in neurobehavioral outcomes with similar environmental exposures could be partially explained by differences in the adjustment for confounding variables. Copyright 2004 Lippincott Williams and Wilkins

Factors Associated with Hepatitis C Knowledge Before and After an Educational Intervention among Vietnamese Americans

PubMed Central

Lee, Sunmin; Zhai, Shumenghui; Zhang, Guo (Yolanda); Ma, Xiang S; Lu, Xiaoxiao; Tan, Yin; Siu, Philip; Seals, Brenda; Ma, Grace X

2015-01-01

BACKGROUND Hepatitis C virus (HCV) is a major cause of chronic liver disease and cancer. Vietnamese Americans are at high risk of HCV infection, with men having the highest US incidence of liver cancer. This study examines an intervention to improve HCV knowledge among Vietnamese Americans. STUDY Seven Vietnamese community-based organizations in Pennsylvania and New Jersey recruited a total of 306 Vietnamese participants from 2010 to 2011. RESULTS Average knowledge scores for pretest and posttest were 3.32 and 5.88, respectively (maximum 10). After adjusting for confounding variables, age and higher education were positively associated with higher pretest scores and having a physician who spoke English or Vietnamese was negatively associated with higher pretest scores. Additionally, after adjusting for confounding variables, household income, education, and having an HCV-infected family member significantly increased knowledge scores. CONCLUSIONS Promotion and development of HCV educational programs can increase HCV knowledge among race and ethnic groups, such as Vietnamese Americans. Giving timely information to at-risk groups provides the opportunity to correct misconceptions, decrease HCV risk behaviors, and encourage testing that might improve timely HCV diagnosis and treatment. PMID:26561280

Interpretational confounding is due to misspecification, not to type of indicator: comment on Howell, Breivik, and Wilcox (2007).

PubMed

Bollen, Kenneth A

2007-06-01

R. D. Howell, E. Breivik, and J. B. Wilcox (2007) have argued that causal (formative) indicators are inherently subject to interpretational confounding. That is, they have argued that using causal (formative) indicators leads the empirical meaning of a latent variable to be other than that assigned to it by a researcher. Their critique of causal (formative) indicators rests on several claims: (a) A latent variable exists apart from the model when there are effect (reflective) indicators but not when there are causal (formative) indicators, (b) causal (formative) indicators need not have the same consequences, (c) causal (formative) indicators are inherently subject to interpretational confounding, and (d) a researcher cannot detect interpretational confounding when using causal (formative) indicators. This article shows that each claim is false. Rather, interpretational confounding is more a problem of structural misspecification of a model combined with an underidentified model that leaves these misspecifications undetected. Interpretational confounding does not occur if the model is correctly specified whether a researcher has causal (formative) or effect (reflective) indicators. It is the validity of a model not the type of indicator that determines the potential for interpretational confounding. Copyright 2007 APA, all rights reserved.

Prenatal Maternal Stress Associated with ADHD and Autistic Traits in early Childhood

PubMed Central

Ronald, Angelica; Pennell, Craig E.; Whitehouse, Andrew J. O.

2010-01-01

Research suggests that offspring of mothers who experience high levels of stress during pregnancy are more likely to have problems in neurobehavioral development. There is preliminary evidence that prenatal maternal stress (PNMS) is a risk factor for both autism and attention deficit hyperactivity disorder (ADHD), however most studies do not control for confounding factors and no study has investigated PNMS as a risk factor for behaviors characteristic of these disorders in early childhood. A population cohort of 2900 pregnant women were recruited before their 18th week of pregnancy and investigated prospectively. Maternal experience of stressful life events was assessed during pregnancy. When offspring were age 2 years, mothers completed the child behavior checklist. Multiple regression showed that maternal stressful events during pregnancy significantly predicted ADHD behaviors in offspring, after controlling for autistic traits and other confounding variables, in both males (p = 0.03) and females (p = 0.01). Similarly, stressful events during pregnancy significantly predicted autistic traits in the offspring after controlling for ADHD behaviors and confounding variables, in males only (p = 0.04). In conclusion, this study suggests that PNMS, in the form of typical stressful life events such as divorce or a residential move, show a small but significant association with both autistic traits and ADHD behaviors independently, in offspring at age 2 years, after controlling for multiple antenatal, obstetric, postnatal, and sociodemographic covariates. This finding supports future research using epigenetic, cross-fostering, and gene–environment interaction designs to identify the causal processes underlying this association. PMID:21833278

Intra-Aortic Balloon Pump Counterpulsation during Primary Percutaneous Coronary Intervention for ST-Elevation Myocardial Infarction and Cardiogenic Shock: Insights from the British Columbia Cardiac Registry

PubMed Central

Iqbal, M. Bilal; Robinson, Simon D.; Ding, Lillian; Fung, Anthony; Aymong, Eve; Chan, Albert W.; Hodge, Steven; Della Siega, Anthony; Nadra, Imad J.

2016-01-01

Background Cardiogenic shock complicating ST-elevation myocardial infarction (STEMI) is associated with significant morbidity and mortality. In the primary percutaneous coronary intervention (PPCI) era, randomized trials have not shown a survival benefit with intra-aortic balloon pump (IABP) therapy. This differs to observational data which show a detrimental effect, potentially reflecting bias and confounding. Without robust and valid risk adjustment, findings from non-randomized studies may remain biased. Methods We compared long-term mortality following IABP therapy in patients with cardiogenic shock undergoing PPCI during 2008–2013 from the British Columbia Cardiac Registry. We addressed measured and unmeasured confounding using propensity score and instrumental variable methods. Results A total of 12,105 patients with STEMI were treated with PPCI during the study period. Of these, 700 patients (5.8%) had cardiogenic shock. Of the patients with cardiogenic shock, 255 patients (36%) received IABP therapy. Multivariable analyses identified IABP therapy to be associated with increased mortality up to 3 years (HR = 1.67, 95% CI:1.20–2.67, p<0.001). This association was lost in propensity-matched analyses (HR = 1.23, 95% CI: 0.84–1.80, p = 0.288). When addressing measured and unmeasured confounders, instrumental variable analyses demonstrated that IABP therapy was not associated with mortality at 3 years (Δ = 16.7%, 95% CI: -12.7%, 46.1%, p = 0.281). Subgroup analyses demonstrated IABP was associated with increased mortality in non-diabetics; patients not undergoing multivessel intervention; patients without renal disease and patients not having received prior thrombolysis. Conclusions In this observational analysis of patients with STEMI and cardiogenic shock, when adjusting for confounding, IABP therapy had a neutral effect with no association with long-term mortality. These findings differ to previously reported observational studies, but are in keeping with randomized trial data. PMID:26870950

Assessing the Independent Contribution of Maternal Educational Expectations to Children’s Educational Attainment in Early Adulthood: A Propensity Score Matching Analysis

PubMed Central

Pingault, Jean Baptiste; Côté, Sylvana M.; Petitclerc, Amélie; Vitaro, Frank; Tremblay, Richard E.

2015-01-01

Background Parental educational expectations have been associated with children’s educational attainment in a number of long-term longitudinal studies, but whether this relationship is causal has long been debated. The aims of this prospective study were twofold: 1) test whether low maternal educational expectations contributed to failure to graduate from high school; and 2) compare the results obtained using different strategies for accounting for confounding variables (i.e. multivariate regression and propensity score matching). Methodology/Principal Findings The study sample included 1,279 participants from the Quebec Longitudinal Study of Kindergarten Children. Maternal educational expectations were assessed when the participants were aged 12 years. High school graduation – measuring educational attainment – was determined through the Quebec Ministry of Education when the participants were aged 22–23 years. Findings show that when using the most common statistical approach (i.e. multivariate regressions to adjust for a restricted set of potential confounders) the contribution of low maternal educational expectations to failure to graduate from high school was statistically significant. However, when using propensity score matching, the contribution of maternal expectations was reduced and remained statistically significant only for males. Conclusions/Significance The results of this study are consistent with the possibility that the contribution of parental expectations to educational attainment is overestimated in the available literature. This may be explained by the use of a restricted range of potential confounding variables as well as the dearth of studies using appropriate statistical techniques and study designs in order to minimize confounding. Each of these techniques and designs, including propensity score matching, has its strengths and limitations: A more comprehensive understanding of the causal role of parental expectations will stem from a convergence of findings from studies using different techniques and designs. PMID:25803867

Instrumental Variable Methods for Continuous Outcomes That Accommodate Nonignorable Missing Baseline Values.

PubMed

Ertefaie, Ashkan; Flory, James H; Hennessy, Sean; Small, Dylan S

2017-06-15

Instrumental variable (IV) methods provide unbiased treatment effect estimation in the presence of unmeasured confounders under certain assumptions. To provide valid estimates of treatment effect, treatment effect confounders that are associated with the IV (IV-confounders) must be included in the analysis, and not including observations with missing values may lead to bias. Missing covariate data are particularly problematic when the probability that a value is missing is related to the value itself, which is known as nonignorable missingness. In such cases, imputation-based methods are biased. Using health-care provider preference as an IV method, we propose a 2-step procedure with which to estimate a valid treatment effect in the presence of baseline variables with nonignorable missing values. First, the provider preference IV value is estimated by performing a complete-case analysis using a random-effects model that includes IV-confounders. Second, the treatment effect is estimated using a 2-stage least squares IV approach that excludes IV-confounders with missing values. Simulation results are presented, and the method is applied to an analysis comparing the effects of sulfonylureas versus metformin on body mass index, where the variables baseline body mass index and glycosylated hemoglobin have missing values. Our result supports the association of sulfonylureas with weight gain. © The Author 2017. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Adult Lifespan Cognitive Variability in the Cross-Sectional Cam-CAN Cohort

PubMed Central

Green, Emma; Shafto, Meredith A.; Matthews, Fiona E.; White, Simon R.

2015-01-01

This study examines variability across the age span in cognitive performance in a cross-sectional, population-based, adult lifespan cohort from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) study (n = 2680). A key question we highlight is whether using measures that are designed to detect age-related cognitive pathology may not be sensitive to, or reflective of, individual variability among younger adults. We present three issues that contribute to the debate for and against age-related increases in variability. Firstly, the need to formally define measures of central tendency and measures of variability. Secondly, in addition to the commonly addressed location-confounding (adjusting for covariates) there may exist changes in measures of variability due to confounder sub-groups. Finally, that increases in spread may be a result of floor or ceiling effects; where the measure is not sensitive enough at all ages. From the Cam-CAN study, a large population-based dataset, we demonstrate the existence of variability-confounding for the immediate episodic memory task; and show that increasing variance with age in our general cognitive measures is driven by a ceiling effect in younger age groups. PMID:26690191

Adult Lifespan Cognitive Variability in the Cross-Sectional Cam-CAN Cohort.

PubMed

Green, Emma; Shafto, Meredith A; Matthews, Fiona E; White, Simon R

2015-12-07

This study examines variability across the age span in cognitive performance in a cross-sectional, population-based, adult lifespan cohort from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) study (n = 2680). A key question we highlight is whether using measures that are designed to detect age-related cognitive pathology may not be sensitive to, or reflective of, individual variability among younger adults. We present three issues that contribute to the debate for and against age-related increases in variability. Firstly, the need to formally define measures of central tendency and measures of variability. Secondly, in addition to the commonly addressed location-confounding (adjusting for covariates) there may exist changes in measures of variability due to confounder sub-groups. Finally, that increases in spread may be a result of floor or ceiling effects; where the measure is not sensitive enough at all ages. From the Cam-CAN study, a large population-based dataset, we demonstrate the existence of variability-confounding for the immediate episodic memory task; and show that increasing variance with age in our general cognitive measures is driven by a ceiling effect in younger age groups.

Supervisor Autonomy and Considerate Leadership Style are Associated with Supervisors’ Likelihood to Accommodate Back Injured Workers

PubMed Central

McGuire, Connor; Kristman, Vicki L; Williams-Whitt, Kelly; Reguly, Paula; Shaw, William; Soklaridis, Sophie

2015-01-01

PURPOSE To determine the association between supervisors’ leadership style and autonomy and supervisors’ likelihood of supporting job accommodations for back-injured workers. METHODS A cross-sectional study of supervisors from Canadian and US employers was conducted using a web-based, self-report questionnaire that included a case vignette of a back-injured worker. Autonomy and two dimensions of leadership style (considerate and initiating structure) were included as exposures. The outcome, supervisors’ likeliness to support job accommodation, was measured with the Job Accommodation Scale. We conducted univariate analyses of all variables and bivariate analyses of the JAS score with each exposure and potential confounding factor. We used multivariable generalized linear models to control for confounding factors. RESULTS A total of 796 supervisors participated. Considerate leadership style (β= .012; 95% CI: .009–.016) and autonomy (β= .066; 95% CI: .025–.11) were positively associated with supervisors’ likelihood to accommodate after adjusting for appropriate confounding factors. An initiating structure leadership style was not significantly associated with supervisors’ likelihood to accommodate (β = .0018; 95% CI: −.0026–.0061) after adjusting for appropriate confounders. CONCLUSIONS Autonomy and a considerate leadership style were positively associated with supervisors’ likelihood to accommodate a back-injured worker. Providing supervisors with more autonomy over decisions of accommodation and developing their considerate leadership style may aid in increasing work accommodation for back-injured workers and preventing prolonged work disability. PMID:25595332

Using instrumental variables to estimate a Cox's proportional hazards regression subject to additive confounding

PubMed Central

Tosteson, Tor D.; Morden, Nancy E.; Stukel, Therese A.; O'Malley, A. James

2014-01-01

The estimation of treatment effects is one of the primary goals of statistics in medicine. Estimation based on observational studies is subject to confounding. Statistical methods for controlling bias due to confounding include regression adjustment, propensity scores and inverse probability weighted estimators. These methods require that all confounders are recorded in the data. The method of instrumental variables (IVs) can eliminate bias in observational studies even in the absence of information on confounders. We propose a method for integrating IVs within the framework of Cox's proportional hazards model and demonstrate the conditions under which it recovers the causal effect of treatment. The methodology is based on the approximate orthogonality of an instrument with unobserved confounders among those at risk. We derive an estimator as the solution to an estimating equation that resembles the score equation of the partial likelihood in much the same way as the traditional IV estimator resembles the normal equations. To justify this IV estimator for a Cox model we perform simulations to evaluate its operating characteristics. Finally, we apply the estimator to an observational study of the effect of coronary catheterization on survival. PMID:25506259

Using instrumental variables to estimate a Cox's proportional hazards regression subject to additive confounding.

PubMed

MacKenzie, Todd A; Tosteson, Tor D; Morden, Nancy E; Stukel, Therese A; O'Malley, A James

2014-06-01

The estimation of treatment effects is one of the primary goals of statistics in medicine. Estimation based on observational studies is subject to confounding. Statistical methods for controlling bias due to confounding include regression adjustment, propensity scores and inverse probability weighted estimators. These methods require that all confounders are recorded in the data. The method of instrumental variables (IVs) can eliminate bias in observational studies even in the absence of information on confounders. We propose a method for integrating IVs within the framework of Cox's proportional hazards model and demonstrate the conditions under which it recovers the causal effect of treatment. The methodology is based on the approximate orthogonality of an instrument with unobserved confounders among those at risk. We derive an estimator as the solution to an estimating equation that resembles the score equation of the partial likelihood in much the same way as the traditional IV estimator resembles the normal equations. To justify this IV estimator for a Cox model we perform simulations to evaluate its operating characteristics. Finally, we apply the estimator to an observational study of the effect of coronary catheterization on survival.

The Problem of Confounding in Studies of the Effect of Maternal Drug Use on Pregnancy Outcome

PubMed Central

Källén, Bengt

2012-01-01

In most epidemilogical studies, the problem of confounding adds to the uncertainty in conclusions drawn. This is also true for studies on the effect of maternal drug use on birth defect risks. This paper describes various types of such confounders and discusses methods to identify and adjust for them. Such confounders can be found in maternal characteristics like age, parity, smoking, use of alcohol, and body mass index, subfertility, and previous pregnancies including previous birth of a malformed child, socioeconomy, race/ethnicity, or country of birth. Confounding by concomitant maternal drug use may occur. A geographical or seasonal confounding can exist. In rare instances, infant sex and multiple birth can appear as confounders. The most difficult problem to solve is often confounding by indication. The problem of confounding is less important for congenital malformations than for many other pregnancy outcomes. PMID:22190949

Effect of Breastfeeding on Head Circumference of Children from Impoverished Communities

PubMed Central

Xavier Júnior, Antonio Fernando Silva; de Assunção, Monica Lopes; dos Santos, Ewerton Amorim; Horta, Bernardo Lessa

2013-01-01

Abstract Objective This study investigated the effect of exclusive breastfeeding on head circumference (HC) among children living in impoverished communities. Subjects and Methods A cross-sectional study was conducted among children 12–60 months old from the 39 quilombos located in the State of Alagoas, Brazil. HC deficit was defined by a z-score of less than −2 from the median (based on the 2006 World Health Organization growth standards). Prevalence ratio and 95% confidence interval (95% CI) were estimated using Poisson regression with robust adjustment of the variance, and estimates were adjusted for possible confounders (anthropometric, socioeconomic, demographic, and health-related variables). Results We evaluated 725 children (365 boys and 360 girls). The prevalence of HC deficit was 13.3% among those children who were exclusively breastfed for less than 30 days, 10.6% among those exclusively breastfed for 30–119 days, and 5.8% among those who were exclusively breastfed for 120 days or more. Even after controlling for possible confounding variables, exclusive breastfeeding for ≥4 months decreased the risk of HC deficit (prevalence ratio, 0.48; 95% CI 0.24, 0.99). Conclusions Exclusive breastfeeding for ≥4 months was associated with a larger HC in children exposed to great social vulnerability in impoverished communities. PMID:23414229

Napping during the night shift and recovery after work among hospital nurses1

PubMed Central

Palermo, Thaís Aparecida de Castro; Rotenberg, Lúcia; Zeitoune, Regina Célia Gollner; Silva-Costa, Aline; Souto, Ester Paiva; Griep, Rosane Härter

2015-01-01

OBJECTIVE: To analyze the association between the length of napping during the night shift and the recovery after work among nurses. METHOD: Cross-sectional epidemiological study involving 1940 nurses from 18 public hospitals in the City of Rio de Janeiro. A multidimensional and self-applied questionnaire was used with information about health, sociodemographic and occupational characteristics, health-related behaviors and housework. Multiple logistic regression was applied to identify the association, adjusted for confounding variables. RESULTS: The gross analyses showed 44%, 127% and 66% higher chances of a high level of recovery after work for nurses who sleep up to two hours, between 2.1 and 3 hours and 3.1 hours or more, respectively, when compared to the nurses who do not sleep. After adjusting for confounding variables, the association only continues significant for the group that sleeps 2.1 to 3 hours during the night shift (OR=1.79; 95%CI=1.33-2.41). CONCLUSION: The association between the length of napping and the high level of recovery after work, confirmed in the present results, can be included in the studies that aim to support more appropriate policies aimed at improving the workers' work, life and health conditions, not only in nursing, but night-shift workers in general. PMID:25806639

Quasi-experimental study designs series-paper 9: collecting data from quasi-experimental studies.

PubMed

Aloe, Ariel M; Becker, Betsy Jane; Duvendack, Maren; Valentine, Jeffrey C; Shemilt, Ian; Waddington, Hugh

2017-09-01

To identify variables that must be coded when synthesizing primary studies that use quasi-experimental designs. All quasi-experimental (QE) designs. When designing a systematic review of QE studies, potential sources of heterogeneity-both theory-based and methodological-must be identified. We outline key components of inclusion criteria for syntheses of quasi-experimental studies. We provide recommendations for coding content-relevant and methodological variables and outlined the distinction between bivariate effect sizes and partial (i.e., adjusted) effect sizes. Designs used and controls used are viewed as of greatest importance. Potential sources of bias and confounding are also addressed. Careful consideration must be given to inclusion criteria and the coding of theoretical and methodological variables during the design phase of a synthesis of quasi-experimental studies. The success of the meta-regression analysis relies on the data available to the meta-analyst. Omission of critical moderator variables (i.e., effect modifiers) will undermine the conclusions of a meta-analysis. Copyright © 2017 Elsevier Inc. All rights reserved.

Bayesian effect estimation accounting for adjustment uncertainty.

PubMed

Wang, Chi; Parmigiani, Giovanni; Dominici, Francesca

2012-09-01

Model-based estimation of the effect of an exposure on an outcome is generally sensitive to the choice of which confounding factors are included in the model. We propose a new approach, which we call Bayesian adjustment for confounding (BAC), to estimate the effect of an exposure of interest on the outcome, while accounting for the uncertainty in the choice of confounders. Our approach is based on specifying two models: (1) the outcome as a function of the exposure and the potential confounders (the outcome model); and (2) the exposure as a function of the potential confounders (the exposure model). We consider Bayesian variable selection on both models and link the two by introducing a dependence parameter, ω, denoting the prior odds of including a predictor in the outcome model, given that the same predictor is in the exposure model. In the absence of dependence (ω= 1), BAC reduces to traditional Bayesian model averaging (BMA). In simulation studies, we show that BAC, with ω > 1, estimates the exposure effect with smaller bias than traditional BMA, and improved coverage. We, then, compare BAC, a recent approach of Crainiceanu, Dominici, and Parmigiani (2008, Biometrika 95, 635-651), and traditional BMA in a time series data set of hospital admissions, air pollution levels, and weather variables in Nassau, NY for the period 1999-2005. Using each approach, we estimate the short-term effects of on emergency admissions for cardiovascular diseases, accounting for confounding. This application illustrates the potentially significant pitfalls of misusing variable selection methods in the context of adjustment uncertainty. © 2012, The International Biometric Society.

Combating Unmeasured Confounding in Cross-Sectional Studies: Evaluating Instrumental-Variable and Heckman Selection Models

PubMed Central

DeMaris, Alfred

2014-01-01

Unmeasured confounding is the principal threat to unbiased estimation of treatment “effects” (i.e., regression parameters for binary regressors) in nonexperimental research. It refers to unmeasured characteristics of individuals that lead them both to be in a particular “treatment” category and to register higher or lower values than others on a response variable. In this article, I introduce readers to 2 econometric techniques designed to control the problem, with a particular emphasis on the Heckman selection model (HSM). Both techniques can be used with only cross-sectional data. Using a Monte Carlo experiment, I compare the performance of instrumental-variable regression (IVR) and HSM to that of ordinary least squares (OLS) under conditions with treatment and unmeasured confounding both present and absent. I find HSM generally to outperform IVR with respect to mean-square-error of treatment estimates, as well as power for detecting either a treatment effect or unobserved confounding. However, both HSM and IVR require a large sample to be fully effective. The use of HSM and IVR in tandem with OLS to untangle unobserved confounding bias in cross-sectional data is further demonstrated with an empirical application. Using data from the 2006–2010 General Social Survey (National Opinion Research Center, 2014), I examine the association between being married and subjective well-being. PMID:25110904

Nonlinear Predictive Models for Multiple Mediation Analysis: With an Application to Explore Ethnic Disparities in Anxiety and Depression Among Cancer Survivors.

PubMed

Yu, Qingzhao; Medeiros, Kaelen L; Wu, Xiaocheng; Jensen, Roxanne E

2018-04-02

Mediation analysis allows the examination of effects of a third variable (mediator/confounder) in the causal pathway between an exposure and an outcome. The general multiple mediation analysis method (MMA), proposed by Yu et al., improves traditional methods (e.g., estimation of natural and controlled direct effects) to enable consideration of multiple mediators/confounders simultaneously and the use of linear and nonlinear predictive models for estimating mediation/confounding effects. Previous studies find that compared with non-Hispanic cancer survivors, Hispanic survivors are more likely to endure anxiety and depression after cancer diagnoses. In this paper, we applied MMA on MY-Health study to identify mediators/confounders and quantify the indirect effect of each identified mediator/confounder in explaining ethnic disparities in anxiety and depression among cancer survivors who enrolled in the study. We considered a number of socio-demographic variables, tumor characteristics, and treatment factors as potential mediators/confounders and found that most of the ethnic differences in anxiety or depression between Hispanic and non-Hispanic white cancer survivors were explained by younger diagnosis age, lower education level, lower proportions of employment, less likely of being born in the USA, less insurance, and less social support among Hispanic patients.

Instrumental variables as bias amplifiers with general outcome and confounding.

PubMed

Ding, P; VanderWeele, T J; Robins, J M

2017-06-01

Drawing causal inference with observational studies is the central pillar of many disciplines. One sufficient condition for identifying the causal effect is that the treatment-outcome relationship is unconfounded conditional on the observed covariates. It is often believed that the more covariates we condition on, the more plausible this unconfoundedness assumption is. This belief has had a huge impact on practical causal inference, suggesting that we should adjust for all pretreatment covariates. However, when there is unmeasured confounding between the treatment and outcome, estimators adjusting for some pretreatment covariate might have greater bias than estimators without adjusting for this covariate. This kind of covariate is called a bias amplifier, and includes instrumental variables that are independent of the confounder, and affect the outcome only through the treatment. Previously, theoretical results for this phenomenon have been established only for linear models. We fill in this gap in the literature by providing a general theory, showing that this phenomenon happens under a wide class of models satisfying certain monotonicity assumptions. We further show that when the treatment follows an additive or multiplicative model conditional on the instrumental variable and the confounder, these monotonicity assumptions can be interpreted as the signs of the arrows of the causal diagrams.

Poppers, Kaposi's sarcoma, and HIV infection: empirical example of a strong confounding effect?

PubMed

Morabia, A

1995-01-01

Are there empirical examples of strong confounding effects? Textbooks usually show examples of weak confounding or use hypothetical examples of strong confounding to illustrate the paradoxical consequences of not separating out the effect of the studied exposure from that of second factor acting as a confounder. HIV infection is a candidate strong confounder of the spuriously high association reported between consumption of poppers, a sexual stimulant, and risk of Kaposi's sarcoma in the early phase of the AIDS epidemic. To examine this hypothesis, assumptions must be made on the prevalence of HIV infection among cases of Kaposi's sarcoma and on the prevalence of heavy popper consumption according to HIV infection in cases and controls. Results show that HIV infection may have confounded the poppers-Kaposi's sarcoma association. However, it cannot be ruled out that HIV did not qualify as a confounder because it was either an intermediate variable or an effect modifier of the association between popper inhalation and Kaposi's sarcoma. This example provides a basis to discuss the mechanism by which confounding occurs as well as the practical importance of confounding in epidemiologic research.

Relation between sick leave and selected exposure variables among women semiconductor workers in Malaysia

PubMed Central

Chee, H; Rampal, K

2003-01-01

Aims: To determine the relation between sick leave and selected exposure variables among women semiconductor workers. Methods: This was a cross sectional survey of production workers from 18 semiconductor factories. Those selected had to be women, direct production operators up to the level of line leader, and Malaysian citizens. Sick leave and exposure to physical and chemical hazards were determined by self reporting. Three sick leave variables were used; number of sick leave days taken in the past year was the variable of interest in logistic regression models where the effects of age, marital status, work task, work schedule, work section, and duration of work in factory and work section were also explored. Results: Marital status was strongly linked to the taking of sick leave. Age, work schedule, and duration of work in the factory were significant confounders only in certain cases. After adjusting for these confounders, chemical and physical exposures, with the exception of poor ventilation and smelling chemicals, showed no significant relation to the taking of sick leave within the past year. Work section was a good predictor for taking sick leave, as wafer polishing workers faced higher odds of taking sick leave for each of the three cut off points of seven days, three days, and not at all, while parts assembly workers also faced significantly higher odds of taking sick leave. Conclusion: In Malaysia, the wafer fabrication factories only carry out a limited portion of the work processes, in particular, wafer polishing and the processes immediately prior to and following it. This study, in showing higher illness rates for workers in wafer polishing compared to semiconductor assembly, has implications for the governmental policy of encouraging the setting up of wafer fabrication plants with the full range of work processes. PMID:12660374

An overview of confounding. Part 1: the concept and how to address it.

PubMed

Howards, Penelope P

2018-04-01

Confounding is an important source of bias, but it is often misunderstood. We consider how confounding occurs and how to address confounding using examples. Study results are confounded when the effect of the exposure on the outcome, mixes with the effects of other risk and protective factors for the outcome. This problem arises when these factors are present to different degrees among the exposed and unexposed study participants, but not all differences between the groups result in confounding. Thinking about an ideal study where all of the population of interest is exposed in one universe and is unexposed in a parallel universe helps to distinguish confounders from other differences. In an actual study, an observed unexposed population is chosen to stand in for the unobserved parallel universe. Differences between this substitute population and the parallel universe result in confounding. Confounding by identified factors can be addressed analytically and through study design, but only randomization has the potential to address confounding by unmeasured factors. Nevertheless, a given randomized study may still be confounded. Confounded study results can lead to incorrect conclusions about the effect of the exposure of interest on the outcome. © 2018 Nordic Federation of Societies of Obstetrics and Gynecology.

Analyzing partially missing confounder information in comparative effectiveness and safety research of therapeutics.

PubMed

Toh, Sengwee; García Rodríguez, Luis A; Hernán, Miguel A

2012-05-01

Electronic healthcare databases are commonly used in comparative effectiveness and safety research of therapeutics. Many databases now include additional confounder information in a subset of the study population through data linkage or data collection. We described and compared existing methods for analyzing such datasets. Using data from The Health Improvement Network and the relation between non-steroidal anti-inflammatory drugs and upper gastrointestinal bleeding as an example, we employed several methods to handle partially missing confounder information. The crude odds ratio (OR) of upper gastrointestinal bleeding was 1.50 (95% confidence interval: 0.98, 2.28) among selective cyclo-oxygenase-2 inhibitor initiators (n = 43 569) compared with traditional non-steroidal anti-inflammatory drug initiators (n = 411 616). The OR dropped to 0.81 (0.52, 1.27) upon adjustment for confounders recorded for all patients. When further considering three additional variables missing in 22% of the study population (smoking, alcohol consumption, body mass index), the OR was between 0.80 and 0.83 for the missing-category approach, the missing-indicator approach, single imputation by the most common category, multiple imputation by chained equations, and propensity score calibration. The OR was 0.65 (0.39, 1.09) and 0.67 (0.38, 1.16) for the unweighted and the inverse probability weighted complete-case analysis, respectively. Existing methods for handling partially missing confounder data require different assumptions and may produce different results. The unweighted complete-case analysis, the missing-category/indicator approach, and single imputation require often unrealistic assumptions and should be avoided. In this study, differences across methods were not substantial, likely due to relatively low proportion of missingness and weak confounding effect by the three additional variables upon adjustment for other variables. Copyright © 2012 John Wiley & Sons, Ltd.

Instrumental variable specifications and assumptions for longitudinal analysis of mental health cost offsets.

PubMed

O'Malley, A James

2012-12-01

Instrumental variables (IVs) enable causal estimates in observational studies to be obtained in the presence of unmeasured confounders. In practice, a diverse range of models and IV specifications can be brought to bear on a problem, particularly with longitudinal data where treatment effects can be estimated for various functions of current and past treatment. However, in practice the empirical consequences of different assumptions are seldom examined, despite the fact that IV analyses make strong assumptions that cannot be conclusively tested by the data. In this paper, we consider several longitudinal models and specifications of IVs. Methods are applied to data from a 7-year study of mental health costs of atypical and conventional antipsychotics whose purpose was to evaluate whether the newer and more expensive atypical antipsychotic medications lead to a reduction in overall mental health costs.

Sensitivity analysis for direct and indirect effects in the presence of exposure-induced mediator-outcome confounders

PubMed Central

Chiba, Yasutaka

2014-01-01

Questions of mediation are often of interest in reasoning about mechanisms, and methods have been developed to address these questions. However, these methods make strong assumptions about the absence of confounding. Even if exposure is randomized, there may be mediator-outcome confounding variables. Inference about direct and indirect effects is particularly challenging if these mediator-outcome confounders are affected by the exposure because in this case these effects are not identified irrespective of whether data is available on these exposure-induced mediator-outcome confounders. In this paper, we provide a sensitivity analysis technique for natural direct and indirect effects that is applicable even if there are mediator-outcome confounders affected by the exposure. We give techniques for both the difference and risk ratio scales and compare the technique to other possible approaches. PMID:25580387

Controlling for confounding variables in MS-omics protocol: why modularity matters.

PubMed

Smith, Rob; Ventura, Dan; Prince, John T

2014-09-01

As the field of bioinformatics research continues to grow, more and more novel techniques are proposed to meet new challenges and improvements upon solutions to long-standing problems. These include data processing techniques and wet lab protocol techniques. Although the literature is consistently thorough in experimental detail and variable-controlling rigor for wet lab protocol techniques, bioinformatics techniques tend to be less described and less controlled. As the validation or rejection of hypotheses rests on the experiment's ability to isolate and measure a variable of interest, we urge the importance of reducing confounding variables in bioinformatics techniques during mass spectrometry experimentation. © The Author 2013. Published by Oxford University Press. For Permissions, please email: journals.permissions@oup.com.

Assessing mediation using marginal structural models in the presence of confounding and moderation

PubMed Central

Coffman, Donna L.; Zhong, Wei

2012-01-01

This paper presents marginal structural models (MSMs) with inverse propensity weighting (IPW) for assessing mediation. Generally, individuals are not randomly assigned to levels of the mediator. Therefore, confounders of the mediator and outcome may exist that limit causal inferences, a goal of mediation analysis. Either regression adjustment or IPW can be used to take confounding into account, but IPW has several advantages. Regression adjustment of even one confounder of the mediator and outcome that has been influenced by treatment results in biased estimates of the direct effect (i.e., the effect of treatment on the outcome that does not go through the mediator). One advantage of IPW is that it can properly adjust for this type of confounding, assuming there are no unmeasured confounders. Further, we illustrate that IPW estimation provides unbiased estimates of all effects when there is a baseline moderator variable that interacts with the treatment, when there is a baseline moderator variable that interacts with the mediator, and when the treatment interacts with the mediator. IPW estimation also provides unbiased estimates of all effects in the presence of non-randomized treatments. In addition, for testing mediation we propose a test of the null hypothesis of no mediation. Finally, we illustrate this approach with an empirical data set in which the mediator is continuous, as is often the case in psychological research. PMID:22905648

Assessing mediation using marginal structural models in the presence of confounding and moderation.

PubMed

Coffman, Donna L; Zhong, Wei

2012-12-01

This article presents marginal structural models with inverse propensity weighting (IPW) for assessing mediation. Generally, individuals are not randomly assigned to levels of the mediator. Therefore, confounders of the mediator and outcome may exist that limit causal inferences, a goal of mediation analysis. Either regression adjustment or IPW can be used to take confounding into account, but IPW has several advantages. Regression adjustment of even one confounder of the mediator and outcome that has been influenced by treatment results in biased estimates of the direct effect (i.e., the effect of treatment on the outcome that does not go through the mediator). One advantage of IPW is that it can properly adjust for this type of confounding, assuming there are no unmeasured confounders. Further, we illustrate that IPW estimation provides unbiased estimates of all effects when there is a baseline moderator variable that interacts with the treatment, when there is a baseline moderator variable that interacts with the mediator, and when the treatment interacts with the mediator. IPW estimation also provides unbiased estimates of all effects in the presence of nonrandomized treatments. In addition, for testing mediation we propose a test of the null hypothesis of no mediation. Finally, we illustrate this approach with an empirical data set in which the mediator is continuous, as is often the case in psychological research. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Directed acyclic graphs (DAGs): an aid to assess confounding in dental research.

PubMed

Merchant, Anwar T; Pitiphat, Waranuch

2002-12-01

Confounding, a special type of bias, occurs when an extraneous factor is associated with the exposure and independently affects the outcome. In order to get an unbiased estimate of the exposure-outcome relationship, we need to identify potential confounders, collect information on them, design appropriate studies, and adjust for confounding in data analysis. However, it is not always clear which variables to collect information on and adjust for in the analyses. Inappropriate adjustment for confounding can even introduce bias where none existed. Directed acyclic graphs (DAGs) provide a method to select potential confounders and minimize bias in the design and analysis of epidemiological studies. DAGs have been used extensively in expert systems and robotics. Robins (1987) introduced the application of DAGs in epidemiology to overcome shortcomings of traditional methods to control for confounding, especially as they related to unmeasured confounding. DAGs provide a quick and visual way to assess confounding without making parametric assumptions. We introduce DAGs, starting with definitions and rules for basic manipulation, stressing more on applications than theory. We then demonstrate their application in the control of confounding through examples of observational and cross-sectional epidemiological studies.

Dialyzer Reuse with Peracetic Acid Does Not Impact Patient Mortality

PubMed Central

Bond, T. Christopher; Krishnan, Mahesh; Wilson, Steven M.; Mayne, Tracy

2011-01-01

Summary Background and objectives Numerous studies have shown the overall benefits of dialysis filter reuse, including superior biocompatibility and decreased nonbiodegradable medical waste generation, without increased risk of mortality. A recent study reported that dialyzer reprocessing was associated with decreased patient survival; however, it did not control for sources of potential confounding. We sought to determine the effect of dialyzer reprocessing with peracetic acid on patient mortality using contemporary outcomes data and rigorous analytical techniques. Design, setting, participants, & measurements We conducted a series of analyses of hemodialysis patients examining the effects of reuse on mortality using three techniques to control for potential confounding: instrumental variables, propensity-score matching, and time-dependent survival analysis. Results In the instrumental variables analysis, patients at high reuse centers had 16.2 versus 15.9 deaths/100 patient-years in nonreuse centers. In the propensity-score matched analysis, patients with reuse had a lower death rate per 100 patient-years than those without reuse (15.2 versus 15.5). The risk ratios for the time-dependent survival analyses were 0.993 (per percent of sessions with reuse) and 0.995 (per unit of last reuse), respectively. Over the study period, 13.8 million dialyzers were saved, representing 10,000 metric tons of medical waste. Conclusions Despite the large sample size, powered to detect miniscule effects, neither the instrumental variables nor propensity-matched analyses were statistically significant. The time-dependent survival analysis showed a protective effect of reuse. These data are consistent with the preponderance of evidence showing reuse limits medical waste generation without negatively affecting clinical outcomes. PMID:21566107

Overcoming ecologic bias using the two-phase study design.

PubMed

Wakefield, Jon; Haneuse, Sebastien J-P A

2008-04-15

Ecologic (aggregate) data are widely available and widely utilized in epidemiologic studies. However, ecologic bias, which arises because aggregate data cannot characterize within-group variability in exposure and confounder variables, can only be removed by supplementing ecologic data with individual-level data. Here the authors describe the two-phase study design as a framework for achieving this objective. In phase 1, outcomes are stratified by any combination of area, confounders, and error-prone (or discretized) versions of exposures of interest. Phase 2 data, sampled within each phase 1 stratum, provide accurate measures of exposure and possibly of additional confounders. The phase 1 aggregate-level data provide a high level of statistical power and a cross-classification by which individuals may be efficiently sampled in phase 2. The phase 2 individual-level data then provide a control for ecologic bias by characterizing the within-area variability in exposures and confounders. In this paper, the authors illustrate the two-phase study design by estimating the association between infant mortality and birth weight in several regions of North Carolina for 2000-2004, controlling for gender and race. This example shows that the two-phase design removes ecologic bias and produces gains in efficiency over the use of case-control data alone. The authors discuss the advantages and disadvantages of the approach.

Gene × environment interaction studies have not properly controlled for potential confounders: the problem and the (simple) solution.

PubMed

Keller, Matthew C

2014-01-01

Candidate gene × environment (G × E) interaction research tests the hypothesis that the effects of some environmental variable (e.g., childhood maltreatment) on some outcome measure (e.g., depression) depend on a particular genetic polymorphism. Because this research is inherently nonexperimental, investigators have been rightly concerned that detected interactions could be driven by confounders (e.g., ethnicity, gender, age, socioeconomic status) rather than by the specified genetic or environmental variables per se. In an attempt to eliminate such alternative explanations for detected G × E interactions, investigators routinely enter the potential confounders as covariates in general linear models. However, this practice does not control for the effects these variables might have on the G × E interaction. Rather, to properly control for confounders, researchers need to enter the covariate × environment and the covariate × gene interaction terms in the same model that tests the G × E term. In this manuscript, I demonstrate this point analytically and show that the practice of improperly controlling for covariates is the norm in the G × E interaction literature to date. Thus, many alternative explanations for G × E findings that investigators had thought were eliminated have not been. © 2013 Society of Biological Psychiatry Published by Society of Biological Psychiatry All rights reserved.

Methodological concerns for meta-analyses of meditation: Comment on Sedlmeier et al. (2012).

PubMed

Orme-Johnson, David W; Dillbeck, Michael C

2014-03-01

We commend Sedlmeier et al. (2012) for their significant undertaking of meta-analysis of all meditation types on all psychological variables, but additional analyses may modify some of their conclusions. Whereas they suggest from visual inspection of funnel diagrams that there may be publication bias of underreporting low-effect studies on the Transcendental Meditation (TM) technique, quantitative tests do not indicate the presence of bias for any type of meditation. We additionally found that there was no significant difference in effect sizes between studies originating from researchers affiliated with a TM organization and studies from other universities. We found that comparison of different types of meditation on their global index was confounded because their global index aggregated different sets of variables for the different groups. That is, using composite indices that only aggregated variables for which each group had at least 3 studies confirmed the authors' conclusion that effect sizes for different research designs were not different, but found that effect sizes for the TM technique were significantly larger than effect sizes for mindfulness meditation or other meditations. We also located 35 studies on the TM technique that appear to meet the authors' inclusion criteria that were missed by their meta-analysis, and several others on important psychosocial behavioral variables, such as job performance, substance abuse, and prison recidivism that were not reviewed. In addition, we suggest that future meta-analyses on psychological variables include cross-validating physiological studies.

Sociodemographic, lifestyle, and psychosocial determinants of hair cortisol in a South London community sample.

PubMed

Fischer, Susanne; Duncko, Roman; Hatch, Stephani L; Papadopoulos, Andrew; Goodwin, Laura; Frissa, Souci; Hotopf, Matthew; Cleare, Anthony J

2017-02-01

Hypothalamic-pituitary-adrenal (HPA) measures are crucial for research into stress and stress-related disorders. Most HPA measures fluctuate depending on diurnal rhythms and state confounders. Hair cortisol concentrations (HCC) are less susceptible to such fluctuations, but less is known about trait-like confounders. Using a community sample, we tested the relationship between HCC and a range of variables including demographic variables, hair treatment, and medication, as well as psychosocial variables, namely childhood trauma, critical life events, and depressive symptoms. Hair samples were collected from 144 individuals from the South East London Community Health (SELCoH) study. Childhood trauma, life events, and depressive symptoms were measured, together with age, sex, ethnicity, relationship status, educational attainment, employment status, occupational social class, hair washing frequency, hair treatments, season reflected in the hair sample, hazardous drinking, smoking, medication intake, and body mass index. Hair samples reflecting the past 3 months were collected and analysed using immunoassays. First, correlations (continuous variables) and simple linear regressions (dichotomous variables) were conducted to identify sociodemographic, hair-related, and lifestyle determinants of HCC. Next, multiple linear regressions were conducted to test the relationship between psychosocial variables and HCC when controlling for the identified confounders. Age (r=-0.17, p=0.050), White British ethnicity (β=-0.19, p=0.023), heat-based treatments (β=-0.22, p=0.010), and winter season (β=-0.18, p=0.024) were associated with lower HCC, whereas summer season (β=0.24, p=0.024), painkillers (β=0.25, p=0.003), anxiolytics/antidepressants (β=0.21, p=0.014), and hormonal contraceptives (β=0.27, p=0.006) were associated with higher HCC. Controlling for these confounders, physical neglect during childhood (β=-0.17, p=0.057), war-related experiences (β=0.20, p=0.027), separation (β=0.18, p=0.054), and being the victim of a serious crime (β=-0.17, p=0.062) were linked with altered HCC. Our findings suggest that variation in HCC occurs according to sociodemographic, hair-related, and lifestyle variables, and that certain associations between stress and altered HCC can only be revealed when accounting for these confounders. Copyright © 2016 Elsevier Ltd. All rights reserved.

Assessing treatment effects in older breast cancer patients: systematic review of observational research methods.

PubMed

de Glas, N A; Kiderlen, M; de Craen, A J M; Hamaker, M E; Portielje, J E A; van de Velde, C J H; Liefers, G J; Bastiaannet, E

2015-03-01

Solid evidence of treatment effects in older women with breast cancer is lacking, as they are generally underrepresented in randomized clinical trials on which guideline recommendations are based. An alternative way to study treatment effects in older patients could be to use data from observational studies. However, using appropriate methods in analyzing observational data is a key condition in order to draw valid conclusions, as directly comparing treatments generally results in biased estimates due to confounding by indication. The aim of this systematic review was to investigate the methods that have been used in observational studies that assessed the effects of breast cancer treatment on survival, breast cancer survival and recurrence in older patients (aged 65 years and older). Studies were identified through systematic review of the literature published between January 1st 2009 and December 13th 2013 in the PubMed database and EMBASe. Finally, 31 studies fulfilled the inclusion criteria. Of these, 22 studies directly compared two treatments. Fifteen out of these 22 studies addressed the problem of confounding by indication, while seven studies did not. Nine studies used some form of instrumental variable analysis. In conclusion, the vast majority of observational studies that investigate treatment effects in older breast cancer patients compared treatments directly. These studies are therefore likely to be biased. Observational research will be essential to improve treatment and outcome of older breast cancer patients, but the use of accurate methods is essential to draw valid conclusions from this type of data. Copyright © 2015 Elsevier Ltd. All rights reserved.

Cross-reactivity and masqueraders in seafood reactions.

PubMed

Banks, Taylor A; Gada, Satyen M

2013-01-01

Confounding variables play a significant role in many adverse seafood reactions and a clear understanding of these factors is important in properly characterizing reactions associated with potential masqueraders and mimics. Although the medical literature is replete with reviews of seafood hypersensitivity and reports of cross-reactive and newly characterized allergens, there has not been a recent effort to provide an updated overview of the several processes that may lead clinicians to draw incorrect conclusions in evaluating reported reactions to seafood. Ranging from seafood intoxications to other nonallergic or complex seafood reactions, these events can easily be misconstrued as representing a seafood IgE-mediated allergy. Among these are the more familiar topics of cross-reactivity and scombroid intoxication, and those with a still evolving understanding such as ciguatera fish poisoning and Anisakis reactions. This article seeks to provide an accessible but comprehensive summary of the relevant information surrounding these confounders in assessing adverse reactions to seafood. Such knowledge may be instrumental in unraveling complex or otherwise unclear presentations and aid clinicians in accurately evaluating and managing patients with reported seafood reactions.

Solar radiation increases suicide rate after adjusting for other climate factors in South Korea.

PubMed

Jee, Hee-Jung; Cho, Chul-Hyun; Lee, Yu Jin; Choi, Nari; An, Hyonggin; Lee, Heon-Jeong

2017-03-01

Previous studies have indicated that suicide rates have significant seasonal variations. There is seasonal discordance between temperature and solar radiation due to the monsoon season in South Korea. We investigated the seasonality of suicide and assessed its association with climate variables in South Korea. Suicide rates were obtained from the National Statistical Office of South Korea, and climatic data were obtained from the Korea Meteorological Administration for the period of 1992-2010. We conducted analyses using a generalized additive model (GAM). First, we explored the seasonality of suicide and climate variables such as mean temperature, daily temperature range, solar radiation, and relative humidity. Next, we identified confounding climate variables associated with suicide rate. To estimate the adjusted effect of solar radiation on the suicide rate, we investigated the confounding variables using a multivariable GAM. Suicide rate showed seasonality with a pattern similar to that of solar radiation. We found that the suicide rate increased 1.008 times when solar radiation increased by 1 MJ/m 2 after adjusting for other confounding climate factors (P < 0.001). Solar radiation has a significant linear relationship with suicide after adjusting for region, other climate variables, and time trends. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

How Confounder Strength Can Affect Allocation of Resources in Electronic Health Records.

PubMed

Lynch, Kristine E; Whitcomb, Brian W; DuVall, Scott L

2018-01-01

When electronic health record (EHR) data are used, multiple approaches may be available for measuring the same variable, introducing potentially confounding factors. While additional information may be gleaned and residual confounding reduced through resource-intensive assessment methods such as natural language processing (NLP), whether the added benefits offset the added cost of the additional resources is not straightforward. We evaluated the implications of misclassification of a confounder when using EHRs. Using a combination of simulations and real data surrounding hospital readmission, we considered smoking as a potential confounder. We compared ICD-9 diagnostic code assignment, which is an easily available measure but has the possibility of substantial misclassification of smoking status, with NLP, a method of determining smoking status that more expensive and time-consuming than ICD-9 code assignment but has less potential for misclassification. Classification of smoking status with NLP consistently produced less residual confounding than the use of ICD-9 codes; however, when minimal confounding was present, differences between the approaches were small. When considerable confounding is present, investing in a superior measurement tool becomes advantageous.

Cannabis Use, Polysubstance Use, and Psychosis Spectrum Symptoms in a Community-Based Sample of US Youth

PubMed Central

Jones, Jason D.; Calkins, Monica E.; Scott, J. Cobb; Bach, Emily C.; Gur, Raquel E.

2017-01-01

Purpose To examine how cannabis use and polysubstance use among cannabis users relate to psychosis spectrum (PS) symptoms in a large community-based sample of US youth. Methods 4,171 youth (age 14–21; mean=16.90, SD=1.85; 55% female) from the Philadelphia Neurodevelopmental Cohort (PNC) completed assessments of substance use, PS symptoms, and confounding variables (e.g., demographics, comorbid psychopathology, trauma exposure). Results After adjusting for confounds, cannabis use by itself was not associated with increased odds of being classified as “psychosis spectrum.” However, cannabis use in combination with tobacco or other substance use was associated with increased odds of PS classification (adjusted odds ratios [ORs] = 1.37 to 1.76). Follow-up symptom-level analyses revealed that cannabis use in combination with other substances was associated with subclinical positive symptoms (ORs=1.95 and 2.24) and frequent cannabis use was associated with subclinical negative/disorganized symptoms (OR=2.14). However, these symptom-level findings were reduced to trends after correction for multiple comparisons. Neither cannabis use nor polysubstance use was associated with threshold delusions or hallucinations. Conclusions After adjusting for important confounds, there was minimal evidence for associations between cannabis use by itself and PS symptoms. More compelling evidence emerged for associations between polysubstance use among cannabis users and PS symptoms. This study highlights the importance of considering polysubstance use and confounds when examining associations between cannabis use and PS symptoms. Further longitudinal research is necessary to determine whether these findings represent causal associations or shared genetic and/or environmental vulnerability for substance use and PS symptoms. PMID:28318911

Mismeasurement and the resonance of strong confounders: correlated errors.

PubMed

Marshall, J R; Hastrup, J L; Ross, J S

1999-07-01

Confounding in epidemiology, and the limits of standard methods of control for an imperfectly measured confounder, have been understood for some time. However, most treatments of this problem are based on the assumption that errors of measurement in confounding and confounded variables are independent. This paper considers the situation in which a strong risk factor (confounder) and an inconsequential but suspected risk factor (confounded) are each measured with errors that are correlated; the situation appears especially likely to occur in the field of nutritional epidemiology. Error correlation appears to add little to measurement error as a source of bias in estimating the impact of a strong risk factor: it can add to, diminish, or reverse the bias induced by measurement error in estimating the impact of the inconsequential risk factor. Correlation of measurement errors can add to the difficulty involved in evaluating structures in which confounding and measurement error are present. In its presence, observed correlations among risk factors can be greater than, less than, or even opposite to the true correlations. Interpretation of multivariate epidemiologic structures in which confounding is likely requires evaluation of measurement error structures, including correlations among measurement errors.

Cancer biomarker discovery is improved by accounting for variability in general levels of drug sensitivity in pre-clinical models.

PubMed

Geeleher, Paul; Cox, Nancy J; Huang, R Stephanie

2016-09-21

We show that variability in general levels of drug sensitivity in pre-clinical cancer models confounds biomarker discovery. However, using a very large panel of cell lines, each treated with many drugs, we could estimate a general level of sensitivity to all drugs in each cell line. By conditioning on this variable, biomarkers were identified that were more likely to be effective in clinical trials than those identified using a conventional uncorrected approach. We find that differences in general levels of drug sensitivity are driven by biologically relevant processes. We developed a gene expression based method that can be used to correct for this confounder in future studies.

Use of instrumental variables in the analysis of generalized linear models in the presence of unmeasured confounding with applications to epidemiological research.

PubMed

Johnston, K M; Gustafson, P; Levy, A R; Grootendorst, P

2008-04-30

A major, often unstated, concern of researchers carrying out epidemiological studies of medical therapy is the potential impact on validity if estimates of treatment are biased due to unmeasured confounders. One technique for obtaining consistent estimates of treatment effects in the presence of unmeasured confounders is instrumental variables analysis (IVA). This technique has been well developed in the econometrics literature and is being increasingly used in epidemiological studies. However, the approach to IVA that is most commonly used in such studies is based on linear models, while many epidemiological applications make use of non-linear models, specifically generalized linear models (GLMs) such as logistic or Poisson regression. Here we present a simple method for applying IVA within the class of GLMs using the generalized method of moments approach. We explore some of the theoretical properties of the method and illustrate its use within both a simulation example and an epidemiological study where unmeasured confounding is suspected to be present. We estimate the effects of beta-blocker therapy on one-year all-cause mortality after an incident hospitalization for heart failure, in the absence of data describing disease severity, which is believed to be a confounder. 2008 John Wiley & Sons, Ltd

A guide for measurement of circulating metabolic hormones in rodents: Pitfalls during the pre-analytical phase

PubMed Central

Bielohuby, Maximilian; Popp, Sarah; Bidlingmaier, Martin

2012-01-01

Researchers analyse hormones to draw conclusions from changes in hormone concentrations observed under specific physiological conditions and to elucidate mechanisms underlying their biological variability. It is, however, frequently overlooked that also circumstances occurring after collection of biological samples can significantly affect the hormone concentrations measured, owing to analytical and pre-analytical variability. Whereas the awareness for such potential confounders is increasing in human laboratory medicine, there is sometimes limited consensus about the control of these factors in rodent studies. In this guide, we demonstrate how such factors can affect reliability and consequent interpretation of the data from immunoassay measurements of circulating metabolic hormones in rodent studies. We also compare the knowledge about such factors in rodent studies to recent recommendations established for biomarker studies in humans and give specific practical recommendations for the control of pre-analytical conditions in metabolic studies in rodents. PMID:24024118

Temperature Variability during Delirium in ICU Patients: An Observational Study

PubMed Central

van der Kooi, Arendina W.; Kappen, Teus H.; Raijmakers, Rosa J.; Zaal, Irene J.; Slooter, Arjen J. C.

2013-01-01

Introduction Delirium is an acute disturbance of consciousness and cognition. It is a common disorder in the intensive care unit (ICU) and associated with impaired long-term outcome. Despite its frequency and impact, delirium is poorly recognized by ICU-physicians and –nurses using delirium screening tools. A completely new approach to detect delirium is to use monitoring of physiological alterations. Temperature variability, a measure for temperature regulation, could be an interesting component to monitor delirium, but whether temperature regulation is different during ICU delirium has not yet been investigated. The aim of this study was to investigate whether ICU delirium is related to temperature variability. Furthermore, we investigated whether ICU delirium is related to absolute body temperature. Methods We included patients who experienced both delirium and delirium free days during ICU stay, based on the Confusion Assessment method for the ICU conducted by a research- physician or –nurse, in combination with inspection of medical records. We excluded patients with conditions affecting thermal regulation or therapies affecting body temperature. Daily temperature variability was determined by computing the mean absolute second derivative of the temperature signal. Temperature variability (primary outcome) and absolute body temperature (secondary outcome) were compared between delirium- and non-delirium days with a linear mixed model and adjusted for daily mean Richmond Agitation and Sedation Scale scores and daily maximum Sequential Organ Failure Assessment scores. Results Temperature variability was increased during delirium-days compared to days without delirium (βunadjusted=0.007, 95% confidence interval (CI)=0.004 to 0.011, p<0.001). Adjustment for confounders did not alter this result (βadjusted=0.005, 95% CI=0.002 to 0.008, p<0.001). Delirium was not associated with absolute body temperature (βunadjusted=-0.03, 95% CI=-0.17 to 0.10, p=0.61). This did not change after adjusting for confounders (βadjusted=-0.03, 95% CI=-0.17 to 0.10, p=0.63). Conclusions Our study suggests that temperature variability is increased during ICU delirium. PMID:24194955

Breast milk and cognitive development—the role of confounders: a systematic review

PubMed Central

Walfisch, Asnat; Sermer, Corey; Cressman, Alex; Koren, Gideon

2013-01-01

Objectives The association between breastfeeding and child cognitive development is conflicted by studies reporting positive and null effects. This relationship may be confounded by factors associated with breastfeeding, specifically maternal socioeconomic class and IQ. Design Systematic review of the literature. Setting and participants Any prospective or retrospective study, in any language, evaluating the association between breastfeeding and cognitive development using a validated method in healthy term infants, children or adults, was included. Primary and secondary outcome measures Extracted data included the study design, target population and sample size, breastfeeding exposure, cognitive development assessment tool used and participants’ age, summary of the results prior to, and following, adjustment for confounders, and all confounders adjusted for. Study quality was assessed as well. Results 84 studies met our inclusion criteria (34 rated as high quality, 26 moderate and 24 low quality). Critical assessment of accepted studies revealed the following associations: 21 null, 28 positive, 18 null after adjusting for confounders and 17 positive—diminished after adjusting for confounders. Directionality of effect did not correlate with study quality; however, studies showing a decreased effect after multivariate analysis were of superior quality compared with other study groupings (14/17 high quality, 82%). Further, studies that showed null or diminished effect after multivariate analysis corrected for significantly more confounders (7.7±3.4) as compared with those that found no change following adjustment (5.6±4.5, p=0.04). The majority of included studies were carried out during childhood (75%) and set in high-income countries (85.5%). Conclusions Much of the reported effect of breastfeeding on child neurodevelopment is due to confounding. It is unlikely that additional work will change the current synthesis. Future studies should attempt to rigorously control for all important confounders. Alternatively, study designs using sibling cohorts discordant for breastfeeding may yield more robust conclusions. PMID:23975102

A Comprehensive Analysis of the SRS-Schwab Adult Spinal Deformity Classification and Confounding Variables: A Prospective, Non-US Cross-sectional Study in 292 Patients.

PubMed

Hallager, Dennis Winge; Hansen, Lars Valentin; Dragsted, Casper Rokkjær; Peytz, Nina; Gehrchen, Martin; Dahl, Benny

2016-05-01

Cross-sectional analyses on a consecutive, prospective cohort. To evaluate the ability of the Scoliosis Research Society (SRS)-Schwab Adult Spinal Deformity Classification to group patients by widely used health-related quality-of-life (HRQOL) scores and examine possible confounding variables. The SRS-Schwab Adult Spinal Deformity Classification includes sagittal modifiers considered important for HRQOL and the clinical impact of the classification has been validated in patients from the International Spine Study Group database; however, equivocal results were reported for the Pelvic Tilt modifier and potential confounding variables were not evaluated. Between March 2013 and May 2014, all adult spinal deformity patients from our outpatient clinic with sufficient radiographs were prospectively enrolled. Analyses of HRQOL variance and post hoc analyses were performed for each SRS-Schwab modifier. Age, history of spine surgery, and aetiology of spinal deformity were considered potential confounders and their influence on the association between SRS-Schwab modifiers and aggregated Oswestry Disability Index (ODI) scores was evaluated with multivariate proportional odds regressions. P values were adjusted for multiple testing. Two hundred ninety-two of 460 eligible patients were included for analyses. The SRS-Schwab Classification significantly discriminated HRQOL scores between normal and abnormal sagittal modifier classifications. Individual grade comparisons showed equivocal results; however, Pelvic Tilt grade + versus +  + did not discriminate patients according to any HRQOL score. All modifiers showed significant proportional odds for worse aggregated ODI scores with increasing grade levels and the effects were robust to confounding. However, age group and aetiology had individual significant effects. The SRS-Schwab sagittal modifiers reliably grouped patients graded 0 versus + / +  + according to the most widely used HRQOL scores and the effects of increasing grade level on odds for worse ODI scores remained significant after adjusting for potential confounders. However, effects of age group and aetiology should not be neglected. 3.

An overview of confounding. Part 2: how to identify it and special situations.

PubMed

Howards, Penelope P

2018-04-01

Confounding biases study results when the effect of the exposure on the outcome mixes with the effects of other risk and protective factors for the outcome that are present differentially by exposure status. However, not all differences between the exposed and unexposed group cause confounding. Thus, sources of confounding must be identified before they can be addressed. Confounding is absent in an ideal study where all of the population of interest is exposed in one universe and is unexposed in a parallel universe. In an actual study, an observed unexposed population represents the unobserved parallel universe. Thinking about differences between this substitute population and the unexposed parallel universe helps identify sources of confounding. These differences can then be represented in a diagram that shows how risk and protective factors for the outcome are related to the exposure. Sources of confounding identified in the diagram should be addressed analytically and through study design. However, treating all factors that differ by exposure status as confounders without considering the structure of their relation to the exposure can introduce bias. For example, conditions affected by the exposure are not confounders. There are also special types of confounding, such as time-varying confounding and unfixable confounding. It is important to evaluate carefully whether factors of interest contribute to confounding because bias can be introduced both by ignoring potential confounders and by adjusting for factors that are not confounders. The resulting bias can result in misleading conclusions about the effect of the exposure of interest on the outcome. © 2018 Nordic Federation of Societies of Obstetrics and Gynecology.

Attendance at cultural events, reading books or periodicals, and making music or singing in a choir as determinants for survival: Swedish interview survey of living conditions.

PubMed Central

Bygren, L. O.; Konlaan, B. B.; Johansson, S. E.

1996-01-01

OBJECTIVES: To investigate the possible influence of attendance at cultural events, reading books or periodicals, making music or singing in a choir as determinants for survival. DESIGN: A simple random sample was drawn of 15,198 individuals aged 16-74 years. Of these, 85% (12,982) were interviewed by trained non-medical interviewers between 1982 and 1983 about cultural activities. They were followed up with respect to survival until 31 December 1991. SETTING: Swedish interview survey of living conditions comprising a random sample of the adult Swedish population. SUBJECTS: 12,675 people interviewed between 1982 and 1983. MAIN OUTCOME MEASURES: Survival of subjects after controlling for eight confounding variables: age, sex, education level, income, long term disease, social network, smoking, and physical exercise. RESULTS: 6,301 men and 6,374 women were followed up; 533 men and 314 women died during this period. The control variables influenced survival in the expected directions except for social network for men; a significant negative effective was found when the analysis was made separately for men and women. We found an influence on mortality when the eight control variables were controlled for in people who rarely attended events compared with those attending most often, the relative risk being 1.57 (95% confidence interval 1.18 to 2.09). CONCLUSION: Attendance at cultural events may have a positive influence on survival. Long term follow up of large samples with confounders that are well controlled for and with the cultural stimulation more highly specified should be used to try to falsify the hypothesis before experiments start. PMID:8990990

Are attractive men's faces masculine or feminine? The importance of controlling confounds in face stimuli.

PubMed

DeBruine, Lisa M; Jones, Benedict C; Smith, Finlay G; Little, Anthony C

2010-06-01

Women's preferences for male masculinity are highly variable. Although many researchers explain this variability as reflecting systematic individual differences in how women resolve the tradeoff between the costs and benefits of choosing a masculine partner, others suggest that methodological differences between studies are responsible. A recent study found general femininity preferences for judgments of faces that were manipulated in sexual dimorphism of shape but general masculinity preferences for judgments of faces that were based on perceived masculinity. Using the original stimuli, we replicated these previous results but found equivalent general femininity preferences for both types of faces when nonface confounds in the stimuli (e.g. hairstyle) were eliminated through masking. We conclude that care must be taken to control potential confounds in stimuli and that the influence of nonface cues on preferences for facial masculinity deserves further study.

Eliminating Survivor Bias in Two-stage Instrumental Variable Estimators.

PubMed

Vansteelandt, Stijn; Walter, Stefan; Tchetgen Tchetgen, Eric

2018-07-01

Mendelian randomization studies commonly focus on elderly populations. This makes the instrumental variables analysis of such studies sensitive to survivor bias, a type of selection bias. A particular concern is that the instrumental variable conditions, even when valid for the source population, may be violated for the selective population of individuals who survive the onset of the study. This is potentially very damaging because Mendelian randomization studies are known to be sensitive to bias due to even minor violations of the instrumental variable conditions. Interestingly, the instrumental variable conditions continue to hold within certain risk sets of individuals who are still alive at a given age when the instrument and unmeasured confounders exert additive effects on the exposure, and moreover, the exposure and unmeasured confounders exert additive effects on the hazard of death. In this article, we will exploit this property to derive a two-stage instrumental variable estimator for the effect of exposure on mortality, which is insulated against the above described selection bias under these additivity assumptions.

[The intelligence quotient and malnutrition. Iron deficiency and the lead concentration as confusing variables].

PubMed

Vega-Franco, L; Mejía, A M; Robles, B; Moreno, L; Pérez, Y

1991-11-01

This study gave us the opportunity to know the roles iron deficiency and the presence of lead in blood play, as confounding variables, in relation to the state of malnutrition and the intellect of those children. A sample of 169 school children were classified according to their state of nutrition, their condition in reference to serum iron and lead concentrations. In addition, their intelligence was evaluated. The results confirmed that those children with lower weights and heights registered lesser points of intelligence; in fact, iron deficiency cancels out the difference in favor of those taller and weighing more. Lead did not contribute as a confounding variable, but more than half of the children showed possible toxic levels of this metal.

Symptom Severity Predicts Prolonged Recovery after Sport-Related Concussion: Age and Amnesia Do Not

PubMed Central

Meehan, William P.; Mannix, Rebekah C.; Stracciolini, Andrea; Elbin, R.J.; Collins, Michael W.

2013-01-01

Objective To identify predictors of prolonged symptoms for athletes who sustain concussions. Study design We conducted a multi-center, prospective, cohort study of patients in 2 sport concussion clinics. Possible predictors of prolonged symptoms from concussion were compared between two groups: those whose symptoms resolved within 28 days and those whose symptoms persisted beyond 28 days. Candidate predictor variables were entered into a logistic regression model that was used to generate adjusted odds ratios. Results During the study period, 182 patients met inclusion criteria. The mean age was 15.2 years (SD 3.04 years). Over a third (N=65) of patients underwent computerized neurocognitive testing on their initial visit. In univariate analyses, Post Concussion Symptom Scale (PCSS) score and all composite scores on computerized neurocognitive testing appeared to be associated with prolonged symptom duration. Sex, age, loss of consciousness at time of injury and amnesia at time of injury were not associated with prolonged symptom duration. After adjusting for potential confounding, however, only total score on the PCSS score was associated with the odds of suffering prolonged symptoms. Conclusions After adjusting for other potential confounding variables, only total score on the PCSS was associated with the odds of suffering prolonged symptoms from sport-related concussions; age and amnesia were not. Further efforts to develop clinical tools for predicting which athletes will suffer prolonged recoveries after concussion should focus on initial symptom score. PMID:23628374

Confounding by dietary patterns of the inverse association between alcohol consumption and type 2 diabetes risk.

PubMed

Imamura, Fumiaki; Lichtenstein, Alice H; Dallal, Gerard E; Meigs, James B; Jacques, Paul F

2009-07-01

The ability to interpret epidemiologic observations is limited because of potential residual confounding by correlated dietary components. Dietary pattern analyses by factor analysis or partial least squares may overcome the limitation. To examine confounding by dietary pattern as well as standard risk factors and selected nutrients, the authors modeled the longitudinal association between alcohol consumption and 7-year risk of type 2 diabetes mellitus in 2,879 healthy adults enrolled in the Framingham Offspring Study (1991-2001) by Cox proportional hazard models. After adjustment for standard risk factors, consumers of > or =9.0 drinks/week had a significantly lower risk of type 2 diabetes mellitus compared with abstainers (hazard ratio = 0.47, 95% confidence interval (CI): 0.27, 0.81). Adjustment for selected nutrients had little effect on the hazard ratio, whereas adjustment for dietary pattern variables by factor analysis significantly shifted the hazard ratio away from null (hazard ratio = 0.33, 95% CI: 0.17, 0.64) by 40.0% (95% CI: 16.8, 57.0; P = 0.002). Dietary pattern variables by partial least squares showed similar results. Therefore, the observed inverse association, consistent with past studies, was confounded by dietary patterns, and this confounding was not captured by individual nutrient adjustment. The data suggest that alcohol intake, not dietary patterns associated with alcohol intake, is responsible for the observed inverse association with type 2 diabetes mellitus risk.

The impact of confounder selection in propensity scores when applied to prospective cohort studies in pregnancy.

PubMed

Xu, Ronghui; Hou, Jue; Chambers, Christina D

2018-06-01

Our work was motivated by small cohort studies on the risk of birth defects in infants born to pregnant women exposed to medications. We controlled for confounding using propensity scores (PS). The extremely rare events setting renders the matching or stratification infeasible. In addition, the PS itself may be formed via different approaches to select confounders from a relatively long list of potential confounders. We carried out simulation experiments to compare different combinations of approaches: IPW or regression adjustment, with 1) including all potential confounders without selection, 2) selection based on univariate association between the candidate variable and the outcome, 3) selection based on change in effects (CIE). The simulation showed that IPW without selection leads to extremely large variances in the estimated odds ratio, which help to explain the empirical data analysis results that we had observed. Copyright © 2018 Elsevier Inc. All rights reserved.

Regular Tooth Brushing is Associated with a Decreased Risk of Metabolic Syndrome According to a Medical Check-Up Database.

PubMed

Tsutsumi, Chiyo; Kakuma, Tatsuyuki

2015-01-01

Associations have been reported between periodontal disease and increased cardiovascular disease risk, as well as between healthy self-reported tooth brushing behavior and reduced cardiovascular disease risk. We examined the association between self-reported tooth brushing behavior and the risk of metabolic syndrome (MetS) using a large medical check-up database. A total of 12,548 medical checkup records from a medical screening center in a city in southwest Japan were assessed. Subjects were aged 30 to 59 years. As lifestyle is associated with both tooth brushing and MetS, many lifestyle variables were considered as potential confounders. Logistic regression model were employed with a list of 127 lifestyle variables. Twenty variables associated with both tooth brushing and MetS were selected for both males and females. Furthermore, final confounding variables were selected by principal component analysis to avoid collinearity problems. The association of tooth brushing and MetS was evaluated for males and females separately by calculating adjusted odds ratios (ORs) with selected confounders plus age. The association between daily tooth brushing frequency and MetS risk for both genders was significant after adjusting for confounders, with the risk of MetS decreasing with increased frequency of daily tooth brushing (adjusted OR = 0.57 (95%Cl:0.48-0.81), 0.50 (95%Cl:0.35-0.71), 0.42 (95%Cl: 0.29-0.61) for males and adjusted OR = 0.65 (95%Cl:0.48-0.87), 0.44 (95%Cl:0.32-0.62) for females). Therefore, oral hygiene, including the frequency of tooth brushing as a significant component, may be an important factor in preventing MetS.

The Combined Effects of Measurement Error and Omitting Confounders in the Single-Mediator Model

PubMed Central

Fritz, Matthew S.; Kenny, David A.; MacKinnon, David P.

2016-01-01

Mediation analysis requires a number of strong assumptions be met in order to make valid causal inferences. Failing to account for violations of these assumptions, such as not modeling measurement error or omitting a common cause of the effects in the model, can bias the parameter estimates of the mediated effect. When the independent variable is perfectly reliable, for example when participants are randomly assigned to levels of treatment, measurement error in the mediator tends to underestimate the mediated effect, while the omission of a confounding variable of the mediator to outcome relation tends to overestimate the mediated effect. Violations of these two assumptions often co-occur, however, in which case the mediated effect could be overestimated, underestimated, or even, in very rare circumstances, unbiased. In order to explore the combined effect of measurement error and omitted confounders in the same model, the impact of each violation on the single-mediator model is first examined individually. Then the combined effect of having measurement error and omitted confounders in the same model is discussed. Throughout, an empirical example is provided to illustrate the effect of violating these assumptions on the mediated effect. PMID:27739903

Spatial Variability of Geriatric Depression Risk in a High-Density City: A Data-Driven Socio-Environmental Vulnerability Mapping Approach.

PubMed

Ho, Hung Chak; Lau, Kevin Ka-Lun; Yu, Ruby; Wang, Dan; Woo, Jean; Kwok, Timothy Chi Yui; Ng, Edward

2017-08-31

Previous studies found a relationship between geriatric depression and social deprivation. However, most studies did not include environmental factors in the statistical models, introducing a bias to estimate geriatric depression risk because the urban environment was found to have significant associations with mental health. We developed a cross-sectional study with a binomial logistic regression to examine the geriatric depression risk of a high-density city based on five social vulnerability factors and four environmental measures. We constructed a socio-environmental vulnerability index by including the significant variables to map the geriatric depression risk in Hong Kong, a high-density city characterized by compact urban environment and high-rise buildings. Crude and adjusted odds ratios (ORs) of the variables were significantly different, indicating that both social and environmental variables should be included as confounding factors. For the comprehensive model controlled by all confounding factors, older adults who were of lower education had the highest geriatric depression risks (OR: 1.60 (1.21, 2.12)). Higher percentage of residential area and greater variation in building height within the neighborhood also contributed to geriatric depression risk in Hong Kong, while average building height had negative association with geriatric depression risk. In addition, the socio-environmental vulnerability index showed that higher scores were associated with higher geriatric depression risk at neighborhood scale. The results of mapping and cross-section model suggested that geriatric depression risk was associated with a compact living environment with low socio-economic conditions in historical urban areas in Hong Kong. In conclusion, our study found a significant difference in geriatric depression risk between unadjusted and adjusted models, suggesting the importance of including environmental factors in estimating geriatric depression risk. We also developed a framework to map geriatric depression risk across a city, which can be used for identifying neighborhoods with higher risk for public health surveillance and sustainable urban planning.

Association of Body Mass Index with Depression, Anxiety and Suicide—An Instrumental Variable Analysis of the HUNT Study

PubMed Central

Bjørngaard, Johan Håkon; Carslake, David; Lund Nilsen, Tom Ivar; Linthorst, Astrid C. E.; Davey Smith, George; Gunnell, David; Romundstad, Pål Richard

2015-01-01

Objective While high body mass index is associated with an increased risk of depression and anxiety, cumulative evidence indicates that it is a protective factor for suicide. The associations from conventional observational studies of body mass index with mental health outcomes are likely to be influenced by reverse causality or confounding by ill-health. In the present study, we investigated the associations between offspring body mass index and parental anxiety, depression and suicide in order to avoid problems with reverse causality and confounding by ill-health. Methods We used data from 32,457 mother-offspring and 27,753 father-offspring pairs from the Norwegian HUNT-study. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale and suicide death from national registers. Associations between offspring and own body mass index and symptoms of anxiety and depression and suicide mortality were estimated using logistic and Cox regression. Causal effect estimates were estimated with a two sample instrument variable approach using offspring body mass index as an instrument for parental body mass index. Results Both own and offspring body mass index were positively associated with depression, while the results did not indicate any substantial association between body mass index and anxiety. Although precision was low, suicide mortality was inversely associated with own body mass index and the results from the analysis using offspring body mass index supported these results. Adjusted odds ratios per standard deviation body mass index from the instrumental variable analysis were 1.22 (95% CI: 1.05, 1.43) for depression, 1.10 (95% CI: 0.95, 1.27) for anxiety, and the instrumental variable estimated hazard ratios for suicide was 0.69 (95% CI: 0.30, 1.63). Conclusion The present study’s results indicate that suicide mortality is inversely associated with body mass index. We also found support for a positive association between body mass index and depression, but not for anxiety. PMID:26167892

Spatial Variability of Geriatric Depression Risk in a High-Density City: A Data-Driven Socio-Environmental Vulnerability Mapping Approach

PubMed Central

Lau, Kevin Ka-Lun; Yu, Ruby; Wang, Dan; Kwok, Timothy Chi Yui; Ng, Edward

2017-01-01

Previous studies found a relationship between geriatric depression and social deprivation. However, most studies did not include environmental factors in the statistical models, introducing a bias to estimate geriatric depression risk because the urban environment was found to have significant associations with mental health. We developed a cross-sectional study with a binomial logistic regression to examine the geriatric depression risk of a high-density city based on five social vulnerability factors and four environmental measures. We constructed a socio-environmental vulnerability index by including the significant variables to map the geriatric depression risk in Hong Kong, a high-density city characterized by compact urban environment and high-rise buildings. Crude and adjusted odds ratios (ORs) of the variables were significantly different, indicating that both social and environmental variables should be included as confounding factors. For the comprehensive model controlled by all confounding factors, older adults who were of lower education had the highest geriatric depression risks (OR: 1.60 (1.21, 2.12)). Higher percentage of residential area and greater variation in building height within the neighborhood also contributed to geriatric depression risk in Hong Kong, while average building height had negative association with geriatric depression risk. In addition, the socio-environmental vulnerability index showed that higher scores were associated with higher geriatric depression risk at neighborhood scale. The results of mapping and cross-section model suggested that geriatric depression risk was associated with a compact living environment with low socio-economic conditions in historical urban areas in Hong Kong. In conclusion, our study found a significant difference in geriatric depression risk between unadjusted and adjusted models, suggesting the importance of including environmental factors in estimating geriatric depression risk. We also developed a framework to map geriatric depression risk across a city, which can be used for identifying neighborhoods with higher risk for public health surveillance and sustainable urban planning. PMID:28858265

Biasogram: Visualization of Confounding Technical Bias in Gene Expression Data

PubMed Central

Krzystanek, Marcin; Szallasi, Zoltan; Eklund, Aron C.

2013-01-01

Gene expression profiles of clinical cohorts can be used to identify genes that are correlated with a clinical variable of interest such as patient outcome or response to a particular drug. However, expression measurements are susceptible to technical bias caused by variation in extraneous factors such as RNA quality and array hybridization conditions. If such technical bias is correlated with the clinical variable of interest, the likelihood of identifying false positive genes is increased. Here we describe a method to visualize an expression matrix as a projection of all genes onto a plane defined by a clinical variable and a technical nuisance variable. The resulting plot indicates the extent to which each gene is correlated with the clinical variable or the technical variable. We demonstrate this method by applying it to three clinical trial microarray data sets, one of which identified genes that may have been driven by a confounding technical variable. This approach can be used as a quality control step to identify data sets that are likely to yield false positive results. PMID:23613961

Housing conditions and mental health in a disadvantaged area in Scotland.

PubMed Central

Hopton, J L; Hunt, S M

1996-01-01

OBJECTIVE: To examine the mental health impact of different aspects of poor housing. DESIGN: This was a post hoc analysis of data from a household interview survey. SETTING: A public sector housing estate on the outskirts of Glasgow. SUBJECTS: These comprised 114 men and 333 women aged between 17 and 65 from 451 households. MEASURES: Dependent variable: scoring > or = 5 on the 30 item general health questionnaire (GHQ30). Independent variables: self reported data on household composition, whether ill health was a factor in the move to the current dwelling, length of time at address, household income, whether the respondent was employed, chronic illness, and 6 problems with the dwelling. RESULTS: Reporting a problem with dampness was significantly and independently associated with scores of > or = 5 on the GHQ30 after controlling for possible confounding variables. CONCLUSION: Initiatives to tackle housing dampness may be important in developing a strategy to improve mental health for the study area. More research on the mental health impact of different aspects of poor housing is required. PMID:8762355

Delayed Ego Strength Development in Opioid Dependent Adolescents and Young Adults.

PubMed

Abramoff, Benjamin A; Lange, Hannah L H; Matson, Steven C; Cottrill, Casey B; Bridge, Jeffrey A; Abdel-Rasoul, Mahmoud; Bonny, Andrea E

2015-01-01

Objective. To evaluate ego strengths, in the context of Erikson's framework, among adolescents and young adults diagnosed with opioid dependence as compared to non-drug using youth. Methods. Opioid dependent (n = 51) and non-drug using control (n = 31) youth completed the self-administered Psychosocial Inventory of Ego Strengths (PIES). The PIES assesses development in the framework of Erikson's ego strength stages. Multivariate linear regression modeling assessed the independent association of the primary covariate (opioid dependent versus control) as well as potential confounding variables (e.g., psychiatric comorbidities, intelligence) with total PIES score. Results. Mean total PIES score was significantly lower in opioid dependent youth (231.65 ± 30.39 opioid dependent versus 270.67 ± 30.06 control; p < 0.01). Evaluation of the PIES subscores found significant (p < 0.05) delays in all ego strength areas (hope, will, purpose, competence, fidelity, love, care, and wisdom). When adjusting for potential confounders, opioid dependence remained a significant (p < 0.001) independent predictor of total PIES score. Conclusion. Adolescents with opioid dependence demonstrated significant delays in ego strength development. A treatment approach acknowledging this delay may be needed in the counseling and treatment of adolescents with opioid dependence.

Associations among Obesity, Eating Speed, and Oral Health

PubMed Central

Sonoda, Chikanobu; Fukuda, Hideki; Kitamura, Masayasu; Hayashida, Hideaki; Kawashita, Yumiko; Furugen, Reiko; Koyama, Zenya; Saito, Toshiyuki

2018-01-01

Objective This study was conducted to understand how eating speed and oral health condition are associated with obesity in Japanese working men. Methods We studied a total of 863 men attending an annual medical checkup of the Japanese Maritime Self Defense Force in Sasebo City, Japan. Participants answered a questionnaire about their eating speed, and we examined their anthropometric status in terms of BMI, waist circumference, and oral health condition, especially periodontal disease and number of functional teeth. Multivariate logistic regression analyses adjusting for potential confounding variables were performed. Results The multivariate-adjusted odds ratio for waist circumference greater than 90 cm of the ‘very fast’ group compared to the ‘slow, very slow’ group was 5.22 (95% confidence interval 1.81–15.06) after adjusting for potential confounding factors. Individuals were more likely to have waist circumference greater than 90 cm if they had a larger ‘number of missing functional teeth’ (odds ratio 1.14; 95% confidence interval 1.01–1.28) and severe periodontal disease (odds ratio 2.74; 95% confidence interval, 1.46–5.13). Conclusion Eating speed, the number of missing functional teeth, and severe periodontal disease are associated independently with larger waist circumference. PMID:29669358

The health consequences of maquiladora work: women on the US-Mexican border.

PubMed Central

Guendelman, S; Silberg, M J

1993-01-01

OBJECTIVES. As more US companies take jobs to Mexico, complaints are growing that the assembly plants (maquiladoras) exert adverse effects on workers' health. This study assessed the health of female electronic and garment maquiladora workers, comparing them with women employed in services and non-wage earners. METHODS. A survey was administered to 480 women living in Tijuana in 1990. The sample was stratified by occupation and length of employment. Functional impediments, nervousness, depression, and sense of control were used as outcome variables, controlling for other confounders. RESULTS. Despite working longer hours, receiving lower wages, and having less decision latitude and education, maquiladora workers were not worse off than service workers. Maquiladora workers reported similar incidences of depression and lack of control over life. Electronics workers, especially, had lower incidences of nervousness and functional impediments, after controlling for other confounders. Also, maquiladora work did not add an extra health burden compared with non-wage earners. CONCLUSIONS. The adverse effects of maquiladoras previously reported may have been exaggerated. Subjective factors, including negative attitudes toward economic adversity and work dissatisfaction, were stronger predictors of health than were objective indicators. PMID:8417604

Delayed Ego Strength Development in Opioid Dependent Adolescents and Young Adults

PubMed Central

Abramoff, Benjamin A.; Lange, Hannah L. H.; Matson, Steven C.; Cottrill, Casey B.; Bridge, Jeffrey A.; Abdel-Rasoul, Mahmoud; Bonny, Andrea E.

2015-01-01

Objective. To evaluate ego strengths, in the context of Erikson's framework, among adolescents and young adults diagnosed with opioid dependence as compared to non-drug using youth. Methods. Opioid dependent (n = 51) and non-drug using control (n = 31) youth completed the self-administered Psychosocial Inventory of Ego Strengths (PIES). The PIES assesses development in the framework of Erikson's ego strength stages. Multivariate linear regression modeling assessed the independent association of the primary covariate (opioid dependent versus control) as well as potential confounding variables (e.g., psychiatric comorbidities, intelligence) with total PIES score. Results. Mean total PIES score was significantly lower in opioid dependent youth (231.65 ± 30.39 opioid dependent versus 270.67 ± 30.06 control; p < 0.01). Evaluation of the PIES subscores found significant (p < 0.05) delays in all ego strength areas (hope, will, purpose, competence, fidelity, love, care, and wisdom). When adjusting for potential confounders, opioid dependence remained a significant (p < 0.001) independent predictor of total PIES score. Conclusion. Adolescents with opioid dependence demonstrated significant delays in ego strength development. A treatment approach acknowledging this delay may be needed in the counseling and treatment of adolescents with opioid dependence. PMID:26664819

On the definition of a confounder

PubMed Central

VanderWeele, Tyler J.; Shpitser, Ilya

2014-01-01

Summary The causal inference literature has provided a clear formal definition of confounding expressed in terms of counterfactual independence. The causal inference literature has not, however, produced a clear formal definition of a confounder, as it has given priority to the concept of confounding over that of a confounder. We consider a number of candidate definitions arising from various more informal statements made in the literature. We consider the properties satisfied by each candidate definition, principally focusing on (i) whether under the candidate definition control for all “confounders” suffices to control for “confounding” and (ii) whether each confounder in some context helps eliminate or reduce confounding bias. Several of the candidate definitions do not have these two properties. Only one candidate definition of those considered satisfies both properties. We propose that a “confounder” be defined as a pre-exposure covariate C for which there exists a set of other covariates X such that effect of the exposure on the outcome is unconfounded conditional on (X, C) but such that for no proper subset of (X, C) is the effect of the exposure on the outcome unconfounded given the subset. A variable that helps reduce bias but not eliminate bias we propose referring to as a “surrogate confounder.” PMID:25544784

Confounder Detection in High-Dimensional Linear Models Using First Moments of Spectral Measures.

PubMed

Liu, Furui; Chan, Laiwan

2018-06-12

In this letter, we study the confounder detection problem in the linear model, where the target variable [Formula: see text] is predicted using its [Formula: see text] potential causes [Formula: see text]. Based on an assumption of a rotation-invariant generating process of the model, recent study shows that the spectral measure induced by the regression coefficient vector with respect to the covariance matrix of [Formula: see text] is close to a uniform measure in purely causal cases, but it differs from a uniform measure characteristically in the presence of a scalar confounder. Analyzing spectral measure patterns could help to detect confounding. In this letter, we propose to use the first moment of the spectral measure for confounder detection. We calculate the first moment of the regression vector-induced spectral measure and compare it with the first moment of a uniform spectral measure, both defined with respect to the covariance matrix of [Formula: see text]. The two moments coincide in nonconfounding cases and differ from each other in the presence of confounding. This statistical causal-confounding asymmetry can be used for confounder detection. Without the need to analyze the spectral measure pattern, our method avoids the difficulty of metric choice and multiple parameter optimization. Experiments on synthetic and real data show the performance of this method.

Who really gets strep sore throat? Confounding and effect modification of a time-varying exposure on recurrent events.

PubMed

Follmann, Dean; Huang, Chiung-Yu; Gabriel, Erin

2016-10-30

Unmeasured confounding is the fundamental obstacle to drawing causal conclusions about the impact of an intervention from observational data. Typically, covariates are measured to eliminate or ameliorate confounding, but they may be insufficient or unavailable. In the special setting where a transient intervention or exposure varies over time within each individual and confounding is time constant, a different tack is possible. The key idea is to condition on either the overall outcome or the proportion of time in the intervention. These measures can eliminate the unmeasured confounding either by conditioning or by use of a proxy covariate. We evaluate existing methods and develop new models from which causal conclusions can be drawn from such observational data even if no baseline covariates are measured. Our motivation for this work was to determine the causal effect of Streptococcus bacteria in the throat on pharyngitis (sore throat) in Indian schoolchildren. Using our models, we show that existing methods can be badly biased and that sick children who are rarely colonized have a high probability that the Streptococcus bacteria are causing their disease. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Examining the Error of Mis-Specifying Nonlinear Confounding Effect With Application on Accelerometer-Measured Physical Activity.

PubMed

Lee, Paul H

2017-06-01

Some confounders are nonlinearly associated with dependent variables, but they are often adjusted using a linear term. The purpose of this study was to examine the error of mis-specifying the nonlinear confounding effect. We carried out a simulation study to investigate the effect of adjusting for a nonlinear confounder in the estimation of a causal relationship between the exposure and outcome in 3 ways: using a linear term, binning into 5 equal-size categories, or using a restricted cubic spline of the confounder. Continuous, binary, and survival outcomes were simulated. We examined the confounder across varying measurement error. In addition, we performed a real data analysis examining the 3 strategies to handle the nonlinear effects of accelerometer-measured physical activity in the National Health and Nutrition Examination Survey 2003-2006 data. The mis-specification of a nonlinear confounder had little impact on causal effect estimation for continuous outcomes. For binary and survival outcomes, this mis-specification introduced bias, which could be eliminated using spline adjustment only when there is small measurement error of the confounder. Real data analysis showed that the associations between high blood pressure, high cholesterol, and diabetes and mortality adjusted for physical activity with restricted cubic spline were about 3% to 11% larger than their counterparts adjusted with a linear term. For continuous outcomes, confounders with nonlinear effects can be adjusting with a linear term. Spline adjustment should be used for binary and survival outcomes on confounders with small measurement error.

Interpretational Confounding Is Due to Misspecification, Not to Type of Indicator: Comment on Howell, Breivik, and Wilcox (2007)

ERIC Educational Resources Information Center

Bollen, Kenneth A.

2007-01-01

R. D. Howell, E. Breivik, and J. B. Wilcox (2007) have argued that causal (formative) indicators are inherently subject to interpretational confounding. That is, they have argued that using causal (formative) indicators leads the empirical meaning of a latent variable to be other than that assigned to it by a researcher. Their critique of causal…

Causal diagrams and multivariate analysis III: confound it!

PubMed

Jupiter, Daniel C

2015-01-01

This commentary concludes my series concerning inclusion of variables in multivariate analyses. We take up the issues of confounding and effect modification and summarize the work we have thus far done. Finally, we provide a rough algorithm to help guide us through the maze of possibilities that we have outlined. Copyright © 2015 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Children's concepts of physical illness: a review and critique of the cognitive-developmental literature.

PubMed

Burbach, D J; Peterson, L

1986-01-01

Cognitive-developmental studies relevant to children's concepts of physical illness are reviewed and critiqued. Although numerous methodological weaknesses make firm conclusions difficult, most data appear to suggest that children's concepts of illness do evolve in a systematic and predictable sequence consistent with Piaget's theory of cognitive development. Methodological weaknesses identified include poor description of samples, assessment instruments, and procedures; lack of control over potential observer bias, expectancy effects, and other confounding variables; and minimal attention to reliability and validity issues. Increased methodological rigor and a further explication of the specific and unique ways in which children's concepts of illness develop over the course of cognitive development could substantially increase the value of these studies for professionals in pediatric health care settings.

Polychlorinated biphenyl exposure and effects in transformer repair workers.

PubMed Central

Emmett, E A

1985-01-01

Fifty-five present and past transformer repair workers exposed to polychlorinated biphenyls (PCBs) and 56 unexposed comparison workers were evaluated in a clinical-epidemiologic study. The groups were similar in most demographic variables. Adipose tissue lipid and serum PCBs concentrations were higher in current exposed workers (geometric means adipose 2.1 ppm, serum 12.2 ppb). Concentrations in comparison (0.6 ppm and 4.6 ppb) and previously exposed (0.83 ppm and 5.9 ppb) workers were lower. Statistically significant differences in serum albumin and lactic dehydrogenase, but not in other liver function tests, were seen between the exposed and comparison groups; however, after adjustment for confounding variables, no correlations were observed between liver function tests and either adipose or serum PCBs concentrations. Statistically significant correlation both before and after adjustment for confounding variables were seen with adipose PCBs and 24-hr urinary 17-hydroxycorticosteroid excretion and with serum PCBs and serum gamma-glutamyl transpeptidase. Both associations could reflect microsomal enzyme induction among other possibilities. No differences were seen in fasting serum triglycerides, total cholesterol, LDL, HDL or VLDL cholesterol between the two exposure groups. A statistically significant correlation between serum PCBs and serum triglycerides, total cholesterol, and VLDL cholesterol was removed by adjusting for confounding variables. No correlation was seen between adipose PCBs concentrations and any serum lipid component. Partition phenomena could account for these findings.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2863134

On causal interpretation of race in regressions adjusting for confounding and mediating variables

PubMed Central

VanderWeele, Tyler J.; Robinson, Whitney R.

2014-01-01

We consider several possible interpretations of the “effect of race” when regressions are run with race as an exposure variable, controlling also for various confounding and mediating variables. When adjustment is made for socioeconomic status early in a person’s life, we discuss under what contexts the regression coefficients for race can be interpreted as corresponding to the extent to which a racial inequality would remain if various socioeconomic distributions early in life across racial groups could be equalized. When adjustment is also made for adult socioeconomic status, we note how the overall racial inequality can be decomposed into the portion that would be eliminated by equalizing adult socioeconomic status across racial groups and the portion of the inequality that would remain even if adult socioeconomic status across racial groups were equalized. We also discuss a stronger interpretation of the “effect of race” (stronger in terms of assumptions) involving the joint effects of race-associated physical phenotype (e.g. skin color), parental physical phenotype, genetic background and cultural context when such variables are thought to be hypothetically manipulable and if adequate control for confounding were possible. We discuss some of the challenges with such an interpretation. Further discussion is given as to how the use of selected populations in examining racial disparities can additionally complicate the interpretation of the effects. PMID:24887159

The contribution of smoking to socioeconomic differentials in mortality: results from the Melbourne Collaborative Cohort Study, Australia

PubMed Central

Siahpush, Mohammad; English, Dallas; Powles, John

2006-01-01

Objective To assess the contribution of smoking to the inverse association of mortality with years of formal education in men in Australia. Design Data were obtained from a prospective cohort study that included 17 049 men in Melbourne recruited from 1990 to 1994, most of whom were aged between 40 and 69 years at baseline. The outcome measured was all‐cause mortality. The contribution of smoking to socioeconomic status differentials was estimated by including smoking as a variable in a Cox's proportional hazards model that also included education and other potential confounding variables. Results In men, the association between education and mortality was attenuated after adjustment for smoking, and the aetiological fraction for low levels of education was reduced from 16.5% to 10.6%. Conclusions In men, smoking contributes substantially to socioeconomic differentials in mortality. Effective policies and interventions that target smoking among socially disadvantaged groups may substantially reduce socioeconomic differentials in health. PMID:17108305

Divergent marijuana trajectories among men: Socioeconomic, relationship, and life satisfaction outcomes in the mid-30s

PubMed Central

White, Helene R.; Bechtold, Jordan; Loeber, Rolf; Pardini, Dustin

2016-01-01

Background Given recent changes in marijuana policy in the United States, it is important to understand the long-term effects of marijuana use on adult functioning. We examined whether men who displayed different trajectories of marijuana use from adolescence through emerging adulthood (age ~15–26) differed in terms of socioeconomic, social, and life satisfaction outcomes in their mid-30s. Methods Data came from a longitudinal sample of men who were recruited in early adolescence (N = 506) and followed into adulthood. Four trajectory groups based on patterns of marijuana use from adolescence into emerging adulthood were compared on adult outcomes (age ~36) before and after controlling for co-occurring use of other substances and several pre-existing confounding factors in early adolescence. The potential moderating effect of race was also examined. Results Although there were initially group differences across all domains, once pre-existing confounds and co-occurring other substance use were included in the model, groups only differed in terms of partner and friend marijuana use. Chronic marijuana users reported the highest proportions of both. Frequent and persistent marijuana use was associated with lower socioeconomic status (SES) for Black men only. Conclusions After statistically accounting for confounding variables, chronic marijuana users were not at a heightened risk for maladjustment in adulthood except for lower SES among Black men. Chronic users were more likely to have friends and partners who also used marijuana. Future studies should take into account pre-existing differences when examining outcomes of marijuana use. PMID:26365837

A New Method for Partial Correction of Residual Confounding in Time-Series and Other Observational Studies.

PubMed

Flanders, W Dana; Strickland, Matthew J; Klein, Mitchel

2017-05-15

Methods exist to detect residual confounding in epidemiologic studies. One requires a negative control exposure with 2 key properties: 1) conditional independence of the negative control and the outcome (given modeled variables) absent confounding and other model misspecification, and 2) associations of the negative control with uncontrolled confounders and the outcome. We present a new method to partially correct for residual confounding: When confounding is present and our assumptions hold, we argue that estimators from models that include a negative control exposure with these 2 properties tend to be less biased than those from models without it. Using regression theory, we provide theoretical arguments that support our claims. In simulations, we empirically evaluated the approach using a time-series study of ozone effects on asthma emergency department visits. In simulations, effect estimators from models that included the negative control exposure (ozone concentrations 1 day after the emergency department visit) had slightly or modestly less residual confounding than those from models without it. Theory and simulations show that including the negative control can reduce residual confounding, if our assumptions hold. Our method differs from available methods because it uses a regression approach involving an exposure-based indicator rather than a negative control outcome to partially correct for confounding. © The Author 2017. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Refining adverse drug reaction signals by incorporating interaction variables identified using emergent pattern mining.

PubMed

Reps, Jenna M; Aickelin, Uwe; Hubbard, Richard B

2016-02-01

To develop a framework for identifying and incorporating candidate confounding interaction terms into a regularised cox regression analysis to refine adverse drug reaction signals obtained via longitudinal observational data. We considered six drug families that are commonly associated with myocardial infarction in observational healthcare data, but where the causal relationship ground truth is known (adverse drug reaction or not). We applied emergent pattern mining to find itemsets of drugs and medical events that are associated with the development of myocardial infarction. These are the candidate confounding interaction terms. We then implemented a cohort study design using regularised cox regression that incorporated and accounted for the candidate confounding interaction terms. The methodology was able to account for signals generated due to confounding and a cox regression with elastic net regularisation correctly ranking the drug families known to be true adverse drug reactions above those that are not. This was not the case without the inclusion of the candidate confounding interaction terms, where confounding leads to a non-adverse drug reaction being ranked highest. The methodology is efficient, can identify high-order confounding interactions and does not require expert input to specify outcome specific confounders, so it can be applied for any outcome of interest to quickly refine its signals. The proposed method shows excellent potential to overcome some forms of confounding and therefore reduce the false positive rate for signal analysis using longitudinal data. Copyright © 2015 Elsevier Ltd. All rights reserved.

Association of Fatigue With Sarcopenia and its Elements: A Secondary Analysis of SABE-Bogotá

PubMed Central

Patino-Hernandez, Daniela; David-Pardo, David Gabriel; Borda, Miguel Germán; Pérez-Zepeda, Mario Ulises; Cano-Gutiérrez, Carlos

2017-01-01

Objective: Sarcopenia, fatigue, and depression are associated with higher mortality rates and adverse outcomes in the aging population. Understanding the association among clinical variables, mainly symptoms, is important for screening and appropriately managing these conditions. The aim of this article is to evaluate the association among sarcopenia and its elements with depression and fatigue. Method: We used cross-sectional data from 2012 SABE (Salud, Bienestar y Envejecimiento)-Bogotá study, which included 2,000 participants of ages ≥60 years. Sarcopenia and its elements were taken as the dependent variable, while fatigue and depression were the main independent variables. We tested the association among these through multiple logistic regression models, which were fitted for each dependent variable and adjusted for confounding variables. Results: Our findings showed that gait speed was associated with fatigue (adjusted odds ratio [OR] = 1.41, 95% confidence interval [CI] = [1.05, 1.90], p = .02) as well as abnormal handgrip strength (adjusted OR = 1.40, 95% CI = [1.02, 1.93], p = .04). No other associations were significant. Conclusion: While sarcopenia and fatigue are not associated, two of the sarcopenia-defining variables are associated with fatigue; this suggests that lack of sarcopenia does not exclude undesirable outcomes related to fatigue in aging adults. Also, the lack of association between sarcopenia-defining elements and depression demonstrates that depression and fatigue are different concepts. PMID:28474000

Inverse Association between Fruit and Vegetable Intake and BMI even after Controlling for Demographic, Socioeconomic and Lifestyle Factors

PubMed Central

Heo, Moonseong; Kim, Ryung S.; Wylie-Rosett, Judith; Allison, David B.; Heymsfield, Steve B.; Faith, Myles S.

2011-01-01

Objective To estimate fruit and vegetable (FV) intake levels of US adult population and evaluate the association between FV intake and BMI status after controlling for confounding demographic, socioeconomic and lifestyle factors. We also sought to identify moderating factors. Methods We used 2007 Behavior Risk Factors Surveillance System (N > 400,000) data. FV intake was dichotomized as ≥5 servings (FV5+) versus <5 servings/day. BMI status was categorized as normal, overweight, and obese. Identification of moderators was performed by testing interactions between BMI status and other variables using bivariate analyses followed by multiple logistic regression analysis incorporating complex survey sampling design features. Results Only 24.6% of US adults consumed ≥5 servings per day and less than 4% consumed 9 or more servings. Overweight (% FV5+ = 23.9%) and obese (21.9%) groups consumed significantly less FV than the normal-weight (27.4%) group (p < 0.0001). This inverse association remained significant even after controlling for potential confounding factors. Multivariate analysis identified five significant moderators (p < 0.0001) after controlling for all evaluated variables: race, sex, smoking status, health coverage, and physical activity. Notably, physically inactive obese males tended to consume the least FV (% FV5+ = 14.7%). Conclusion Current US population FV intake level is below recommended levels. The inverse association between FV intake and obesity was significant and was moderated by demographic, socioeconomic status, and lifestyle factors. These factors should be considered when developing policies and interventions to increase FV intake. PMID:22248995

Design Issues in Small-Area Studies of Environment and Health

PubMed Central

Elliott, Paul; Savitz, David A.

2008-01-01

Background Small-area studies are part of the tradition of spatial epidemiology, which is concerned with the analysis of geographic patterns of disease with respect to environmental, demographic, socioeconomic, and other factors. We focus on etiologic research, where the aim is to make inferences about spatially varying environmental factors influencing the risk of disease. Methods and results We illustrate the approach through three exemplars: a) magnetic fields from overhead electric power lines and the occurrence of childhood leukemia, which illustrates the use of geographic information systems to focus on areas with high exposure prevalence; b) drinking-water disinfection by-products and reproductive outcomes, taking advantage of large between- to within-area variability in exposures from the water supply; and c) chronic exposure to air pollutants and cardiorespiratory health, where issues of socioeconomic confounding are particularly important. Discussion The small-area epidemiologic approach assigns exposure estimates to individuals based on location of residence or other geographic variables such as workplace or school. In this way, large populations can be studied, increasing the ability to investigate rare exposures or rare diseases. The approach is most effective when there is well-defined exposure variation across geographic units, limited within-area variation, and good control for potential confounding across areas. Conclusions In conjunction with traditional individual-based approaches, small-area studies offer a valuable addition to the armamentarium of the environmental epidemiologist. Modeling of exposure patterns coupled with collection of individual-level data on subsamples of the population should lead to improved risk estimates (i.e., less potential for bias) and help strengthen etiologic inference. PMID:18709174

Type and Timing of Menopause and Later Life Mortality Among Women in the Iowa Established Populations for the Epidemiological Study of the Elderly Cohort

PubMed Central

Cooper, Rachel; Wallace, Robert B.; Guralnik, Jack M.

2012-01-01

Abstract Background The relationship between menopausal characteristics and later life mortality is unclear. We tested the hypotheses that women with surgical menopause would have increased all-cause and cardiovascular mortality compared with women with natural menopause, and that women with earlier ages at natural or surgical menopause would have greater all-cause and cardiovascular mortality than women with later ages at menopause. Methods Women who participated in the Iowa cohort of the Established Populations for the Epidemiologic Study of the Elderly (n=1684) reported menopausal characteristics and potential confounding variables at baseline and were followed up for up to 24 years. Participants were aged 65 years or older at baseline and lived in rural areas. We used survival analysis to examine the relationships between menopausal characteristics and all-cause and cardiovascular mortality. Results A total of 1477 women (87.7% of respondents) died during the study interval. Women with an age at natural menopause ≥55 years had increased all-cause and cardiovascular disease mortality compared with women who had natural menopause at younger ages. Type of menopause and age at surgical menopause were not related to mortality. These patterns persisted after adjustment for potential confounding variables. Conclusions Among an older group of women from a rural area of the United States, later age at natural menopause was related to increased all-cause and cardiovascular mortality. Monitoring the cardiovascular health of this group of older women may contribute to improved survival times. PMID:21970557

Role of Body Mass Index and Gestational Weight Gain in Breastfeeding Outcomes

PubMed Central

Schaefer, Eric W.; Beiler, Jessica S.; Paul, Ian M.

2012-01-01

Abstract Objective This study determined whether high maternal prepregnancy body mass index (BMI) and/or excess gestational weight gain (GWG) is associated with reduced breastfeeding duration and earlier formula supplementation. Study Design A prospective longitudinal cohort of postpartum women (n=718), who were a subset of a larger randomized trial, was followed for 6 months postdelivery. We evaluated the relationship between BMI or BMI/GWG groups and timing of breastfeeding cessation and introduction of formula using Kaplan–Meier curves and log-rank tests. Then, we used multivariable Cox proportional hazards models to evaluate the relationship between BMI and BMI/GWG on these breastfeeding outcomes after controlling for potential confounding variables. Results The expected relationships between high BMI and high BMI/GWG and poor breastfeeding outcomes were observed in Kaplan–Meier curves. However, after adjusting for relevant maternal and infant covariates in the Cox models, the differences became nonsignificant. Prepregnancy BMI category was not statistically associated with breastfeeding duration (p=0.06) or timing of formula introduction (p=0.15). Similarly, BMI and GWG in combination were not associated with duration (p=0.33) or timing of formula introduction (p=0.18). Mothers' intended breastfeeding duration and rating of the importance of breastfeeding remained the only significant modifiable predictors of breastfeeding outcomes in the final models. Conclusions Maternal BMI and GWG were not significantly associated with breastfeeding outcomes after adjusting for confounding variables. Mothers' plans for breastfeeding duration and the importance mothers assign to breastfeeding remain the optimal intervention points for lengthening breastfeeding duration and reducing formula supplementation. PMID:23215909

Environmental confounding in gene-environment interaction studies.

PubMed

Vanderweele, Tyler J; Ko, Yi-An; Mukherjee, Bhramar

2013-07-01

We show that, in the presence of uncontrolled environmental confounding, joint tests for the presence of a main genetic effect and gene-environment interaction will be biased if the genetic and environmental factors are correlated, even if there is no effect of either the genetic factor or the environmental factor on the disease. When environmental confounding is ignored, such tests will in fact reject the joint null of no genetic effect with a probability that tends to 1 as the sample size increases. This problem with the joint test vanishes under gene-environment independence, but it still persists if estimating the gene-environment interaction parameter itself is of interest. Uncontrolled environmental confounding will bias estimates of gene-environment interaction parameters even under gene-environment independence, but it will not do so if the unmeasured confounding variable itself does not interact with the genetic factor. Under gene-environment independence, if the interaction parameter without controlling for the environmental confounder is nonzero, then there is gene-environment interaction either between the genetic factor and the environmental factor of interest or between the genetic factor and the unmeasured environmental confounder. We evaluate several recently proposed joint tests in a simulation study and discuss the implications of these results for the conduct of gene-environment interaction studies.

Negative control exposure studies in the presence of measurement error: implications for attempted effect estimate calibration.

PubMed

Sanderson, Eleanor; Macdonald-Wallis, Corrie; Davey Smith, George

2018-04-01

Negative control exposure studies are increasingly being used in epidemiological studies to strengthen causal inference regarding an exposure-outcome association when unobserved confounding is thought to be present. Negative control exposure studies contrast the magnitude of association of the negative control, which has no causal effect on the outcome but is associated with the unmeasured confounders in the same way as the exposure, with the magnitude of the association of the exposure with the outcome. A markedly larger effect of the exposure on the outcome than the negative control on the outcome strengthens inference that the exposure has a causal effect on the outcome. We investigate the effect of measurement error in the exposure and negative control variables on the results obtained from a negative control exposure study. We do this in models with continuous and binary exposure and negative control variables using analysis of the bias of the estimated coefficients and Monte Carlo simulations. Our results show that measurement error in either the exposure or negative control variables can bias the estimated results from the negative control exposure study. Measurement error is common in the variables used in epidemiological studies; these results show that negative control exposure studies cannot be used to precisely determine the size of the effect of the exposure variable, or adequately adjust for unobserved confounding; however, they can be used as part of a body of evidence to aid inference as to whether a causal effect of the exposure on the outcome is present.

Gender effects in gaming research: a case for regression residuals?

PubMed

Pfister, Roland

2011-10-01

Numerous recent studies have examined the impact of video gaming on various dependent variables, including the players' affective reactions, positive as well as detrimental cognitive effects, and real-world aggression. These target variables are typically analyzed as a function of game characteristics and player attributes-especially gender. However, findings on the uneven distribution of gaming experience between males and females, on the one hand, and the effect of gaming experience on several target variables, on the other hand, point at a possible confound when gaming experiments are analyzed with a standard analysis of variance. This study uses simulated data to exemplify analysis of regression residuals as a potentially beneficial data analysis strategy for such datasets. As the actual impact of gaming experience on each of the various dependent variables differs, the ultimate benefits of analysis of regression residuals entirely depend on the research question, but it offers a powerful statistical approach to video game research whenever gaming experience is a confounding factor.

Breath biomarkers for lung cancer detection and assessment of smoking related effects--confounding variables, influence of normalization and statistical algorithms.

PubMed

Kischkel, Sabine; Miekisch, Wolfram; Sawacki, Annika; Straker, Eva M; Trefz, Phillip; Amann, Anton; Schubert, Jochen K

2010-11-11

Up to now, none of the breath biomarkers or marker sets proposed for cancer recognition has reached clinical relevance. Possible reasons are the lack of standardized methods of sampling, analysis and data processing and effects of environmental contaminants. Concentration profiles of endogenous and exogenous breath markers were determined in exhaled breath of 31 lung cancer patients, 31 smokers and 31 healthy controls by means of SPME-GC-MS. Different correcting and normalization algorithms and a principal component analysis were applied to the data. Differences of exhalation profiles in cancer and non-cancer patients did not persist if physiology and confounding variables were taken into account. Smoking history, inspired substance concentrations, age and gender were recognized as the most important confounding variables. Normalization onto PCO2 or BSA or correction for inspired concentrations only partially solved the problem. In contrast, previous smoking behaviour could be recognized unequivocally. Exhaled substance concentrations may depend on a variety of parameters other than the disease under investigation. Normalization and correcting parameters have to be chosen with care as compensating effects may be different from one substance to the other. Only well-founded biomarker identification, normalization and data processing will provide clinically relevant information from breath analysis. 2010 Elsevier B.V. All rights reserved.

PHOSPHATE BINDER USE AND MORTALITY AMONG HEMODIALYSIS PATIENTS IN THE DOPPS: EVALUATION OF POSSIBLE CONFOUNDING BY NUTRITIONAL STATUS

PubMed Central

Lopes, Antonio Alberto; Tong, Lin; Thumma, Jyothi; Li, Yun; Fuller, Douglas S.; Morgenstern, Hal; Bommer, Jürgen; Kerr, Peter G; Tentori, Francesca; Akiba, Takashi; Gillespie, Brenda; Robinson, Bruce M.; Port, Friedrich K; Pisoni, Ronald L.

2014-01-01

Background Poor nutritional status and both hyperphosphatemia and hypophosphatemia are associated with increased mortality in maintenance hemodialysis (MHD) patients. We assessed associations of PB prescription with survival and indicators of nutritional status among (MHD) patients. Study Design Prospective cohort study (DOPPS) 1996 to 2008. Setting and Participants 23,898 MHD patients at 923 facilities in 12 countries. Predictors Patient-level PB prescription; and case-mix-adjusted facility percentage PB prescription using an instrumental-variable analysis. Outcome All-cause mortality. Results Overall, 88% of patients were prescribed PBs. The distributions of age, comorbidities and other characteristics showed small differences between facilities with higher and lower percentage PB prescription. Patient-level PB prescription was strongly associated at baseline with indicators of better nutrition, i.e., higher serum creatinine, albumin, normalized protein-catabolic rate, BMI and absence of cachectic appearance. Overall, patients prescribed PBs displayed 25% lower mortality (hazard ratio [HR] = 0.75, 95% confidence interval [CI] = 0.68–0.83) when adjusted for serum phosphorus and other covariates; further adjustment for nutritional indicators attenuated this association (HR = 0.88, 95% CI = 0.80–0.97). This inverse association, however, was observed only for patients with serum phosphorus ≥3.5mg/dL. In the instrumental-variable analysis, case-mix-adjusted facility percentage PB prescription (range: 23–100%) was positively associated with better nutritional status and inversely associated with mortality (HR for 10% more PB = 0.93, 95% CI = 0.89–0.96). Further adjustment for nutritional indicators reduced this association to HR = 0.95 (95% CI = 0.92–0.99). Limitations Results were based on PB prescription; PB and nutritional data were cross-sectional; dietary restriction was not assessed; observational design limits causal inference due to possible residual confounding. Conclusions Longer survival and better nutritional status were observed for MHD patients prescribed PBs and in facilities with greater percentage PB prescription. Understanding the mechanisms for explaining this effect and ruling out possible residual confounding require additional research. PMID:22385781

Relative importance of climatic, geographic and socio-economic determinants of malaria in Malawi

PubMed Central

2013-01-01

Background Malaria transmission is influenced by variations in meteorological conditions, which impact the biology of the parasite and its vector, but also socio-economic conditions, such as levels of urbanization, poverty and education, which impact human vulnerability and vector habitat. The many potential drivers of malaria, both extrinsic, such as climate, and intrinsic, such as population immunity are often difficult to disentangle. This presents a challenge for the modelling of malaria risk in space and time. Methods A statistical mixed model framework is proposed to model malaria risk at the district level in Malawi, using an age-stratified spatio-temporal dataset of malaria cases from July 2004 to June 2011. Several climatic, geographic and socio-economic factors thought to influence malaria incidence were tested in an exploratory model. In order to account for the unobserved confounding factors that influence malaria, which are not accounted for using measured covariates, a generalized linear mixed model was adopted, which included structured and unstructured spatial and temporal random effects. A hierarchical Bayesian framework using Markov chain Monte Carlo simulation was used for model fitting and prediction. Results Using a stepwise model selection procedure, several explanatory variables were identified to have significant associations with malaria including climatic, cartographic and socio-economic data. Once intervention variations, unobserved confounding factors and spatial correlation were considered in a Bayesian framework, a final model emerged with statistically significant predictor variables limited to average precipitation (quadratic relation) and average temperature during the three months previous to the month of interest. Conclusions When modelling malaria risk in Malawi it is important to account for spatial and temporal heterogeneity and correlation between districts. Once observed and unobserved confounding factors are allowed for, precipitation and temperature in the months prior to the malaria season of interest are found to significantly determine spatial and temporal variations of malaria incidence. Climate information was found to improve the estimation of malaria relative risk in 41% of the districts in Malawi, particularly at higher altitudes where transmission is irregular. This highlights the potential value of climate-driven seasonal malaria forecasts. PMID:24228784

Long-Term Neurotoxic Effects of Early Life Exposure to Tetrachloroethylene-contaminated Drinking Water

PubMed Central

Aschengrau, Ann; Janulewicz, Patricia A.; White, Roberta F.; Vieira, Veronica M.; Gallagher, Lisa G.; Getz, Kelly D.; Webster, Thomas F.; Ozonoff, David M.

2016-01-01

Background Tetrachloroethene (PCE) is a common environmental and occupational contaminant and an acknowledged neurotoxicant. From 1968 through 1983 widespread contamination of public drinking water supplies with PCE occurred in the Cape Cod region of Massachusetts. The source of the contamination was a vinyl liner applied to the inner surface of water distribution pipes. Objectives A retrospective cohort study (“the Cape Cod Health Study”) was undertaken to examine possible health consequences of early life exposure to PCE-contaminated drinking water. This review describes the study methods and findings regarding the impact of prenatal and childhood exposure on neurological outcomes during early adulthood, including vision, neuropsychological functioning, brain structure, risky behaviors, and mental illness. The review also describes the strengths and challenges of conducting population-based epidemiological research in this unique setting. Methods Subjects were identified by cross-matching birth certificate and water system data. Information on health outcomes and confounding variables was collected from self-administered surveys (N= 1,689), neuropsychological tests (N=63), vision exam (N=63), and magnetic resonance imaging (N=42). Early life exposure to PCE was estimated using a leaching and transport model. The data analysis compared the occurrence of each health outcome among subjects with prenatal and early childhood PCE exposure to unexposed subjects while considering the impact of confounding variables. Results The study found evidence that early life exposure to PCE-contaminated drinking water has long-term neurotoxic effects. The strongest associations were seen with illicit drug use, bipolar disorder, and post-traumatic stress disorder. Key strengths of the study were availability of historical data on affected water systems, a relatively high exposure prevalence and wide range of exposure levels, and little confounding. Challenges arose mainly from the historical nature of the exposure assessments. Conclusions The Cape Cod Health Study demonstrates how scientists can take advantage of unique “natural experiments” to learn about the health effects of environmental pollution. This body of work has improved our understanding of the long-term health effects of early life exposure to this common environmental contaminant and will help risk assessors and policy makers ensure that U.S. drinking water supplies are safe for vulnerable populations. PMID:27325074

Influence of lifestyle and genetic variants in the aldo-keto reductase 1C3 rs12529 polymorphism in high-risk prostate cancer detection variability assessed between US and New Zealand cohorts

PubMed Central

Ambs, Stefan; Tang, Wei; Zhu, Shuotun; Dorsey, Tiffany H.; Goudie, Megan; Masters, Jonathan G.; Ferguson, Lynnette R.

2018-01-01

Introduction The prostate-specific antigen (PSA) based prostate cancer (PC) screening is currently being debated. The current assessment is to understand the variability of detecting high-risk PC in a NZ cohort in comparison to a US cohort with better PSA screening facilities. Aldo-keto reductase 1C3 (AKR1C3) is known for multiple functions with a potential to regulate subsequent PSA levels. Therefore, we wish to understand the influence of tobacco smoking and the AKR1C3 rs12529 gene polymorphism in this variability. Method NZ cohort (n = 376) consisted of 94% Caucasians while the US cohort consisted of African Americans (AA), n = 202, and European Americans (EA), n = 232. PSA level, PC grade and stage at diagnosis were collected from hospital databases for assigning high-risk PC status. Tobacco smoking status and the AKR1C3 rs12529 SNP genotype were considered as confounding variables. Variation of the cumulative % high-risk PC (outcome variable) with increasing PSA intervals (exposure factor) was compared between the cohorts using the Kolmogorov-Smirnov test. Comparisons were carried out with and without stratifications made using confounding variables. Results NZ cohort has been diagnosed at a significantly higher mean age (66.67± (8.08) y) compared to both AA (62.65±8.17y) and EA (64.83+8.56y); median PSA (NZ 8.90ng/ml compared to AA 6.86ng/ml and EA 5.80ng/ml); and Gleason sum (NZ (7) compared EA (6)) (p<0.05). The cumulative % high-risk PC detection shows NZ cohort with a significantly lower diagnosis rates at PSA levels between >6 - <10ng/ml compared to both US groups (p<0.05). These were further compounded significantly by smoking status and genetics. Conclusions High-risk PCs recorded at higher PSA levels in NZ could be due to factors including lower levels of PSA screening and subsequent specialist referrals for biopsies. These consequences could be pronounced among NZ ever smokers carrying the AKR1C3 rs12529 G alleles making them a group that requires increased PSA screening attention. PMID:29920533

Fatigue and crashes: the case of freight transport in Colombia.

PubMed

Torregroza-Vargas, Nathaly M; Bocarejo, Juan Pablo; Ramos-Bonilla, Juan P

2014-11-01

Truck drivers have been involved in a significant number of road fatalities in Colombia. To identify variables that could be associated with crashes in which truck drivers are involved, a logistic regression model was constructed. The model had as the response variable a dichotomous variable that included the presence or absence of a crash during a specific trip. As independent variables the model included information regarding a driver's work shift, with variables that could be associated with driver's fatigue. The model also included potential confounders related with road conditions. With the model, it was possible to determine the odds ratio of a crash in relation to several variables, adjusting for confounding. To collect the information about the trips included in the model, a survey among truck drivers was conducted. The results suggest strong associations between crashes (i.e., some of them statistically significant) with the number of stops made during the trip, and the average time of each stop. Survey analysis allowed us to identify the practices that contribute to generating fatigue and unhealthy conditions on the road among professional drivers. A review of national regulations confirmed the lack of legislation on this topic. Copyright © 2014 Elsevier Ltd. All rights reserved.

The epidemiology of bovine respiratory disease: What is the evidence for preventive measures?

PubMed Central

Taylor, Jared D.; Fulton, Robert W.; Lehenbauer, Terry W.; Step, Douglas L.; Confer, Anthony W.

2010-01-01

Bovine respiratory disease (BRD) is the most common and costly disease of beef cattle in North America. Despite extensive research, industry practices are often more informed by dogma than by fact. Frequently advocated interventions, including vaccination, various processing procedures, and nutritional manipulation, have limited impact on morbidity and mortality. Evidence for use of oral antimicrobials, either in feed or water, appears to be equivocal. In contrast, preconditioning and metaphylaxis have significant scientific evidence of efficacy, with weaning prior to sale potentially being the most important component of preconditioning. The inability to reach more definitive conclusions in preventing BRD may be attributable to difficulties in investigating the disease. Study challenges include potential for extensive confounding, tremendous variability, the multi-factorial nature of the disease, and inadequate methods for diagnosis. PMID:21358927

Efficient estimation of the attributable fraction when there are monotonicity constraints and interactions.

PubMed

Traskin, Mikhail; Wang, Wei; Ten Have, Thomas R; Small, Dylan S

2013-01-01

The PAF for an exposure is the fraction of disease cases in a population that can be attributed to that exposure. One method of estimating the PAF involves estimating the probability of having the disease given the exposure and confounding variables. In many settings, the exposure will interact with the confounders and the confounders will interact with each other. Also, in many settings, the probability of having the disease is thought, based on subject matter knowledge, to be a monotone increasing function of the exposure and possibly of some of the confounders. We develop an efficient approach for estimating logistic regression models with interactions and monotonicity constraints, and apply this approach to estimating the population attributable fraction (PAF). Our approach produces substantially more accurate estimates of the PAF in some settings than the usual approach which uses logistic regression without monotonicity constraints.

The High Prevalence of Incarceration History Among Black Men Who Have Sex With Men in the United States: Associations and Implications

PubMed Central

Magnus, Manya; Kuo, Irene; Wang, Lei; Liu, Ting-Yuan; Mayer, Kenneth H.

2014-01-01

Objectives. We examined lifetime incarceration history and its association with key characteristics among 1553 Black men who have sex with men (BMSM) recruited in 6 US cities. Methods. We conducted bivariate analyses of data collected from the HIV Prevention Trials Network 061 study from July 2009 through December 2011 to examine the relationship between incarceration history and demographic and psychosocial variables predating incarceration and multivariate logistic regression analyses to explore the associations between incarceration history and demographic and psychosocial variables found to be significant. We then used multivariate logistic regression models to explore the independent association between incarceration history and 6 outcome variables. Results. After adjusting for confounders, we found that increasing age, transgender identity, heterosexual or straight identity, history of childhood violence, and childhood sexual experience were significantly associated with incarceration history. A history of incarceration was also independently associated with any alcohol and drug use in the past 6 months. Conclusions. The findings highlight an elevated lifetime incarceration history among a geographically diverse sample of BMSM and the need to adequately assess the impact of incarceration among BMSM in the United States. PMID:24432948

Disease Risk Score (DRS) as a Confounder Summary Method: Systematic Review and Recommendations

PubMed Central

Tadrous, Mina; Gagne, Joshua J.; Stürmer, Til; Cadarette, Suzanne M.

2013-01-01

Purpose To systematically examine trends and applications of the disease risk score (DRS) as a confounder summary method. Methods We completed a systematic search of MEDLINE and Web of Science® to identify all English language articles that applied DRS methods. We tabulated the number of publications by year and type (empirical application, methodological contribution, or review paper) and summarized methods used in empirical applications overall and by publication year (<2000, ≥2000). Results Of 714 unique articles identified, 97 examined DRS methods and 86 were empirical applications. We observed a bimodal distribution in the number of publications over time, with a peak 1979-1980, and resurgence since 2000. The majority of applications with methodological detail derived DRS using logistic regression (47%), used DRS as a categorical variable in regression (93%), and applied DRS in a non-experimental cohort (47%) or case-control (42%) study. Few studies examined effect modification by outcome risk (23%). Conclusion Use of DRS methods has increased yet remains low. Comparative effectiveness research may benefit from more DRS applications, particularly to examine effect modification by outcome risk. Standardized terminology may facilitate identification, application, and comprehension of DRS methods. More research is needed to support the application of DRS methods, particularly in case-control studies. PMID:23172692

Prospective Association Between Negative Life Events and Initiation of Sexual Intercourse: The Influence of Family Structure and Family Income

PubMed Central

Oman, Roy F.; Vesely, Sara K.; Aspy, Cheryl B.; Tolma, Eleni L.; John, Robert

2015-01-01

Objectives. We examined the prospective association between negative life events and time to initiation of sexual intercourse and the influence of family structure and family income on this association. Methods. We followed up a randomly selected sample (n = 649) of ethnically diverse parents and their children aged 12 to 17 years over a 5-year period. We conducted Cox proportional hazards regression analysis to examine the relation between negative life events and time to initiation of sexual intercourse. Family structure and family income were assessed as confounders. Results. Negative life events were significant predictors of time to initiation of sexual intercourse in adolescents. After controlling for demographic variables, youths reporting 1 negative life event had a hazard of initiation of sexual intercourse 1.40 times greater and youths reporting 2 or more negative life events had a hazard of initiation of sexual intercourse 1.61 times greater compared with youths reporting no negative life events. Family structure and family income were not significant confounders of the relation between initiation of sexual intercourse and negative life events. Conclusions. Interventions to prevent initiation of sexual intercourse should focus on youths with recent negative life events, regardless of family income and structure. PMID:25602885

THE EXPERIMENTAL DESIGN FOR BeO IRAADIATION EXPERIMENTS ORNL 41-8 AND ORNL 41-9

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gardiner, D.A.

1962-07-18

The experimental plan for irradiating BeO pellets in Experiments ORNL 41- 8 and ORNL 41-9 was chosen in accordance with the principles of experimental design. The design is known by statisticians as a 2/sup 5/ factorial experiment confound'' in six replications. Five variables---size, density, grain size, temperature and time--are controlled at two levels to form the basic 2i factorial experiment. The sixth variable, neutron flux, is introduced by confounding on higher-order interactions. An explanation is presented in nontechnical language the means by which the aims of the experimenters and the physical conditions affecting the experiment were utilized in constructing themore » experimental design. (auth)« less

The Conservative Corner of the Liberal Academy? Fraternity/Sorority Membership, Politics, and Activism

ERIC Educational Resources Information Center

Hevel, Michael S.; Weeden, Dustin D.; Pasquesi, Kira; Pascarella, Ernest T.

2015-01-01

We use a longitudinal dataset to explore the effect of fraternity/sorority membership on political orientation and social/political activism. After controlling for a variety of potentially confounding variables, including pretests on the dependent variables, fraternity and sorority members were significantly less liberal that their unaffiliated…

Beyond Free Lunch: Which Family Background Measures Matter?

ERIC Educational Resources Information Center

Lubienski, Sarah Theule; Crane, Corinna Crawford

2010-01-01

Most studies of school achievement use free-lunch eligibility or other basic indicators to adjust for differences in students' socioeconomic backgrounds. This study determines whether these variables are enough to separate the confounding effects of students' backgrounds from the main variables of interest in education studies. The Early Childhood…

Fusing Data Mining, Machine Learning and Traditional Statistics to Detect Biomarkers Associated with Depression

PubMed Central

Dipnall, Joanna F.

2016-01-01

Background Atheoretical large-scale data mining techniques using machine learning algorithms have promise in the analysis of large epidemiological datasets. This study illustrates the use of a hybrid methodology for variable selection that took account of missing data and complex survey design to identify key biomarkers associated with depression from a large epidemiological study. Methods The study used a three-step methodology amalgamating multiple imputation, a machine learning boosted regression algorithm and logistic regression, to identify key biomarkers associated with depression in the National Health and Nutrition Examination Study (2009–2010). Depression was measured using the Patient Health Questionnaire-9 and 67 biomarkers were analysed. Covariates in this study included gender, age, race, smoking, food security, Poverty Income Ratio, Body Mass Index, physical activity, alcohol use, medical conditions and medications. The final imputed weighted multiple logistic regression model included possible confounders and moderators. Results After the creation of 20 imputation data sets from multiple chained regression sequences, machine learning boosted regression initially identified 21 biomarkers associated with depression. Using traditional logistic regression methods, including controlling for possible confounders and moderators, a final set of three biomarkers were selected. The final three biomarkers from the novel hybrid variable selection methodology were red cell distribution width (OR 1.15; 95% CI 1.01, 1.30), serum glucose (OR 1.01; 95% CI 1.00, 1.01) and total bilirubin (OR 0.12; 95% CI 0.05, 0.28). Significant interactions were found between total bilirubin with Mexican American/Hispanic group (p = 0.016), and current smokers (p<0.001). Conclusion The systematic use of a hybrid methodology for variable selection, fusing data mining techniques using a machine learning algorithm with traditional statistical modelling, accounted for missing data and complex survey sampling methodology and was demonstrated to be a useful tool for detecting three biomarkers associated with depression for future hypothesis generation: red cell distribution width, serum glucose and total bilirubin. PMID:26848571

Phenology and growth adjustments of oil palm (Elaeis guineensis) to photoperiod and climate variability

PubMed Central

Legros, S.; Mialet-Serra, I.; Caliman, J.-P.; Siregar, F. A.; Clément-Vidal, A.; Dingkuhn, M.

2009-01-01

Background and Aims Oil palm flowering and fruit production show seasonal maxima whose causes are unknown. Drought periods confound these rhythms, making it difficult to analyse or predict dynamics of production. The present work aims to analyse phenological and growth responses of adult oil palms to seasonal and inter-annual climatic variability. Methods Two oil palm genotypes planted in a replicated design at two sites in Indonesia underwent monthly observations during 22 months in 2006–2008. Measurements included growth of vegetative and reproductive organs, morphology and phenology. Drought was estimated from climatic water balance (rainfall – potential evapotranspiration) and simulated fraction of transpirable soil water. Production history of the same plants for 2001–2005 was used for inter-annual analyses. Key Results Drought was absent at the equatorial Kandista site (0°55′N) but the Batu Mulia site (3°12′S) had a dry season with variable severity. Vegetative growth and leaf appearance rate fluctuated with drought level. Yield of fruit, a function of the number of female inflorescences produced, was negatively correlated with photoperiod at Kandista. Dual annual maxima were observed supporting a recent theory of circadian control. The photoperiod-sensitive phases were estimated at 9 (or 9 + 12 × n) months before bunch maturity for a given phytomer. The main sensitive phase for drought effects was estimated at 29 months before bunch maturity, presumably associated with inflorescence sex determination. Conclusion It is assumed that seasonal peaks of flowering in oil palm are controlled even near the equator by photoperiod response within a phytomer. These patterns are confounded with drought effects that affect flowering (yield) with long time-lag. Resulting dynamics are complex, but if the present results are confirmed it will be possible to predict them with models. PMID:19748909

The Causal Mediation Formula - A Guide to the Assessment of Pathways and Mechanisms

DTIC Science & Technology

2011-10-01

for estimating CDE(z) in observational studies (in the presence of unobserved confounders) can be derived using do- calculus (Pearl, 2009, pp. 85–88...2011; Albert and Nelson , 2011). 7In the presence of measured and unmeasured confounders, the general conditions under which NDE is estimable from...achieve this independence (see footnote 7), that Z may represent a vector of variables, and that integrals should replace summations when dealing with

Measuring the surgical 'learning curve': methods, variables and competency.

PubMed

Khan, Nuzhath; Abboudi, Hamid; Khan, Mohammed Shamim; Dasgupta, Prokar; Ahmed, Kamran

2014-03-01

To describe how learning curves are measured and what procedural variables are used to establish a 'learning curve' (LC). To assess whether LCs are a valuable measure of competency. A review of the surgical literature pertaining to LCs was conducted using the Medline and OVID databases. Variables should be fully defined and when possible, patient-specific variables should be used. Trainee's prior experience and level of supervision should be quantified; the case mix and complexity should ideally be constant. Logistic regression may be used to control for confounding variables. Ideally, a learning plateau should reach a predefined/expert-derived competency level, which should be fully defined. When the group splitting method is used, smaller cohorts should be used in order to narrow the range of the LC. Simulation technology and competence-based objective assessments may be used in training and assessment in LC studies. Measuring the surgical LC has potential benefits for patient safety and surgical education. However, standardisation in the methods and variables used to measure LCs is required. Confounding variables, such as participant's prior experience, case mix, difficulty of procedures and level of supervision, should be controlled. Competency and expert performance should be fully defined. © 2013 The Authors. BJU International © 2013 BJU International.

Combining fixed effects and instrumental variable approaches for estimating the effect of psychosocial job quality on mental health: evidence from 13 waves of a nationally representative cohort study.

PubMed

Milner, Allison; Aitken, Zoe; Kavanagh, Anne; LaMontagne, Anthony D; Pega, Frank; Petrie, Dennis

2017-06-23

Previous studies suggest that poor psychosocial job quality is a risk factor for mental health problems, but they use conventional regression analytic methods that cannot rule out reverse causation, unmeasured time-invariant confounding and reporting bias. This study combines two quasi-experimental approaches to improve causal inference by better accounting for these biases: (i) linear fixed effects regression analysis and (ii) linear instrumental variable analysis. We extract 13 annual waves of national cohort data including 13 260 working-age (18-64 years) employees. The exposure variable is self-reported level of psychosocial job quality. The instruments used are two common workplace entitlements. The outcome variable is the Mental Health Inventory (MHI-5). We adjust for measured time-varying confounders. In the fixed effects regression analysis adjusted for time-varying confounders, a 1-point increase in psychosocial job quality is associated with a 1.28-point improvement in mental health on the MHI-5 scale (95% CI: 1.17, 1.40; P < 0.001). When the fixed effects was combined with the instrumental variable analysis, a 1-point increase psychosocial job quality is related to 1.62-point improvement on the MHI-5 scale (95% CI: -0.24, 3.48; P = 0.088). Our quasi-experimental results provide evidence to confirm job stressors as risk factors for mental ill health using methods that improve causal inference. © The Author 2017. Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Francisco Bay estuarine system

USGS Publications Warehouse

Cloern, J.E.; Canuel, E.A.; Harris, D.

2002-01-01

We report measurements of seasonal variability in the C-N stable isotope ratios of plants collected across the habitat mosaic of San Francisco Bay, its marshes, and its tributary river system. Analyses of 868 plant samples were binned into 10 groups (e.g., terrestrial riparian, freshwater phytoplankton, salt marsh) to determine whether C-N isotopes can be used as biomarkers for tracing the origins of organic matter in this river-marsh-estuary complex. Variability of ??13C and ??15N was high (???5-10???) within each plant group, and we identified three modes of variability: (1) between species and their microhabitats, (2) over annual cycles of plant growth and senescence, and (3) between living and decomposing biomass. These modes of within-group variability obscure any source-specific isotopic signatures, confounding the application of C-N isotopes for identifying the origins of organic matter. A second confounding factor was large dissimilarity between the ??13C-??15N of primary producers and the organic-matter pools in the seston and sediments. Both confounding factors impede the application of C-N isotopes to reveal the food supply to primary consumers in ecosystems supporting diverse autotrophs and where the isotopic composition of organic matter has been transformed and become distinct from that of its parent plant sources. Our results support the advice of others: variability of C-N stable isotopes within all organic-matter pools is high and must be considered in applications of these isotopes to trace trophic linkages from primary producers to primary consumers. Isotope-based approaches are perhaps most powerful when used to complement other tools, such as molecular biomarkers, bioassays, direct measures of production, and compilations of organic-matter budgets.

Spatial variation in mortality risk for haematological malignancies near a petrochemical refinery: a population-based case-control study

PubMed Central

Di Salvo, Francesca; Meneghini, Elisabetta; Vieira, Veronica; Baili, Paolo; Mariottini, Mauro; Baldini, Marco; Micheli, Andrea; Sant, Milena

2015-01-01

Introduction The study investigated the geographic variation of mortality risk for hematological malignancies (HMs) in order to identify potential high-risk areas near an Italian petrochemical refinery. Material and methods A population-based case-control study was conducted and residential histories for 171 cases and 338 sex- and age-matched controls were collected. Confounding factors were obtained from interviews with consenting relatives for 109 HM deaths and 267 controls. To produce risk mortality maps, two different approaches were applied. We mapped (1) adptive kernel density relative risk estimation (KDE) for case-control studies which estimates a spatial relative risk function using the ratio between cases and controls’ densities, and (2) estimated odds ratios for case-control study data using generalized additive models (GAMs) to smooth the effect of location, a proxy for exposure, while adjusting for confounding variables. Results No high-risk areas for HM mortality were identified among all subjects (men and women combined), by applying both approaches. Using the adaptive KDE approach, we found a significant increase in death risk only among women in a large area 2–6 km southeast of the refinery and the application of GAMs also identified a similarly-located significant high-risk area among women only (global p-value<0.025). Potential confounding risk factors we considered in the GAM did not alter the results. Conclusion Both approaches identified a high-risk area close to the refinery among women only. Those spatial methods are useful tools for public policy management to determine priority areas for intervention. Our findings suggest several directions for further research in order to identify other potential environmental exposures that may be assessed in forthcoming studies based on detailed exposure modeling. PMID:26073202

Adherence to placebo and mortality in the Beta Blocker Evaluation of Survival Trial (BEST)

PubMed Central

Pressman, Alice; Avins, Andrew L.; Neuhaus, John; Ackerson, Lynn; Rudd, Peter

2012-01-01

Background Randomized controlled trials have reported lower mortality among patients who adhere to placebo compared with those who do not. We explored this phenomenon by reanalyzing data from the placebo arm of the Beta Blocker Evaluation of Survival Trial (BEST), a randomized, double-blind, placebo-controlled trial of bucindolol and mortality. Aims Our primary aim was to measure and explain the association between adherence to placebo and total mortality among the placebo-allocated participants in the BEST trial. Secondary aims included assessment of the association between placebo adherence and cause-specific mortality. Methods Participants with "higher placebo adherence" were defined as having taken at least 75% of their placebo study medication over the entire course of each individual’s participation in the study, while those with “lower placebo adherence” took <75%. Primary outcome was in-study all-cause mortality. To account for confounding, we adjusted for all available modifiable, non-modifiable and psychosocial variables. Results Adherent participants had a significantly lower total mortality compared to less-adherent participants (HR = 0.61, 95% Confidence Interval: 0.46–0.82). Adjusting for available confounders did not change the magnitude or significance of the estimates. When considering cause-specific mortality, CVD and pump failure showed similar associations. Conclusions Analyses of the BEST trial data support a strong association between adherence to placebo study medication and total mortality. While probably not due to publication bias or simple confounding by healthy lifestyle factors, the underlying explanation for the association remains a mystery. Prospective examination of this association is necessary to better understand the underlying mechanism of this observation. PMID:22265975

Identifying cis-mediators for trans-eQTLs across many human tissues using genomic mediation analysis

PubMed Central

Yang, Fan; Wang, Jiebiao; Pierce, Brandon L.; Chen, Lin S.

2017-01-01

The impact of inherited genetic variation on gene expression in humans is well-established. The majority of known expression quantitative trait loci (eQTLs) impact expression of local genes (cis-eQTLs). More research is needed to identify effects of genetic variation on distant genes (trans-eQTLs) and understand their biological mechanisms. One common trans-eQTLs mechanism is “mediation” by a local (cis) transcript. Thus, mediation analysis can be applied to genome-wide SNP and expression data in order to identify transcripts that are “cis-mediators” of trans-eQTLs, including those “cis-hubs” involved in regulation of many trans-genes. Identifying such mediators helps us understand regulatory networks and suggests biological mechanisms underlying trans-eQTLs, both of which are relevant for understanding susceptibility to complex diseases. The multitissue expression data from the Genotype-Tissue Expression (GTEx) program provides a unique opportunity to study cis-mediation across human tissue types. However, the presence of complex hidden confounding effects in biological systems can make mediation analyses challenging and prone to confounding bias, particularly when conducted among diverse samples. To address this problem, we propose a new method: Genomic Mediation analysis with Adaptive Confounding adjustment (GMAC). It enables the search of a very large pool of variables, and adaptively selects potential confounding variables for each mediation test. Analyses of simulated data and GTEx data demonstrate that the adaptive selection of confounders by GMAC improves the power and precision of mediation analysis. Application of GMAC to GTEx data provides new insights into the observed patterns of cis-hubs and trans-eQTL regulation across tissue types. PMID:29021290

Identifying cis-mediators for trans-eQTLs across many human tissues using genomic mediation analysis.

PubMed

Yang, Fan; Wang, Jiebiao; Pierce, Brandon L; Chen, Lin S

2017-11-01

The impact of inherited genetic variation on gene expression in humans is well-established. The majority of known expression quantitative trait loci (eQTLs) impact expression of local genes ( cis -eQTLs). More research is needed to identify effects of genetic variation on distant genes ( trans -eQTLs) and understand their biological mechanisms. One common trans -eQTLs mechanism is "mediation" by a local ( cis ) transcript. Thus, mediation analysis can be applied to genome-wide SNP and expression data in order to identify transcripts that are " cis -mediators" of trans -eQTLs, including those " cis -hubs" involved in regulation of many trans -genes. Identifying such mediators helps us understand regulatory networks and suggests biological mechanisms underlying trans -eQTLs, both of which are relevant for understanding susceptibility to complex diseases. The multitissue expression data from the Genotype-Tissue Expression (GTEx) program provides a unique opportunity to study cis -mediation across human tissue types. However, the presence of complex hidden confounding effects in biological systems can make mediation analyses challenging and prone to confounding bias, particularly when conducted among diverse samples. To address this problem, we propose a new method: Genomic Mediation analysis with Adaptive Confounding adjustment (GMAC). It enables the search of a very large pool of variables, and adaptively selects potential confounding variables for each mediation test. Analyses of simulated data and GTEx data demonstrate that the adaptive selection of confounders by GMAC improves the power and precision of mediation analysis. Application of GMAC to GTEx data provides new insights into the observed patterns of cis -hubs and trans -eQTL regulation across tissue types. © 2017 Yang et al.; Published by Cold Spring Harbor Laboratory Press.

Natural Language Processing to Ascertain Two Key Variables from Operative Reports in Ophthalmology

PubMed Central

Liu, Liyan; Shorstein, Neal H.; Amsden, Laura B; Herrinton, Lisa J.

2016-01-01

Purpose Antibiotic prophylaxis is critical to ophthalmology and other surgical specialties. We performed natural language processing (NLP) of 743,838 operative notes recorded for 315,246 surgeries to ascertain two variables needed to study the comparative effectiveness of antibiotic prophylaxis in cataract surgery. The first key variable was an exposure variable, intracameral antibiotic injection. The second was an intraoperative complication, posterior capsular rupture (PCR), that functioned as a potential confounder. To help other researchers use NLP in their settings, we describe our NLP protocol and lessons learned. Methods For each of the two variables, we used SAS Text Miner and other SAS text-processing modules with a training set of 10,000 (1.3%) operative notes to develop a lexicon. The lexica identified misspellings, abbreviations, and negations, and linked words into concepts (e.g., “antibiotic” linked with “injection”). We confirmed the NLP tools by iteratively obtaining random samples of 2,000 (0.3%) notes, with replacement. Results The NLP tools identified approximately 60,000 intracameral antibiotic injections and 3,500 cases of PCR. The positive and negative predictive values for intracameral antibiotic injection exceeded 99%. For the intraoperative complication, they exceeded 94%. Conclusion NLP was a valid and feasible method for obtaining critical variables needed for a research study of surgical safety. These NLP tools were intended for use in the study sample. Use with external datasets or future datasets in our own setting would require further testing. PMID:28052483

Which Propensity Score Method Best Reduces Confounder Imbalance? An Example From a Retrospective Evaluation of a Childhood Obesity Intervention.

PubMed

Schroeder, Krista; Jia, Haomiao; Smaldone, Arlene

Propensity score (PS) methods are increasingly being employed by researchers to reduce bias arising from confounder imbalance when using observational data to examine intervention effects. The purpose of this study was to examine PS theory and methodology and compare application of three PS methods (matching, stratification, weighting) to determine which best improves confounder balance. Baseline characteristics of a sample of 20,518 school-aged children with severe obesity (of whom 1,054 received an obesity intervention) were assessed prior to PS application. Three PS methods were then applied to the data to determine which showed the greatest improvement in confounder balance between the intervention and control group. The effect of each PS method on the outcome variable-body mass index percentile change at one year-was also examined. SAS 9.4 and Comprehensive Meta-analysis statistical software were used for analyses. Prior to PS adjustment, the intervention and control groups differed significantly on seven of 11 potential confounders. PS matching removed all differences. PS stratification and weighting both removed one difference but created two new differences. Sensitivity analyses did not change these results. Body mass index percentile at 1 year decreased in both groups. The size of the decrease was smaller in the intervention group, and the estimate of the decrease varied by PS method. Selection of a PS method should be guided by insight from statistical theory and simulation experiments, in addition to observed improvement in confounder balance. For this data set, PS matching worked best to correct confounder imbalance. Because each method varied in correcting confounder imbalance, we recommend that multiple PS methods be compared for ability to improve confounder balance before implementation in evaluating treatment effects in observational data.

Packet Randomized Experiments for Eliminating Classes of Confounders

PubMed Central

Pavela, Greg; Wiener, Howard; Fontaine, Kevin R.; Fields, David A.; Voss, Jameson D.; Allison, David B.

2014-01-01

Background Although randomization is considered essential for causal inference, it is often not possible to randomize in nutrition and obesity research. To address this, we develop a framework for an experimental design—packet randomized experiments (PREs), which improves causal inferences when randomization on a single treatment variable is not possible. This situation arises when subjects are randomly assigned to a condition (such as a new roommate) which varies in one characteristic of interest (such as weight), but also varies across many others. There has been no general discussion of this experimental design, including its strengths, limitations, and statistical properties. As such, researchers are left to develop and apply PREs on an ad hoc basis, limiting its potential to improve causal inferences among nutrition and obesity researchers. Methods We introduce PREs as an intermediary design between randomized controlled trials and observational studies. We review previous research that used the PRE design and describe its application in obesity-related research, including random roommate assignments, heterochronic parabiosis, and the quasi-random assignment of subjects to geographic areas. We then provide a statistical framework to control for potential packet-level confounders not accounted for by randomization. Results PREs have successfully been used to improve causal estimates of the effect of roommates, altitude, and breastfeeding on weight outcomes. When certain assumptions are met, PREs can asymptotically control for packet-level characteristics. This has the potential to statistically estimate the effect of a single treatment even when randomization to a single treatment did not occur. Conclusions Applying PREs to obesity-related research will improve decisions about clinical, public health, and policy actions insofar as it offers researchers new insight into cause and effect relationships among variables. PMID:25444088

Non-auditory effects of noise in industry. VI. A final field study in industry.

PubMed

van Dijk, F J; Souman, A M; de Vries, F F

1987-01-01

Non-auditory effects of noise were studied among 539 male workers from seven industries. The LAeq, assessed by personal noise dosimetry, has been used to study acute effects. Various indices of total noise exposure, involving level and duration, were developed for long-term effect studies. In the analysis close attention was paid to prevent confounding, e.g. by other adverse working conditions. As expected, hearing loss increased with total noise exposure. Tinnitus was related particularly to hearing loss. Dizziness and hoarseness, however, were not related with noise exposure in this study. Also no correlation could be demonstrated between blood pressure and total noise exposure after correction for age, relative weight and various confounding variables. Use of hearing protection, selection processes and incomplete analysis of interactions between independent variables are suggested for possible explanation. About two-thirds of the workers reported noise annoyance. Various aspects were mentioned, such as irritation, surprise and impairment of communication and perception. Mentally stressful tasks appeared to be the most noise-sensitive. Particularly annoying noise sources, mental work load and time pressure had a relatively large impact on noise annoyance in comparison with the influence of noise level (LAeq) itself. Stress responses were not simply related to the noise exposure level, although consistent positive relations could be demonstrated between symptoms of stress and noise annoyance. Various findings led to the conclusion that noise exposure together with stressful mental activities may lead to disturbed concentration, irritation and annoyance. Experienced stress in turn may render workers more susceptible to noise. To overcome some limitations of this study, cohort studies and studies designed to assess interaction-effects are recommended.

AfroColombian ethnicity, a paradoxical protective factor against Dengue

PubMed Central

Alzate, Alberto; Martínez Romero, Héctor Jairo; Concha-Eastman, Alberto Ignacio

2016-01-01

Introduction: Dengue is a priority public health problem. During epidemics in Cuba and Haiti, ethnic African descendant population had lower risk of dengue, and the ethnic factor was proposed as a protective one. Objective: To determine the relation between the Dengue's cumulative incidence and the Afro-Colombian proportion in communities of Cali, during the epidemic of 2013. Methods: This study was conducted in Cali, Colombia. The design was ecological, using information from the National Census 2005 projected to 2013, from the National Administrative Department of Statistics (DANE), and the National Epidemiological Surveillance System. It was obtained the Pearson´s correlation coefficient between cumulative incidence and the proportion of Afro-Colombian population by communities. Additionally, the cumulative incidences of dengue were evaluated in two zones with different proportion of Afro-Colombian population. The association was also evaluated for aggregation bias, confounding by social variables, and interaction by area of ​​residence. Results: Dengue´s cumulative incidence was significantly lower for Afro-Colombians regardless of the proportion of Afro-Colombian population in the area of residence. The relative risk of dengue between non-Afro-Colombians and Afro-Colombians was 9.4 (95% CI=8.4-10.6) in zones with high proportion of Afro-Colombian population, while the relative risk of dengue was 4.0 (95% CI :3.6 - 4.4) in the zone with lower proportion of Afro-Colombian population. There was no evidence of aggregation bias or confounding in the association by social variables. Conclusions: The Afro-Colombian population had a significantly lower risk of getting dengue and its complications, compared with the non-Afro-Colombian population. The non-Afro-Colombian populations living in areas with a high proportion of Afro-Colombians increase their risk of dengue more than double, suggesting an asymptomatic viremic environment. PMID:27821892

The Association of Albuminuria With Tubular Reabsorption of Uric Acid: Results From a General Population Cohort

PubMed Central

Scheven, Lieneke; Joosten, Michel M.; de Jong, Paul E.; Bakker, Stephan J. L.; Gansevoort, Ron T.

2014-01-01

Background Elevated albuminuria as well as an increased serum uric acid concentration is associated with poor cardiovascular outcome. We questioned whether these 2 variables (albuminuria and serum uric concentration) may be interrelated via tubular uric acid reabsorption. Methods and Results Included were 7688 participants of the PREVEND Study, an observational, general population‐based cohort study. Linear regression analyses were used to test associations of baseline albuminuria with baseline serum uric acid concentration and tubular uric acid reabsorption (calculated as [100−fractional uric acid excretion]%). Cox regression analyses were used to study the association of baseline serum uric acid and albuminuria with incident cardiovascular morbidity and mortality. In cross‐sectional analyses, albuminuria was associated positively with serum uric acid concentration, both crude and after adjustment for potential confounders (both P<0.001). Albuminuria was found to be associated positively with tubular uric acid reabsorption, again both crude and after adjustment for potential confounders (both P<0.001). In longitudinal analyses during a median follow‐up of 10.5 years, 702 cardiovascular events occurred. After adjusting for cardiovascular risk factors, both albuminuria and serum uric acid were associated with incident cardiovascular events (Hazard Ratios 1.09 [1.03 to 1.17], P=0.01 and 1.19 [1.09 to 1.30], P<0.001, respectively). A significant interaction between these variables was present (P<0.001), consistent with high serum uric acid being less predictive for cardiovascular morbidity and mortality in the presence of high albuminuria and vice versa. Conclusions Albuminuria is strongly associated with tubular uric acid reabsorption, and consequently with serum uric acid concentration. This phenomenon may explain in part why albuminuria is associated with cardiovascular outcome. PMID:24772520

Relationship Between Rates of Binocular Visual Field Loss and Vision-Related Quality of Life in Glaucoma

PubMed Central

Lisboa, Renato; Chun, Yeoun Sook; Zangwill, Linda M.; Weinreb, Robert N.; Rosen, Peter N.; Liebmann, Jeffrey M.; Girkin, Christopher A.; Medeiros, Felipe A.

2013-01-01

Objective To evaluate the relationship between binocular rates of visual field change and vision-related quality of life (VRQOL) in glaucoma. Methods The study included 796 eyes of 398 participants that had diagnosed or suspected glaucoma followed for an average of 7.3 ± 2.0 years. Subjects were recruited from the Diagnostic Innovations in Glaucoma Study (DIGS) and the African Descent and Glaucoma Evaluation Study (ADAGES). VRQOL was evaluated using the National Eye Institute Visual Function Questionnaire (NEI VFQ-25) at the last follow-up visit. Integrated binocular visual fields (BVF) were calculated from the monocular fields of each patient. Linear regression of mean deviation (MD) values was used to evaluate rates of visual field change during the follow-up period. Logistic regression models were used to investigate the relationship between abnormal VRQOL and rates of visual field change, while adjusting for potentially confounding socio-economic and demographic variables. Results Thirty-two patients (8.0%) had abnormal VRQOL as determined by the results of the NEI VFQ-25 questionnaire. Subjects with abnormal VRQOL had significantly faster rates of BVF change than those with normal VRQOL (−0.18 db/year vs. −0.06 dB/year, respectively; P < 0.001). Rates of BVF change were significantly associated with abnormality in VRQOL (OR = 1.31 per 0.1dB/year faster; P = 0.038), after adjustment for confounding variables. Conclusions Patients with faster rates of BVF change were at higher risk of reporting abnormal VRQOL. Assessment of rates of BVF change may provide useful information in determining risk of functional impairment in glaucoma. PMID:23450425

Postural control as a function of time-of-day: influence of a prior strenuous running exercise or demanding sustained-attention task

PubMed Central

2013-01-01

Background The current experiment investigated the impact of two potential confounding variables on the postural balance in young participants: the induced-experimental activity prior to the static postural measurements and the well-documented time-of-day effects. We mainly hypothesized that an exhaustive exercise and a high attention-demanding task should result in alterations of postural control. Methods Ten participants performed three experimental sessions (differentiated by the activity – none, cognitive or physical – prior of the assessment of postural stability), separated by one day at least. Each session included postural balance assessments around 8 a.m., 12.00 p.m. and 5 p.m. ± 30 min. The physical and cognitive activities were performed only before the 12 o’clock assessment. The postural tests consisted of four conditions of quiet stance: stance on a firm surface with eyes open; stance on a firm surface with eyes closed; stance on a foam surface with eyes open and stance on a foam surface with eyes closed. Postural performance was assessed by various center of pressure (COP) parameters. Results Overall, the COP findings indicated activity-related postural impairment, with an increase in body sway in the most difficult conditions (with foam surface), especially when postural measurements are recorded just after the running exercise (physical session) or the psychomotor vigilance test (cognitive session). Conclusions Even if no specific influence of time-of-day on static postural control is demonstrated, our results clearly suggest that the activities prior to balance tests could be a potential confounding variable to be taken into account and controlled when assessing clinical postural balance. PMID:23452958

“Skill of Generalized Additive Model to Detect PM2.5 Health ...

EPA Pesticide Factsheets

Summary. Measures of health outcomes are collinear with meteorology and air quality, making analysis of connections between human health and air quality difficult. The purpose of this analysis was to determine time scales and periods shared by the variables of interest (and by implication scales and periods that are not shared). Hospital admissions, meteorology (temperature and relative humidity), and air quality (PM2.5 and daily maximum ozone) for New York City during the period 2000-2006 were decomposed into temporal scales ranging from 2 days to greater than two years using a complex wavelet transform. Health effects were modeled as functions of the wavelet components of meteorology and air quality using the generalized additive model (GAM) framework. This simulation study showed that GAM is extremely successful at extracting and estimating a health effect embedded in a dataset. It also shows that, if the objective in mind is to estimate the health signal but not to fully explain this signal, a simple GAM model with a single confounder (calendar time) whose smooth representation includes a sufficient number of constraints is as good as a more complex model.Introduction. In the context of wavelet regression, confounding occurs when two or more independent variables interact with the dependent variable at the same frequency. Confounding also acts on a variety of time scales, changing the PM2.5 coefficient (magnitude and sign) and its significance ac

Childhood trauma is not a confounder of the overlap between autistic and schizotypal traits: A study in a non-clinical adult sample.

PubMed

Gong, Jing-Bo; Wang, Ya; Lui, Simon S Y; Cheung, Eric F C; Chan, Raymond C K

2017-11-01

Childhood trauma has been shown to be a robust risk factor for mental disorders, and may exacerbate schizotypal traits or contribute to autistic trait severity. However, little is known whether childhood trauma confounds the overlap between schizotypal traits and autistic traits. This study examined whether childhood trauma acts as a confounding variable in the overlap between autistic and schizotypal traits in a large non-clinical adult sample. A total of 2469 participants completed the Autism Spectrum Quotient (AQ), the Schizotypal Personality Questionnaire (SPQ), and the Childhood Trauma Questionnaire-Short Form. Correlation analysis showed that the majority of associations between AQ variables and SPQ variables were significant (p < 0.05). In the multiple regression models predicting scores on the AQ total, scores on the three SPQ subscales were significant predictors(Ps < 0.05). Scores on the Positive schizotypy and Negative schizotypy subscales were significant predictors in the multiple regression model predicting scores on the AQ Social Skill, AQ Attention Switching, AQ Attention to Detail, AQ Communication, and AQ Imagination subscales. The association between autistic and schizotypal traits could not be explained by shared variance in terms of exposure to childhood trauma. The findings point to important overlaps in the conceptualization of ASD and SSD, independent of childhood trauma. Copyright © 2017 Elsevier B.V. All rights reserved.

"Fundamental Causes" of Social Inequalities in Mortality: A Test of the Theory

ERIC Educational Resources Information Center

Phelan, Jo C.; Link, Bruce G.; Diez-Roux, Ana; Kawachi, Ichiro; Levin, Bruce

2004-01-01

Medicine and epidemiology currently dominate the study of the strong association between socioeconomic status and mortality. Socioeconomic status typically is viewed as a causally irrelevant "confounding variable" or as a less critical variable marking only the beginning of a causal chain in which intervening risk factors are given prominence. Yet…

Predicting Teacher Value-Added Results in Non-Tested Subjects Based on Confounding Variables: A Multinomial Logistic Regression

ERIC Educational Resources Information Center

Street, Nathan Lee

2017-01-01

Teacher value-added measures (VAM) are designed to provide information regarding teachers' causal impact on the academic growth of students while controlling for exogenous variables. While some researchers contend VAMs successfully and authentically measure teacher causality on learning, others suggest VAMs cannot adequately control for exogenous…

Are Attractive Men's Faces Masculine or Feminine? The Importance of Controlling Confounds in Face Stimuli

ERIC Educational Resources Information Center

Debruine, Lisa M.; Jones, Benedict C.; Smith, Finlay G.; Little, Anthony C.

2010-01-01

Women's preferences for male masculinity are highly variable. Although many researchers explain this variability as reflecting systematic individual differences in how women resolve the tradeoff between the costs and benefits of choosing a masculine partner, others suggest that methodological differences between studies are responsible. A recent…

Adolescent Substance Use, Sleep, and Academic Achievement: Evidence of Harm Due to Caffeine

ERIC Educational Resources Information Center

James, Jack E.; Kristjansson, Alfgeir Logi; Sigfusdottir, Inga Dora

2011-01-01

Using academic achievement as the key outcome variable, 7377 Icelandic adolescents were surveyed for cigarette smoking, alcohol use, daytime sleepiness, caffeine use, and potential confounders. Structural equation modeling (SEM) was used to examine direct and indirect effects of measured and latent variables in two models: the first with caffeine…

Association between prolonged breast-feeding and early childhood caries: a hierarchical approach.

PubMed

Nunes, Ana Margarida Melo; Alves, Claudia Maria Coelho; Borba de Araújo, Fernando; Ortiz, Tânia Mara Lopes; Ribeiro, Marizélia Rodrigues Costa; Silva, Antônio Augusto Moura da; Ribeiro, Cecília Claudia Costa

2012-12-01

This study was conducted to investigate the association between prolonged breastfeeding and early childhood caries(ECC) with adjustment for important confounders, using hieraschical approach. This retrospective cohort study involved 260 low-income children (18-42 months). The number of decayed teeth was used as a measure of caries. Following a theoretical framework, the hierarchical model was built in a forward fashion, by adding the following levels in succession: level 1: age; level 2: social variables; level 3: health variables; level 4: behavioral variables; level 5: oral hygiene-related variables; level 6: oral hygiene quality measured by visible plaque; and level 7: contamination by mutans streptococci. Sequential forward multiple Poisson regression analysis was employed. Breast-feeding was not a risk factor for ECC after adjustment for some confounders (incidence density ratio, 1.15; 95% confidence interval, 0.84-1.59, P = 0.363). Prolonged breast-feeding was not a risk factor for ECC while age, high sucrose comption between main meals and the quality of oral higiene were associated with disease in children. © 2012 John Wiley & Sons A/S.

Sleep variability and cardiac autonomic modulation in adolescents – Penn State Child Cohort (PSCC) study

PubMed Central

Rodríguez-Colón, Sol M.; He, Fan; Bixler, Edward O.; Fernandez-Mendoza, Julio; Vgontzas, Alexandros N.; Calhoun, Susan; Zheng, Zhi-Jie; Liao, Duanping

2015-01-01

Objective To investigate the effects of objectively measured habitual sleep patterns on cardiac autonomic modulation (CAM) in a population-based sample of adolescents. Methods We used data from 421 adolescents who completed the follow-up examination in the Penn State Children Cohort study. CAM was assessed by heart rate (HR) variability (HRV) analysis of beat-to-beat normal R-R intervals from a 39-h electrocardiogram, on a 30-min basis. The HRV indices included frequency domain (HF, LF, and LF/HF ratio), and time domain (SDNN, RMSSD, and heart rate or HR) variables. Actigraphy was used for seven consecutive nights to estimate nightly sleep duration and time in bed. The seven-night mean (SD) of sleep duration and sleep efficiency were used to represent sleep duration, duration variability, sleep efficiency, and efficiency variability, respectively. HF and LF were log-transformed for statistical analysis. Linear mixed-effect models were used to analyze the association between sleep patterns and CAM. Results After adjusting for major confounders, increased sleep duration variability and efficiency variability were significantly associated with lower HRV and higher HR during the 39-h, as well as separated by daytime and nighttime. For instance, a 1-h increase in sleep duration variability is associated with −0.14(0.04), −0.12(0.06), and −0.16(0.05) ms2 decrease in total, daytime, and nighttime HF, respectively. No associations were found between sleep duration, or sleep efficiency and HRV. Conclusion Higher habitual sleep duration variability and efficiency variability are associated with lower HRV and higher HR, suggesting that an irregular sleep pattern has an adverse impact on CAM, even in healthy adolescents. PMID:25555635

Using instrumental variables to disentangle treatment and placebo effects in blinded and unblinded randomized clinical trials influenced by unmeasured confounders

NASA Astrophysics Data System (ADS)

Chaibub Neto, Elias

2016-11-01

Clinical trials traditionally employ blinding as a design mechanism to reduce the influence of placebo effects. In practice, however, it can be difficult or impossible to blind study participants and unblinded trials are common in medical research. Here we show how instrumental variables can be used to quantify and disentangle treatment and placebo effects in randomized clinical trials comparing control and active treatments in the presence of confounders. The key idea is to use randomization to separately manipulate treatment assignment and psychological encouragement conversations/interactions that increase the participants’ desire for improved symptoms. The proposed approach is able to improve the estimation of treatment effects in blinded studies and, most importantly, opens the doors to account for placebo effects in unblinded trials.

Perceived Discrimination among African American Adolescents and Allostatic Load: A Longitudinal Analysis with Buffering Effects

PubMed Central

Brody, Gene H.; Lei, Man-Kit; Chae, David H.; Yu, Tianyi; Kogan, Steven M.; Beach, Steven R. H.

2013-01-01

This study was designed to examine the prospective relations of perceived racial discrimination with allostatic load (AL), along with a possible buffer of the association. A sample of 331 African Americans in the rural South provided assessments of perceived discrimination from ages 16 to 18 years. When youths were 18, caregivers reported parental emotional support, and youths assessed peer emotional support. AL and potential confounder variables were assessed when youths were 20. Latent Growth Mixture Modeling identified two perceived discrimination classes: high and stable and low and increasing. Adolescents in the high and stable class evinced heightened AL even with confounder variables controlled. The racial discrimination to AL link was not significant for young adults who received high emotional support. PMID:24673162

The role of sex and body weight on the metabolic effects of high-fat diet in C57BL/6N mice.

PubMed

Ingvorsen, C; Karp, N A; Lelliott, C J

2017-04-10

Metabolic disorders are commonly investigated using knockout and transgenic mouse models on the C57BL/6N genetic background due to its genetic susceptibility to the deleterious metabolic effects of high-fat diet (HFD). There is growing awareness of the need to consider sex in disease progression, but limited attention has been paid to sexual dimorphism in mouse models and its impact in metabolic phenotypes. We assessed the effect of HFD and the impact of sex on metabolic variables in this strain. We generated a reference data set encompassing glucose tolerance, body composition and plasma chemistry data from 586 C57BL/6N mice fed a standard chow and 733 fed a HFD collected as part of a high-throughput phenotyping pipeline. Linear mixed model regression analysis was used in a dual analysis to assess the effect of HFD as an absolute change in phenotype, but also as a relative change accounting for the potential confounding effect of body weight. HFD had a significant impact on all variables tested with an average absolute effect size of 29%. For the majority of variables (78%), the treatment effect was modified by sex and this was dominated by male-specific or a male stronger effect. On average, there was a 13.2% difference in the effect size between the male and female mice for sexually dimorphic variables. HFD led to a significant body weight phenotype (24% increase), which acts as a confounding effect on the other analysed variables. For 79% of the variables, body weight was found to be a significant source of variation, but even after accounting for this confounding effect, similar HFD-induced phenotypic changes were found to when not accounting for weight. HFD and sex are powerful modifiers of metabolic parameters in C57BL/6N mice. We also demonstrate the value of considering body size as a covariate to obtain a richer understanding of metabolic phenotypes.

Using Animal Models to Determine the Role of Gustatory Neural Input in the Control of Ingestive Behavior and the Maintenance of Body Weight

PubMed Central

Ciullo, Dana L.

2015-01-01

Introduction Decades of research have suggested that nutritional intake contributes to the development of human disease, mainly by influencing the development of obesity and obesity-related conditions. A relatively large body of research indicates that functional variation in human taste perception can influence nutritional intake as well as body mass accumulation. However, there are a considerable number of studies that suggest that no link between these variables actually exists. These discrepancies in the literature likely result from the confounding influence of a variety of other, uncontrolled, factors that can influence ingestive behavior. Strategy In this review, the use of controlled animal experimentation to alleviate at least some of these issues related to the lack of control of experimental variables is discussed. Specific examples of the use of some of these techniques are examined. Discussion and conclusions The review will close with some specific suggestions aimed at strengthening the link between gustatory neural input and its putative influence on ingestive behaviors and the maintenance of body weight. PMID:26557212

Preanalytical Confounding Factors in the Analysis of Cerebrospinal Fluid Biomarkers for Alzheimer’s Disease: The Issue of Diurnal Variation

PubMed Central

Cicognola, Claudia; Chiasserini, Davide; Parnetti, Lucilla

2015-01-01

Given the growing use of cerebrospinal fluid (CSF) beta-amyloid (Aβ) and tau as biomarkers for early diagnosis of Alzheimer’s disease (AD), it is essential that the diagnostic procedures are standardized and the results comparable across different laboratories. Preanalytical factors are reported to be the cause of at least 50% of the total variability. Among them, diurnal variability is a key issue and may have an impact on the comparability of the values obtained. The available studies on this issue are not conclusive so far. Fluctuations of CSF biomarkers in young healthy volunteers have been previously reported, while subsequent studies have not confirmed those observations in older subjects, the ones most likely to receive this test. The observed differences in circadian rhythms need to be further assessed not only in classical CSF biomarkers but also in novel forthcoming biomarkers. In this review, the existing data on the issue of diurnal variations of CSF classical biomarkers for AD will be analyzed, also evaluating the available data on new possible biomarkers. PMID:26175714

Confounding factors in determining causal soil moisture-precipitation feedback

NASA Astrophysics Data System (ADS)

Tuttle, Samuel E.; Salvucci, Guido D.

2017-07-01

Identification of causal links in the land-atmosphere system is important for construction and testing of land surface and general circulation models. However, the land and atmosphere are highly coupled and linked by a vast number of complex, interdependent processes. Statistical methods, such as Granger causality, can help to identify feedbacks from observational data, independent of the different parameterizations of physical processes and spatiotemporal resolution effects that influence feedbacks in models. However, statistical causal identification methods can easily be misapplied, leading to erroneous conclusions about feedback strength and sign. Here, we discuss three factors that must be accounted for in determination of causal soil moisture-precipitation feedback in observations and model output: seasonal and interannual variability, precipitation persistence, and endogeneity. The effect of neglecting these factors is demonstrated in simulated and observational data. The results show that long-timescale variability and precipitation persistence can have a substantial effect on detected soil moisture-precipitation feedback strength, while endogeneity has a smaller effect that is often masked by measurement error and thus is more likely to be an issue when analyzing model data or highly accurate observational data.

Identification of confounders in the assessment of the relationship between lead exposure and child development.

PubMed

Tong, I S; Lu, Y

2001-01-01

To explore the best approach to identify and adjust for confounders in epidemiologic practice. In the Port Pirie cohort study, the selection of covariates was based on both a priori and an empirical consideration. In an assessment of the relationship between exposure to environmental lead and child development, change-in-estimate (CE) and significance testing (ST) criteria were compared in identifying potential confounders. The Pearson correlation coefficients were used to evaluate the potential for collinearity between pairs of major quantitative covariates. In multivariate analyses, the effects of confounding factors were assessed with multiple linear regression models. The nature and number of covariates selected varied with different confounder selection criteria and different cutoffs. Four covariates (i.e., quality of home environment, socioeconomic status (SES), maternal intelligence, and parental smoking behaviour) met the conventional CE criterion (> or =10%), whereas 14 variables met the ST criterion (p < or = 0.25). However, the magnitude of the relationship between blood lead concentration and children's IQ differed slightly after adjustment for confounding, using either the CE (partial regression coefficient: -4.4; 95% confidence interval (CI): -0.5 to -8.3) or ST criterion (-4.3; 95% CI: -0.2 to -8.4). Identification and selection of confounding factors need to be viewed cautiously in epidemiologic studies. Either the CE (e.g., > or = 10%) or ST (e.g., p < or = 0.25) criterion may be implemented in identification of a potential confounder if a study sample is sufficiently large, and both the methods are subject to arbitrariness of selecting a cut-off point. In this study, the CE criterion (i.e., > or = 10%) appears to be more stringent than the ST method (i.e., p < or = 0.25) in the identification of confounders. However, the ST rule cannot be used to determine the trueness of confounding because it cannot reflect the causal relationship between the confounder and outcome. This study shows the complexities one can expect to encounter in the identification of and adjustment for confounders.

Validation sampling can reduce bias in healthcare database studies: an illustration using influenza vaccination effectiveness

PubMed Central

Nelson, Jennifer C.; Marsh, Tracey; Lumley, Thomas; Larson, Eric B.; Jackson, Lisa A.; Jackson, Michael

2014-01-01

Objective Estimates of treatment effectiveness in epidemiologic studies using large observational health care databases may be biased due to inaccurate or incomplete information on important confounders. Study methods that collect and incorporate more comprehensive confounder data on a validation cohort may reduce confounding bias. Study Design and Setting We applied two such methods, imputation and reweighting, to Group Health administrative data (full sample) supplemented by more detailed confounder data from the Adult Changes in Thought study (validation sample). We used influenza vaccination effectiveness (with an unexposed comparator group) as an example and evaluated each method’s ability to reduce bias using the control time period prior to influenza circulation. Results Both methods reduced, but did not completely eliminate, the bias compared with traditional effectiveness estimates that do not utilize the validation sample confounders. Conclusion Although these results support the use of validation sampling methods to improve the accuracy of comparative effectiveness findings from healthcare database studies, they also illustrate that the success of such methods depends on many factors, including the ability to measure important confounders in a representative and large enough validation sample, the comparability of the full sample and validation sample, and the accuracy with which data can be imputed or reweighted using the additional validation sample information. PMID:23849144

Assessing the determinants of evolutionary rates in the presence of noise.

PubMed

Plotkin, Joshua B; Fraser, Hunter B

2007-05-01

Although protein sequences are known to evolve at vastly different rates, little is known about what determines their rate of evolution. However, a recent study using principal component regression (PCR) has concluded that evolutionary rates in yeast are primarily governed by a single determinant related to translation frequency. Here, we demonstrate that noise in biological data can confound PCRs, leading to spurious conclusions. When equalizing noise levels across 7 predictor variables used in previous studies, we find no evidence that protein evolution is dominated by a single determinant. Our results indicate that a variety of factors--including expression level, gene dispensability, and protein-protein interactions--may independently affect evolutionary rates in yeast. More accurate measurements or more sophisticated statistical techniques will be required to determine which one, if any, of these factors dominates protein evolution.

Longitudinal associations between sleep duration and subsequent weight gain: A systematic review

PubMed Central

Magee, Lorrie

2011-01-01

Objective To systematically examine the relationship between sleep duration and subsequent weight gain in observational longitudinal human studies Methods Systematic review of twenty longitudinal studies published from 2004-October 31, 2010 Results While adult studies (n=13) reported inconsistent results on the relationship between sleep duration and subsequent weight gain, studies with children (n=7) more consistently reported a positive relationship between short sleep duration and weight gain. Conclusion While shorter sleep duration consistently predicts subsequent weight gain in children, the relationship is not clear in adults. We discuss possible limitations of the current studies: 1.) the diminishing association between short sleep duration on weight gain over time after transition to short sleep, 2.) lack of inclusion of appropriate confounding, mediating, and moderating variables (i.e. sleep complaints and sedentary behavior), and 3.) measurement issues. PMID:21784678

Incidence of workers compensation indemnity claims across socio-demographic and job characteristics.

PubMed

Du, Juan; Leigh, J Paul

2011-10-01

We hypothesized that low socioeconomic status, employer-provided health insurance, low wages, and overtime were predictors of reporting workers compensation indemnity claims. We also tested for gender and race disparities. Responses from 17,190 (person-years) Americans participating in the Panel Study of Income Dynamics, 1997-2005, were analyzed with logistic regressions. The dependent variable indicated whether the subject collected benefits from a claim. Odds ratios for men and African-Americans were relatively large and strongly significant predictors of claims; significance for Hispanics was moderate and confounded by education. Odds ratios for variables measuring education were the largest for all statistically significant covariates. Neither low wages nor employer-provided health insurance was a consistent predictor. Due to confounding from the "not salaried" variable, overtime was not a consistently significant predictor. Few studies use nationally representative longitudinal data to consider which demographic and job characteristics predict reporting workers compensation indemnity cases. This study did and tested some common hypotheses about predictors. Copyright © 2011 Wiley-Liss, Inc.

Doubly robust matching estimators for high dimensional confounding adjustment.

PubMed

Antonelli, Joseph; Cefalu, Matthew; Palmer, Nathan; Agniel, Denis

2018-05-11

Valid estimation of treatment effects from observational data requires proper control of confounding. If the number of covariates is large relative to the number of observations, then controlling for all available covariates is infeasible. In cases where a sparsity condition holds, variable selection or penalization can reduce the dimension of the covariate space in a manner that allows for valid estimation of treatment effects. In this article, we propose matching on both the estimated propensity score and the estimated prognostic scores when the number of covariates is large relative to the number of observations. We derive asymptotic results for the matching estimator and show that it is doubly robust in the sense that only one of the two score models need be correct to obtain a consistent estimator. We show via simulation its effectiveness in controlling for confounding and highlight its potential to address nonlinear confounding. Finally, we apply the proposed procedure to analyze the effect of gender on prescription opioid use using insurance claims data. © 2018, The International Biometric Society.

Effect decomposition in the presence of an exposure-induced mediator-outcome confounder

PubMed Central

VanderWeele, Tyler J.; Vansteelandt, Stijn; Robins, James M.

2014-01-01

Methods from causal mediation analysis have generalized the traditional approach to direct and indirect effects in the epidemiologic and social science literature by allowing for interaction and non-linearities. However, the methods from the causal inference literature have themselves been subject to a major limitation in that the so-called natural direct and indirect effects that are employed are not identified from data whenever there is a variable that is affected by the exposure, which also confounds the relationship between the mediator and the outcome. In this paper we describe three alternative approaches to effect decomposition that give quantities that can be interpreted as direct and indirect effects, and that can be identified from data even in the presence of an exposure-induced mediator-outcome confounder. We describe a simple weighting-based estimation method for each of these three approaches, illustrated with data from perinatal epidemiology. The methods described here can shed insight into pathways and questions of mediation even when an exposure-induced mediator-outcome confounder is present. PMID:24487213

CADDIS Volume 4. Data Analysis: Basic Principles & Issues

EPA Pesticide Factsheets

Use of inferential statistics in causal analysis, introduction to data independence and autocorrelation, methods to identifying and control for confounding variables, references for the Basic Principles section of Data Analysis.

Mendelian Randomization.

PubMed

Grover, Sandeep; Del Greco M, Fabiola; Stein, Catherine M; Ziegler, Andreas

2017-01-01

Confounding and reverse causality have prevented us from drawing meaningful clinical interpretation even in well-powered observational studies. Confounding may be attributed to our inability to randomize the exposure variable in observational studies. Mendelian randomization (MR) is one approach to overcome confounding. It utilizes one or more genetic polymorphisms as a proxy for the exposure variable of interest. Polymorphisms are randomly distributed in a population, they are static throughout an individual's lifetime, and may thus help in inferring directionality in exposure-outcome associations. Genome-wide association studies (GWAS) or meta-analyses of GWAS are characterized by large sample sizes and the availability of many single nucleotide polymorphisms (SNPs), making GWAS-based MR an attractive approach. GWAS-based MR comes with specific challenges, including multiple causality. Despite shortcomings, it still remains one of the most powerful techniques for inferring causality.With MR still an evolving concept with complex statistical challenges, the literature is relatively scarce in terms of providing working examples incorporating real datasets. In this chapter, we provide a step-by-step guide for causal inference based on the principles of MR with a real dataset using both individual and summary data from unrelated individuals. We suggest best possible practices and give recommendations based on the current literature.

Clustering Words to Match Conditions: An Algorithm for Stimuli Selection in Factorial Designs

ERIC Educational Resources Information Center

Guasch, Marc; Haro, Juan; Boada, Roger

2017-01-01

With the increasing refinement of language processing models and the new discoveries about which variables can modulate these processes, stimuli selection for experiments with a factorial design is becoming a tough task. Selecting sets of words that differ in one variable, while matching these same words into dozens of other confounding variables…

A review of covariate selection for non-experimental comparative effectiveness research.

PubMed

Sauer, Brian C; Brookhart, M Alan; Roy, Jason; VanderWeele, Tyler

2013-11-01

This paper addresses strategies for selecting variables for adjustment in non-experimental comparative effectiveness research and uses causal graphs to illustrate the causal network that relates treatment to outcome. Variables in the causal network take on multiple structural forms. Adjustment for a common cause pathway between treatment and outcome can remove confounding, whereas adjustment for other structural types may increase bias. For this reason, variable selection would ideally be based on an understanding of the causal network; however, the true causal network is rarely known. Therefore, we describe more practical variable selection approaches based on background knowledge when the causal structure is only partially known. These approaches include adjustment for all observed pretreatment variables thought to have some connection to the outcome, all known risk factors for the outcome, and all direct causes of the treatment or the outcome. Empirical approaches, such as forward and backward selection and automatic high-dimensional proxy adjustment, are also discussed. As there is a continuum between knowing and not knowing the causal, structural relations of variables, we recommend addressing variable selection in a practical way that involves a combination of background knowledge and empirical selection and that uses high-dimensional approaches. This empirical approach can be used to select from a set of a priori variables based on the researcher's knowledge to be included in the final analysis or to identify additional variables for consideration. This more limited use of empirically derived variables may reduce confounding while simultaneously reducing the risk of including variables that may increase bias. Copyright © 2013 John Wiley & Sons, Ltd.

A Review of Covariate Selection for Nonexperimental Comparative Effectiveness Research

PubMed Central

Sauer, Brian C.; Brookhart, Alan; Roy, Jason; Vanderweele, Tyler

2014-01-01

This paper addresses strategies for selecting variables for adjustment in non-experimental comparative effectiveness research (CER), and uses causal graphs to illustrate the causal network that relates treatment to outcome. Variables in the causal network take on multiple structural forms. Adjustment for on a common cause pathway between treatment and outcome can remove confounding, while adjustment for other structural types may increase bias. For this reason variable selection would ideally be based on an understanding of the causal network; however, the true causal network is rarely know. Therefore, we describe more practical variable selection approaches based on background knowledge when the causal structure is only partially known. These approaches include adjustment for all observed pretreatment variables thought to have some connection to the outcome, all known risk factors for the outcome, and all direct causes of the treatment or the outcome. Empirical approaches, such as forward and backward selection and automatic high-dimensional proxy adjustment, are also discussed. As there is a continuum between knowing and not knowing the causal, structural relations of variables, we recommend addressing variable selection in a practical way that involves a combination of background knowledge and empirical selection and that uses the high-dimensional approaches. This empirical approach can be used to select from a set of a priori variables based on the researcher’s knowledge to be included in the final analysis or to identify additional variables for consideration. This more limited use of empirically-derived variables may reduce confounding while simultaneously reducing the risk of including variables that may increase bias. PMID:24006330

An assessment of the possible extent of confounding in epidemiological studies of lung cancer risk among roofers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mundt, D.J.; van Wijngaarden, E.; Mundt, K.A.

2007-07-01

We evaluated the likelihood and extent to which the observed increased risk of lung cancer may be due to confounding (a mixing of effects of multiple exposures) by co-exposure to other potential carcinogens present in roofing or to lifestyle variables. We conducted a review of the epidemiological and industrial hygiene literature of asphalt-exposed workers. Peer-reviewed epidemiological studies of asphalt fumes, related occupational exposures, and confounding factors were identified from MEDLINE (1966 early 2004). Industrial hygiene studies of asphalt workers were identified through MEDLINE, publicly available government documents, and asphalt industry documents. Using well established statistical methods, we quantified the extentmore » to which lung cancer relative risk estimates among roofers reflect confounding from other exposures, using different prevalence and risk scenarios. The relative risk of lung cancer varied from 1.2 to 5.0 in 13 epidemiological studies of roofers; most studies reported a relative risk between 1.2 and 1.4. Smoking, asbestos and coal tar were the most likely confounders, but the prevalence of these factors varied over time. The results of the study indicate that much of the observed risk reported in epidemiological studies of cancer among roofers is well within the range of what may have resulted from confounding by reasonable and expected levels of smoking, asbestos or coal tar. This may be particularly true for those studies that did not adjust for these confounders and where the exposure was defined as employment in the roofing industry. In addition to poorly defined asphalt exposure, uncontrolled confounding cannot reliably be ruled out in studies of lung cancer among asphalt-exposed roofers. Therefore, it is not possible to conclude whether roofers are at increased risk of lung cancer due to asphalt exposure.« less

External adjustment sensitivity analysis for unmeasured confounding: an application to coronary stent outcomes, Pennsylvania 2004-2008.

PubMed

Huesch, Marco D

2013-06-01

Assessing the real-world comparative effectiveness of common interventions is challenged by unmeasured confounding. To determine whether the mortality benefit shown for drug-eluting stents (DES) over bare metal stents (BMS) in observational studies persists after controls for/tests for confounding. Retrospective observational study involving 38,019 patients, 65 years or older admitted for an index percutaneous coronary intervention receiving DES or BMS in Pennsylvania in 2004-2005 followed up for death through 3 years. Analysis was at the patient level. Mortality was analyzed with Cox proportional hazards models allowing for stratification by disease severity or DES use propensity, accounting for clustering of patients. Instrumental variables analysis used lagged physician stent usage to proxy for the focal stent type decision. A method originating in work by Cornfield and others in 1954 and popularized by Greenland in 1996 was used to assess robustness to confounding. DES was associated with a significantly lower adjusted risk of death at 3 years in Cox and in instrumented analyses. An implausibly strong hypothetical unobserved confounder would be required to fully explain these results. Confounding by indication can bias observational studies. No strong evidence of such selection biases was found in the reduced risk of death among elderly patients receiving DES instead of BMS in a Pennsylvanian state-wide population. © Health Research and Educational Trust.

Why Do Thin People Have Elevated All-Cause Mortality? Evidence on Confounding and Reverse Causality in the Association of Adiposity and COPD from the British Women’s Heart and Health Study

PubMed Central

Dale, Caroline; Nüesch, Eveline; Prieto-Merino, David; Choi, Minkyoung; Amuzu, Antoinette; Ebrahim, Shah; Casas, Juan P.; Davey-Smith, George

2015-01-01

Low adiposity has been linked to elevated mortality from several causes including respiratory disease. However, this could arise from confounding or reverse causality. We explore the association between two measures of adiposity (BMI and WHR) with COPD in the British Women’s Heart and Health Study including a detailed assessment of the potential for confounding and reverse causality for each adiposity measure. Low BMI was found to be associated with increased COPD risk while low WHR was not (OR = 2.2; 95% CI 1.3 – 3.1 versus OR = 1.2; 95% CI 0.7 – 1.6). Potential confounding variables (e.g. smoking) and markers of ill-health (e.g. unintentional weight loss) were found to be higher in low BMI but not in low WHR. Women with low BMI have a detrimental profile across a broad range of health markers compared to women with low WHR, and women with low WHR do not appear to have an elevated COPD risk, lending support to the hypothesis that WHR is a less confounded measure of adiposity than BMI. Low adiposity does not in itself appear to increase the risk of respiratory disease, and the apparent adverse consequences of low BMI may be due to reverse causation and confounding. PMID:25884834

Impact sports and bone fractures among adolescents.

PubMed

Lynch, Kyle R; Kemper, Han C G; Turi-Lynch, Bruna; Agostinete, Ricardo R; Ito, Igor H; Luiz-De-Marco, Rafael; Rodrigues-Junior, Mario A; Fernandes, Rômulo A

2017-12-01

The objective of the present study was to investigate the effects of different sports on stress fractures among adolescents during a 9-month follow-up period. The sample was composed of 184 adolescents divided into three groups (impact sports [n = 102]; swimming [n = 35]; non-sports [n = 47]). The occurrence of stress fracture was reported by participants and coaches. As potential confounders we considered age, sex, resistance training, body composition variables and age at peak of height velocity. There were 13 adolescents who reported fractures during the 9-month period. Bone mineral density values were higher in adolescents engaged in impact sports (P-value = 0.002). Independently of confounders, the risk of stress fracture was lower in adolescents engaged in impact sports than in non-active adolescents (hazard ratio [HR] = 0.23 [95% confidence interval (CI) = 0.05 to 0.98]), while swimming practice was not associated to lower risk of fracture (HR = 0.49 [95% CI = 0.09 to 2.55]). In conclusion, the findings from this study indicate the importance of sports participation among adolescents in the reduction of stress fracture risk, especially with impact sports. More importantly, these results could be relevant for recognising adolescents in danger of not reaching their potential for peak bone mass and later an increased risk of fractures.

Rumination, anxiety, depressive symptoms and subsequent depression in adolescents at risk for psychopathology: a longitudinal cohort study

PubMed Central

2013-01-01

Background A ruminative style of responding to low mood is associated with subsequent high depressive symptoms and depressive disorder in children, adolescents and adults. Scores on self-report rumination scales correlate strongly with scores on anxiety and depression symptom scales. This may confound any associations between rumination and subsequent depression. Methods Our sample comprised 658 healthy adolescents at elevated risk for psychopathology. This study applied ordinal item (non-linear) factor analysis to pooled items from three self-report questionnaires to explore whether there were separate, but correlated, constructs of rumination, depression and anxiety. It then tested whether rumination independently predicted depressive disorder and depressive symptoms over the subsequent 12 months, after adjusting for confounding variables. Results We identified a single rumination factor, which was correlated with factors representing cognitive symptoms of depression, somatic symptoms of depression and anxiety symptoms; and one factor representing adaptive responses to low mood. Elevated rumination scores predicted onset of depressive disorders over the subsequent year (p = 0.035), and levels of depressive symptoms 12 months later (p < 0.0005), after adjustment for prior levels of depressive and anxiety symptoms. Conclusion High rumination predicts onset of depressive disorder in healthy adolescents. Therapy that reduces rumination and increases distraction/problem-solving may reduce onset and relapse rates of depression. PMID:24103296

Labor patterns in twin gestations

PubMed Central

Leftwich, Heidi K.; Zaki, Mary N.; Wilkins, Isabelle; Hibbard, Judith U.

2014-01-01

Objective To compare labor progression in twin vs singleton gestations. Study Design Retrospective review of electronic database created by Consortium on Safe Labor, reflecting labor and delivery information from 12 clinical centers 2002-2008. Women with twin gestations, cephalic presentation of presenting twin, gestational age ≥34 weeks, with ≥2 cervical examinations were included. Exclusion criteria were fetal anomalies or demise. Singleton controls were selected by the same criteria. Categorical variables were analyzed by χ2; continuous by Student t test. Interval censored regression was used to determine distribution for time of cervical dilation in centimeters, or “traverse times,” and controlled for confounding factors. Repeated-measures analysis constructed mean labor curves by parity and number of fetuses. Results A total of 891 twin gestations were compared with 100,513 singleton controls. Twin gestations were more often older, white or African American, earlier gestational age, increased prepregnancy body mass index, and with lower birthweight. There was no difference in number of prior cesarean deliveries, induction, or augmentation, or epidural use. Median traverse times increased at every centimeter interval in nulliparous twins, in both unadjusted and adjusted analysis (P < .01). A similar pattern was noted for multiparas in both analyses. Labor curves demonstrated a delayed inflection point in the labor pattern for nulliparous and multiparous twin gestations. Conclusion Both nulliparous and multiparous women have slower progression of active phase labor with twins even when controlling for confounding factors. PMID:23871795

Living in stressful neighbourhoods during pregnancy: an observational study of crime rates and birth outcomes

PubMed Central

Clemens, Tom

2017-01-01

Abstract Background: Patterns of adverse birth outcomes vary spatially and there is evidence that this may relate to features of the physical environment such as air pollution. However, other social characteristics of the environment such as levels of crime are relatively understudied. This study examines the association between crime rates and birth weight and prematurity. Methods: Maternity inpatient data recorded at birth, including residential postcode, was linked to a representative 5% sample of Scottish Census data and small area crime rates from Scottish Police forces. Coefficients associated with crime were reported from crude and confounder adjusted models predicting low birth weight (< 2500 g), mean birthweight, small for gestational age and prematurity for all singleton live births. Results: Total crime rates were associated with strong and significant reductions in mean birth weight and increases in the risks of both a small for gestational age baby and premature birth. These effects, with the exception of prematurity, were robust to adjustment for individual characteristics including smoking, ethnicity and other socio-economic variables as well as area based confounders including air pollution. Mean birth weight was robust to additional adjustment for neighbourhood income deprivation. Conclusion: The level of crime in a mother’s area of residence, which may be a proxy for the degree of threat felt and therefore stress experienced, appears to be an important determinant of the risk of adverse birth outcomes. PMID:27578830

Uncertainty quantification of wall shear stress in intracranial aneurysms using a data-driven statistical model of systemic blood flow variability.

PubMed

Sarrami-Foroushani, Ali; Lassila, Toni; Gooya, Ali; Geers, Arjan J; Frangi, Alejandro F

2016-12-08

Adverse wall shear stress (WSS) patterns are known to play a key role in the localisation, formation, and progression of intracranial aneurysms (IAs). Complex region-specific and time-varying aneurysmal WSS patterns depend both on vascular morphology as well as on variable systemic flow conditions. Computational fluid dynamics (CFD) has been proposed for characterising WSS patterns in IAs; however, CFD simulations often rely on deterministic boundary conditions that are not representative of the actual variations in blood flow. We develop a data-driven statistical model of internal carotid artery (ICA) flow, which is used to generate a virtual population of waveforms used as inlet boundary conditions in CFD simulations. This allows the statistics of the resulting aneurysmal WSS distributions to be computed. It is observed that ICA waveform variations have limited influence on the time-averaged WSS (TAWSS) on the IA surface. In contrast, in regions where the flow is locally highly multidirectional, WSS directionality and harmonic content are strongly affected by the ICA flow waveform. As a consequence, we argue that the effect of blood flow variability should be explicitly considered in CFD-based IA rupture assessment to prevent confounding the conclusions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Sports practice is related to parasympathetic activity in adolescents

PubMed Central

Cayres, Suziane Ungari; Vanderlei, Luiz Carlos Marques; Rodrigues, Aristides Machado; Coelho e Silva, Manuel João; Codogno, Jamile Sanches; Barbosa, Maurício Fregonesi; Fernandes, Rômulo Araújo

2015-01-01

OBJECTIVE: To analyze the relationship among sports practice, physical education class, habitual physical activity and cardiovascular risk in adolescents. METHODS: Cross-sectional study with 120 schoolchildren (mean: 11.7±0.7 years old), with no regular use of medicines. Sports practice and physical education classes were assessed through face-to-face interview, while habitual physical activity was assessed by pedometers. Bodyweight, height and height-cephalic trunk were used to estimate maturation. The following variables were measured: body fatness, blood pressure, resting heart rate, blood flow velocity, intima-media thickness (carotid and femoral) and heart rate variability (mean between consecutive heartbeats and statistical index in the time domain that show the autonomic parasympathetic nervous system activity root-mean by the square of differences between adjacent normal R-R intervals in a time interval). Statistical treatment used Spearman correlation adjusted by sex, ethnicity, age, body fatness and maturation. RESULTS: Independently of potential confounders, sports practice was positively related to autonomic parasympathetic nervous system activity (β=0.039 [0.01; 0.76]). On the other hand, the relationship between sport practice and mean between consecutive heartbeats (β=0,031 [-0.01; 0.07]) was significantly mediated by biological maturation. CONCLUSIONS: Sport practice was related to higher heart rate variability at rest. PMID:25887927

Task-switching cost and repetition priming: two overlooked confounds in the first-set procedure of the Sternberg paradigm and how they affect memory set-size effects.

PubMed

Jou, Jerwen

2014-10-01

Subjects performed Sternberg-type memory recognition tasks (Sternberg paradigm) in four experiments. Category-instance names were used as learning and testing materials. Sternberg's original experiments demonstrated a linear relation between reaction time (RT) and memory-set size (MSS). A few later studies found no relation, and other studies found a nonlinear relation (logarithmic) between the two variables. These deviations were used as evidence undermining Sternberg's serial scan theory. This study identified two confounding variables in the fixed-set procedure of the paradigm (where multiple probes are presented at test for a learned memory set) that could generate a MSS RT function that was either flat or logarithmic rather than linearly increasing. These two confounding variables were task-switching cost and repetition priming. The former factor worked against smaller memory sets and in favour of larger sets whereas the latter factor worked in the opposite way. Results demonstrated that a null or a logarithmic RT-to-MSS relation could be the artefact of the combined effects of these two variables. The Sternberg paradigm has been used widely in memory research, and a thorough understanding of the subtle methodological pitfalls is crucial. It is suggested that a varied-set procedure (where only one probe is presented at test for a learned memory set) is a more contamination-free procedure for measuring the MSS effects, and that if a fixed-set procedure is used, it is worthwhile examining the RT function of the very first trials across the MSSs, which are presumably relatively free of contamination by the subsequent trials.

Improving observational study estimates of treatment effects using joint modeling of selection effects and outcomes: the case of AAA repair.

PubMed

O'Malley, A James; Cotterill, Philip; Schermerhorn, Marc L; Landon, Bruce E

2011-12-01

When 2 treatment approaches are available, there are likely to be unmeasured confounders that influence choice of procedure, which complicates estimation of the causal effect of treatment on outcomes using observational data. To estimate the effect of endovascular (endo) versus open surgical (open) repair, including possible modification by institutional volume, on survival after treatment for abdominal aortic aneurysm, accounting for observed and unobserved confounding variables. Observational study of data from the Medicare program using a joint model of treatment selection and survival given treatment to estimate the effects of type of surgery and institutional volume on survival. We studied 61,414 eligible repairs of intact abdominal aortic aneurysms during 2001 to 2004. The outcome, perioperative death, is defined as in-hospital death or death within 30 days of operation. The key predictors are use of endo, transformed endo and open volume, and endo-volume interactions. There is strong evidence of nonrandom selection of treatment with potential confounding variables including institutional volume and procedure date, variables not typically adjusted for in clinical trials. The best fitting model included heterogeneous transformations of endo volume for endo cases and open volume for open cases as predictors. Consistent with our hypothesis, accounting for unmeasured selection reduced the mortality benefit of endo. The effect of endo versus open surgery varies nonlinearly with endo and open volume. Accounting for institutional experience and unmeasured selection enables better decision-making by physicians making treatment referrals, investigators evaluating treatments, and policy makers.

Risk factors for recurrent gastroesophageal reflux disease after fundoplication in pediatric patients: a case-control study.

PubMed

Ngerncham, Monawat; Barnhart, Douglas C; Haricharan, Ramanath N; Roseman, Jeffrey M; Georgeson, Keith E; Harmon, Carroll M

2007-09-01

Recurrent gastroesophageal reflux disease (rGERD) is a common problem after fundoplication. Previous studies attempting to identify risk factors for rGERD have failed to control for confounding variables. The purpose of this study was to identify significant risk factors for rGERD after controlling for potential confounding variables. A retrospective, matched case-control study was conducted at a tertiary children's hospital. Cases (n = 116) met 1 of these criteria: reoperation for rGERD, symptomatic rGERD (confirmed by upper gastrointestinal series, esophagogastroduodenoscopy, or pH monitoring), or postoperative reinstitution of antireflux medication for more than 8 weeks. Controls (n = 209) were matched for surgeon, approach (laparoscopic/open), technique (partial/complete), and approximate operative date. Univariate and multivariable associations were analyzed by conditional logistic regression. Significant risk factors for rGERD were age of less than 6 years (odds ratio [OR], 3.6; 95% confidence interval [CI], 1.7-7.5), preoperative hiatal hernia (OR, 3.2; 95% CI, 1.4-7.3), postoperative retching (OR, 5.1; 95% CI, 2.6-10.0), and postoperative esophageal dilatation (OR, 10.8; 95% CI, 1.8-65.4). Interestingly, significant association was not found between neurologic impairment and rGERD after controlling for potential confounding variables. Age of less than 6 years, preoperative hiatal hernia, postoperative retching, and postoperative esophageal dilatation are independently associated with increased risk of rGERD. Neurologic impairment alone does not increase the risk of developing rGERD.

Job Strain and the Cortisol Diurnal Cycle in MESA: Accounting for Between- and Within-Day Variability

PubMed Central

Rudolph, Kara E.; Sánchez, Brisa N.; Stuart, Elizabeth A.; Greenberg, Benjamin; Fujishiro, Kaori; Wand, Gary S.; Shrager, Sandi; Seeman, Teresa; Diez Roux, Ana V.; Golden, Sherita H.

2016-01-01

Evidence of the link between job strain and cortisol levels has been inconsistent. This could be due to failure to account for cortisol variability leading to underestimated standard errors. Our objective was to model the relationship between job strain and the whole cortisol curve, accounting for sources of cortisol variability. Our functional mixed-model approach incorporated all available data—18 samples over 3 days—and uncertainty in estimated relationships. We used employed participants from the Multi-Ethnic Study of Atherosclerosis Stress I Study and data collected between 2002 and 2006. We used propensity score matching on an extensive set of variables to control for sources of confounding. We found that job strain was associated with lower salivary cortisol levels and lower total area under the curve. We found no relationship between job strain and the cortisol awakening response. Our findings differed from those of several previous studies. It is plausible that our results were unique to middle- to older-aged racially, ethnically, and occupationally diverse adults and were therefore not inconsistent with previous research among younger, mostly white samples. However, it is also plausible that previous findings were influenced by residual confounding and failure to propagate uncertainty (i.e., account for the multiple sources of variability) in estimating cortisol features. PMID:26905339

Testing concordance of instrumental variable effects in generalized linear models with application to Mendelian randomization

PubMed Central

Dai, James Y.; Chan, Kwun Chuen Gary; Hsu, Li

2014-01-01

Instrumental variable regression is one way to overcome unmeasured confounding and estimate causal effect in observational studies. Built on structural mean models, there has been considerale work recently developed for consistent estimation of causal relative risk and causal odds ratio. Such models can sometimes suffer from identification issues for weak instruments. This hampered the applicability of Mendelian randomization analysis in genetic epidemiology. When there are multiple genetic variants available as instrumental variables, and causal effect is defined in a generalized linear model in the presence of unmeasured confounders, we propose to test concordance between instrumental variable effects on the intermediate exposure and instrumental variable effects on the disease outcome, as a means to test the causal effect. We show that a class of generalized least squares estimators provide valid and consistent tests of causality. For causal effect of a continuous exposure on a dichotomous outcome in logistic models, the proposed estimators are shown to be asymptotically conservative. When the disease outcome is rare, such estimators are consistent due to the log-linear approximation of the logistic function. Optimality of such estimators relative to the well-known two-stage least squares estimator and the double-logistic structural mean model is further discussed. PMID:24863158

African American Race is an Independent Risk Factor in Survival from Initially Diagnosed Localized Breast Cancer

PubMed Central

Wieder, Robert; Shafiq, Basit; Adam, Nabil

2016-01-01

BACKGROUND: African American race negatively impacts survival from localized breast cancer but co-variable factors confound the impact. METHODS: Data sets were analyzed from the Surveillance, Epidemiology and End Results (SEER) directories from 1973 to 2011 consisting of patients with designated diagnosis of breast adenocarcinoma, race as White or Caucasian, Black or African American, Asian, American Indian or Alaskan Native, Native Hawaiian or Pacific Islander, age, stage I, II or III, grade 1, 2 or 3, estrogen receptor or progesterone receptor positive or negative, marital status as single, married, separated, divorced or widowed and laterality as right or left. The Cox Proportional Hazards Regression model was used to determine hazard ratios for survival. Chi square test was applied to determine the interdependence of variables found significant in the multivariable Cox Proportional Hazards Regression analysis. Cells with stratified data of patients with identical characteristics except African American or Caucasian race were compared. RESULTS: Age, stage, grade, ER and PR status and marital status significantly co-varied with race and with each other. Stratifications by single co-variables demonstrated worse hazard ratios for survival for African Americans. Stratification by three and four co-variables demonstrated worse hazard ratios for survival for African Americans in most subgroupings with sufficient numbers of values. Differences in some subgroupings containing poor prognostic co-variables did not reach significance, suggesting that race effects may be partly overcome by additional poor prognostic indicators. CONCLUSIONS: African American race is a poor prognostic indicator for survival from breast cancer independent of 6 associated co-variables with prognostic significance. PMID:27698895

Demographic factors, fatigue, and driving accidents: An examination of the published literature.

PubMed

Di Milia, Lee; Smolensky, Michael H; Costa, Giovanni; Howarth, Heidi D; Ohayon, Maurice M; Philip, Pierre

2011-03-01

This article reviews the literature pertaining to the association between demographic variables (e.g., age, sex, race, socio-economic status) with fatigue, and when feasible, accident risk. It also explores their potential influence and interaction with some working arrangements, commute time, personality characteristics, and circadian chronotype. Fatigue has been implicated in a range of impairments that can have detrimental effects on individuals, and it is differentially associated with conventional demographic variables. However, several major methodological limitations prevent clear conclusions. First, there is absence of a shared definition both within and across disciplines. Second, although fatigue has been investigated using a variety of diverse designs, they have either been too weak to substantiate causality or lacked ecological validity. Third, while both subjective and objective measures have been used as dependent variables, fatigue has been more often found to be more strongly linked with the former. Fourth, with the exception of age and sex, the influence of other demographic variables is unknown, since they have not yet been concomitantly assessed. In instances when they have been assessed and included in statistical analyses, they are considered as covariates or confounders; thus, their contribution to the outcome variable is controlled for, rather than being a planned aspect of investigation. Because the interaction of demographic factors with fatigue is largely a neglected area of study, we recommend greater interdisciplinary collaborations, incorporation of multiple demographic variables as independent factors, and use of within-participant analyses. These recommendations would provide meaningful results that may be used to inform public policy and preventive strategies. Copyright © 2009 Elsevier Ltd. All rights reserved.

The individualistic fallacy, ecological studies and instrumental variables: a causal interpretation.

PubMed

Loney, Tom; Nagelkerke, Nico J

2014-01-01

The validity of ecological studies in epidemiology for inferring causal relationships has been widely challenged as observed associations could be biased by the Ecological Fallacy. We reconsider the important design components of ecological studies, and discuss the conditions that may lead to spurious associations. Ecological associations are useful and valid when the ecological exposures can be interpreted as Instrumental Variables. A suitable example may be a time series analysis of environmental pollution (e.g. particulate matter with an aerodynamic diameter of <10 micrometres; PM10) and health outcomes (e.g. hospital admissions for acute myocardial infarction) as environmental pollution levels are a cause of individual exposure levels and not just an aggregate measurement. Ecological exposures may also be employed in situations (perhaps rare) where individual exposures are known but their associations with health outcomes are confounded by unknown or unquantifiable factors. Ecological associations have a notorious reputation in epidemiology and individualistic associations are considered superior to ecological associations because of the "ecological fallacy". We have argued that this is incorrect in situations in which ecological or aggregate exposures can serve as an instrumental variable and associations between individual exposure and outcome are likely to be confounded by unmeasured variables.

Tracking Central Hypovolemia with ECG in Humans: Cautions for the Use of Heart Period Variability in Patient Monitoring

DTIC Science & Technology

2010-06-01

without influences that may confound the re- sults (e.g., pain, anxiety , transport conditions, caregiver in- terventions). Second, rather than being...32. Ryan KL, Rickards CA, Muniz GW, Moralez G, Convertino VA: Interindi- vidual variability in heart rate variability ( HRV ) and complexity measure...Raimondi G, Legramante JM, Macerata A: Revisiting the potential of time-domain indexes in short-term HRV analysis. Biomed Tech (Berl) 51:190Y193, 2006

Gender-related mental health differences between refugees and non-refugee immigrants - a cross-sectional register-based study

PubMed Central

2011-01-01

Background Being an immigrant in a high-income country is a risk factor for severe mental ill health. Studies on mental ill health among immigrants have found significant differences in mental health outcome between immigrants from high income countries and low-income countries. Being an asylum seeker or a refugee is also associated with mental ill health. This study aimed to assess if there is a difference in mental ill health problems between male and female refugee and non-refugee immigrants from six low-income countries in Sweden. Methods A cross-sectional, population-based study design was used comparing refugees with non-refugees. The study size was determined by the number of persons in Sweden fulfilling the inclusion criteria at the time of the study during 2006. Outcome: Mental ill health, as measured with the proxy variable psychotropic drugs purchased. Refugee/Non-refugee: Sweden grants asylum to refugees according to the Geneva Convention and those with a well-grounded fear of death penalty, torture or who need protection due to an internal or external armed conflict or an environmental disaster. The non-refugees were all family members of those granted asylum in Sweden. Covariates: Gender and origin. Potential confounders: Age, marital status, education and duration of stay in Sweden. Background variables were analysed using chi square tests. The association between outcome, exposure and possible confounders was analysed using logistic regression analyses. Multiple logistic regression analysis was used to adjust for potential confounders. Results The study population comprised 43,168 refugees and non-refugees, of whom 20,940 (48.5%) were women and 24,403 (56.5%) were refugees. Gender, age, origin, marital status and education were all associated with the outcome. For female, but not male, refugees there was a significantly higher likelihood of purchasing psychotropic drugs than non-refugees (OR = 1.27, 95% CI = 1.15 - 1.40). Conclusions Female refugees from low-income countries seem to be a risk group among immigrant women from low-income countries, whereas male refugees had the same risk patterns as non-refugee immigrants from low-income countries. This underlines the need for training of clinicians in order to focus on pre-migration stress and the asylum process, among female newcomers. PMID:21435212

Uncovering cyanobacteria ecological networks from long-term monitoring data using Granger causality analysis

NASA Astrophysics Data System (ADS)

Nelson, N.; Munoz-Carpena, R.; Kaplan, D. A.; Phlips, E. J.

2016-12-01

In many aquatic systems, cyanobacteria form harmful blooms capable of producing toxins, prompting hypoxia, and/or introducing internal nitrogen loads via N2-fixation, among other impacts. Traditionally, system-specific cyanobacteria drivers are determined by performing controlled experiments and bioassays, but these approaches may neglect the influences of confounding factors and over assign importance to only those variables considered within experimental designs. For example, a bioassay may conclude that the cyanobacteria in a particular system are limited by phosphorus, but will not explicitly take into account the role of flow as a control on phosphorus delivery. This study aims to address this analytical gap by identifying environmental controls on cyanobacteria while removing the effects of potentially confounding variables. In the present work, we evaluate a unique long-term (17 year) dataset composed of monthly observations of phytoplankton and zooplankton species abundances, water quality constituents, and hydrologic variables from Lake George, a flow-through lake of the St. Johns River (FL) impacted by cyanobacterial blooms. Using conditional Granger causality analysis, a time series approach that infers causality while removing the effects of confounding variables, data were evaluated to identify biological and physicochemical drivers of cyanobacteria. The analysis was performed for three response variable sets: total cyanobacteria, N2-fixers and non-fixers, and cyanobacteria genera. Results depicted increasing levels of ecological complexity as subdivisions of cyanobacteria became more detailed; whereas causal networks produced from analyses of cyanobacteria genera provided novel insights relevant for management (i.e. nutrients, flow), the total cyanobacteria network only included water temperature as a significant driver. Additionally, the more detailed cyanobacteria subdivisions uncovered that N2-fixation was only evident with the earliest season bloomer, thus indicating that early season bloomers may be facilitating later-season growth. These findings highlight the importance of detailed monitoring efforts, and indicate that greater emphasis needs to be placed on the role of early bloomers in phytoplankton dynamics, as it relates to management efforts.

The role of prenatal care and social risk factors in the relationship between immigrant status and neonatal morbidity: a retrospective cohort study.

PubMed

Paz-Zulueta, María; Llorca, Javier; Sarabia-Lavín, Raquel; Bolumar, Francisco; Rioja, Luis; Delgado, Abraham; Santibáñez, Miguel

2015-01-01

Literature evaluating association between neonatal morbidity and immigrant status presents contradictory results. Poorer compliance with prenatal care and greater social risk factors among immigrants could play roles as major confounding variables, thus explaining contradictions. We examined whether prenatal care and social risk factors are confounding variables in the relationship between immigrant status and neonatal morbidity. Retrospective cohort study: 231 pregnant African immigrant women were recruited from 2007-2010 in northern Spain. A Spanish population sample was obtained by simple random sampling at 1:3 ratio. Immigrant status (Spanish, Sub-Saharan and Northern African), prenatal care (Kessner Index adequate, intermediate or inadequate), and social risk factors were treated as independent variables. Low birth weight (LBW < 2500 grams) and preterm birth (< 37 weeks) were collected as neonatal morbidity variables. Crude and adjusted odds ratios (OR) were estimated by unconditional logistic regression with 95% confidence intervals (95% CI). Positive associations between immigrant women and higher risk of neonatal morbidity were obtained. Crude OR for preterm births in Northern Africans with respect to nonimmigrants was 2.28 (95% CI: 1.04-5.00), and crude OR for LBW was 1.77 (95% CI: 0.74-4.22). However, after adjusting for prenatal care and social risk factors, associations became protective: adjusted OR for preterm birth = 0.42 (95% CI: 0.14-1.32); LBW = 0.48 (95% CI: 0.15-1.52). Poor compliance with prenatal care was the main independent risk factor associated with both preterm birth (adjusted OR inadequate care = 17.05; 95% CI: 3.92-74.24) and LBW (adjusted OR inadequate care = 6.25; 95% CI: 1.28-30.46). Social risk was an important independent risk factor associated with LBW (adjusted OR = 5.42; 95% CI: 1.58-18.62). Prenatal care and social risk factors were major confounding variables in the relationship between immigrant status and neonatal morbidity.

Confounding and Statistical Significance of Indirect Effects: Childhood Adversity, Education, Smoking, and Anxious and Depressive Symptomatology.

PubMed

Sheikh, Mashhood Ahmed

2017-01-01

The life course perspective, the risky families model, and stress-and-coping models provide the rationale for assessing the role of smoking as a mediator in the association between childhood adversity and anxious and depressive symptomatology (ADS) in adulthood. However, no previous study has assessed the independent mediating role of smoking in the association between childhood adversity and ADS in adulthood. Moreover, the importance of mediator-response confounding variables has rarely been demonstrated empirically in social and psychiatric epidemiology. The aim of this paper was to (i) assess the mediating role of smoking in adulthood in the association between childhood adversity and ADS in adulthood, and (ii) assess the change in estimates due to different mediator-response confounding factors (education, alcohol intake, and social support). The present analysis used data collected from 1994 to 2008 within the framework of the Tromsø Study ( N = 4,530), a representative prospective cohort study of men and women. Seven childhood adversities (low mother's education, low father's education, low financial conditions, exposure to passive smoke, psychological abuse, physical abuse, and substance abuse distress) were used to create a childhood adversity score. Smoking status was measured at a mean age of 54.7 years (Tromsø IV), and ADS in adulthood was measured at a mean age of 61.7 years (Tromsø V). Mediation analysis was used to assess the indirect effect and the proportion of mediated effect (%) of childhood adversity on ADS in adulthood via smoking in adulthood. The test-retest reliability of smoking was good (Kappa: 0.67, 95% CI: 0.63; 0.71) in this sample. Childhood adversity was associated with a 10% increased risk of smoking in adulthood (Relative risk: 1.10, 95% CI: 1.03; 1.18), and both childhood adversity and smoking in adulthood were associated with greater levels of ADS in adulthood ( p < 0.001). Smoking in adulthood did not significantly mediate the association between childhood adversity and ADS in adulthood. However, when education was excluded as a mediator-response confounding variable, the indirect effect of childhood adversity on ADS in adulthood was statistically significant ( p < 0.05). This study shows that a careful inclusion of potential confounding variables is important when assessing mediation.

Confounding and Statistical Significance of Indirect Effects: Childhood Adversity, Education, Smoking, and Anxious and Depressive Symptomatology

PubMed Central

Sheikh, Mashhood Ahmed

2017-01-01

The life course perspective, the risky families model, and stress-and-coping models provide the rationale for assessing the role of smoking as a mediator in the association between childhood adversity and anxious and depressive symptomatology (ADS) in adulthood. However, no previous study has assessed the independent mediating role of smoking in the association between childhood adversity and ADS in adulthood. Moreover, the importance of mediator-response confounding variables has rarely been demonstrated empirically in social and psychiatric epidemiology. The aim of this paper was to (i) assess the mediating role of smoking in adulthood in the association between childhood adversity and ADS in adulthood, and (ii) assess the change in estimates due to different mediator-response confounding factors (education, alcohol intake, and social support). The present analysis used data collected from 1994 to 2008 within the framework of the Tromsø Study (N = 4,530), a representative prospective cohort study of men and women. Seven childhood adversities (low mother's education, low father's education, low financial conditions, exposure to passive smoke, psychological abuse, physical abuse, and substance abuse distress) were used to create a childhood adversity score. Smoking status was measured at a mean age of 54.7 years (Tromsø IV), and ADS in adulthood was measured at a mean age of 61.7 years (Tromsø V). Mediation analysis was used to assess the indirect effect and the proportion of mediated effect (%) of childhood adversity on ADS in adulthood via smoking in adulthood. The test-retest reliability of smoking was good (Kappa: 0.67, 95% CI: 0.63; 0.71) in this sample. Childhood adversity was associated with a 10% increased risk of smoking in adulthood (Relative risk: 1.10, 95% CI: 1.03; 1.18), and both childhood adversity and smoking in adulthood were associated with greater levels of ADS in adulthood (p < 0.001). Smoking in adulthood did not significantly mediate the association between childhood adversity and ADS in adulthood. However, when education was excluded as a mediator-response confounding variable, the indirect effect of childhood adversity on ADS in adulthood was statistically significant (p < 0.05). This study shows that a careful inclusion of potential confounding variables is important when assessing mediation. PMID:28824498

Case-control studies of the efficacy of cancer screening: overcoming bias from nonrandom patterns of screening.

PubMed

Weiss, Noel S; Dhillon, Preet K; Etzioni, Ruth

2004-07-01

A case-control study of the efficacy of cancer screening, like any other case-control study, must deal with potential confounding. There are 2 categories of confounding variables that pose special problems for studies of screening: (1) age and calendar time resulting from different temporal distributions of screening between cases and controls irrespective of whether the screening test leads to a reduction in mortality; and (2) the administration of other screening tests for the cancer in question when it is not clear whether the result of the other test had a bearing on the decision to order the test under study. We describe circumstances in which confounding from these sources can be dealt with satisfactorily by means of restriction or adjustment, and other circumstances in which it cannot. Copyright 2004 Lippincott Williams and Wilkins

Pot binding as a variable confounding plant phenotype: theoretical derivation and experimental observations.

PubMed

Sinclair, Thomas R; Manandhar, Anju; Shekoofa, Avat; Rosas-Anderson, Pablo; Bagherzadi, Laleh; Schoppach, Remy; Sadok, Walid; Rufty, Thomas W

2017-04-01

Theoretical derivation predicted growth retardation due to pot water limitations, i.e., pot binding. Experimental observations were consistent with these limitations. Combined, these results indicate a need for caution in high-throughput screening and phenotyping. Pot experiments are a mainstay in many plant studies, including the current emphasis on developing high-throughput, phenotyping systems. Pot studies can be vulnerable to decreased physiological activity of the plants particularly when pot volume is small, i.e., "pot binding". It is necessary to understand the conditions under which pot binding may exist to avoid the confounding influence of pot binding in interpreting experimental results. In this paper, a derivation is offered that gives well-defined conditions for the occurrence of pot binding based on restricted water availability. These results showed that not only are pot volume and plant size important variables, but the potting media is critical. Artificial potting mixtures used in many studies, including many high-throughput phenotyping systems, are particularly susceptible to the confounding influences of pot binding. Experimental studies for several crop species are presented that clearly show the existence of thresholds of plant leaf area at which various pot sizes and potting media result in the induction of pot binding even though there may be no immediate, visual plant symptoms. The derivation and experimental results showed that pot binding can readily occur in plant experiments if care is not given to have sufficiently large pots, suitable potting media, and maintenance of pot water status. Clear guidelines are provided for avoiding the confounding effects of water-limited pot binding in studying plant phenotype.

Simpson's paradox: A statistician's case study.

PubMed

Chu, Kevin H; Brown, Nathan J; Pelecanos, Anita; Brown, Anthony Ft

2018-02-26

Gender equality and workforce diversity has recently been in the forefront of College discussions. Reasons for the difference between various groups may not be as they initially appeared. The results of comparing the outcome between two groups can sometimes be confounded and even reversed by an unrecognised third variable. This concept is known as Simpson's Paradox, and is illustrated here using a renowned case study on potential gender bias for acceptance to Graduate School at the University of California, Berkeley.  The investigation showed that males were 1.8 times more likely to be admitted to Graduate School than females in 1973. Initially it appeared that women were discriminated against in the selection process. However, when admissions were re-examined at individual Departments of the School, admission tended to be better for women than men in four of six Departments. This contradiction or paradox tells us that the association between admission and gender was dependent upon on Department.  The confounding effect of Department was defined by two characteristics. Firstly, a strong association between Department and admission: some Departments admitted much smaller percentages of applicants than others. Secondly, a strong association between Department and gender: females tended to apply to Departments with lower admission rates.  The explanation of differences between groups can be multifactorial. A search for possible confounders will assist in this understanding. This could apply whenever two groups initially appear to differ, but on closer analysis this difference is either unfounded, or even reversed by reference to a third, confounding variable. © 2018 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine.

Drug induced liver injury with analysis of alternative causes as confounding variables.

PubMed

Teschke, Rolf; Danan, Gaby

2018-04-01

Drug-induced liver injury (DILI) is rare compared to the worldwide frequent acute or chronic liver diseases. Therefore, patients included in series of suspected DILI are at high risk of not having DILI, whereby alternative causes may confound the DILI diagnosis. The aim of this review is to evaluate published case series of DILI for alternative causes. Relevant studies were identified using a computerized search of the Medline database for publications from 1993 through 30 October 2017. We used the following terms: drug hepatotoxicity, drug induced liver injury, hepatotoxic drugs combined with diagnosis, causality assessment and alternative causes. Alternative causes as variables confounding the DILI diagnosis emerged in 22 published DILI case series, ranging from 4 to 47%. Among 13 335 cases of suspected DILI, alternative causes were found to be more likely in 4555 patients (34.2%), suggesting that the suspected DILI was probably not DILI. Biliary diseases such as biliary obstruction, cholangitis, choledocholithiasis, primary biliary cholangitis and primary sclerosing cholangitis were among the most missed diagnoses. Alternative causes included hepatitis B, C and E, cytomegalovirus, Epstein-Barr virus, ischemic hepatitis, cardiac hepatopathy, autoimmune hepatitis, nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, and alcoholic liver disease. In more than one-third of published global DILI case series, alternative causes as published in these reports confounded the DILI diagnosis. In the future, published DILI case series should include only patients with secured DILI diagnosis, preferentially established by prospective use of scored items provided by robust diagnostic algorithms such as the updated Roussel Uclaf causality assessment method. © 2018 The British Pharmacological Society.

Betel Nut Usage Is a Major Risk Factor for Coronary Artery Disease

PubMed Central

Khan, Muhammad Shahzeb; Bawany, Faizan Imran; Ahmed, Muhammad Umer; Hussain, Mehwish; Khan, Asadullah; Lashari, Muhammad Nawaz

2014-01-01

Aim: The objective of our study was to assess betel nut usage as one of the major risk factors associated with coronary artery disease. Methods: This case control study consisted of 300 controls and 300 cases. A structured questionnaire was administered to the participants to assess consumption of betel nut and confounding variables. A respondent was considered a regular consumer of betel nut if he/she consumed one or more pieces of betel nut every day for a period of greater than 6 months. Results: About 8 in 10 betel nut chewers developed coronary artery disease. After adjusting for diabetes and hypertension, the odds ratio analysis depicted 7.72 times greater likelihood for coronary artery disease in patients who chewed betel nut for more than 10 years. Conclusion: Our study concludes that betel nut chewing is a significant risk factor leading to the development of coronary artery disease. PMID:24576380

Posttraumatic Stress Disorder, Cardiovascular and Metabolic Disease: A Review of the Evidence

PubMed Central

Dedert, Eric A.; Calhoun, Patrick S.; Watkins, Lana L.; Sherwood, Andrew; Beckham, Jean C.

2011-01-01

Background Posttraumatic stress disorder (PTSD) is a significant risk factor for cardiovascular and metabolic disease. Purpose The purpose of the current review is to evaluate the evidence suggesting that PTSD increases cardiovascular and metabolic risk factors, and to identify possible biomarkers and psychosocial characteristics and behavioral variables that are associated with these outcomes. Methods A systematic literature search in the period of 2002–2009 for PTSD, cardiovascular disease, and metabolic disease was conducted. Results The literature search yielded 78 studies on PTSD and cardiovascular/metabolic disease and biomarkers. Conclusions Although the available literature suggests an association of PTSD with cardiovascular disease and biomarkers, further research must consider potential confounds, incorporate longitudinal designs, and conduct careful PTSD assessments in diverse samples to address gaps in the research literature. Research on metabolic disease and biomarkers suggests an association with PTSD, but has not progressed as far as the cardiovascular research. PMID:20174903

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 2, Diagnostic Performance, Confounders, and Future Directions

PubMed Central

Tang, An; Cloutier, Guy; Szeverenyi, Nikolaus M.; Sirlin, Claude B.

2016-01-01

OBJECTIVE The purpose of the article is to review the diagnostic performance of ultrasound and MR elastography techniques for detection and staging of liver fibrosis, the main current clinical applications of elastography in the abdomen. CONCLUSION Technical and instrument-related factors and biologic and patient-related factors may constitute potential confounders of stiffness measurements for assessment of liver fibrosis. Future developments may expand the scope of elastography for monitoring liver fibrosis and predict complications of chronic liver disease. PMID:25905762

Ecomorphology and phylogenetic risk: Implications for habitat reconstruction using fossil bovids.

PubMed

Scott, Robert S; Barr, W Andrew

2014-08-01

Reconstructions of paleohabitats are necessary aids in understanding hominin evolution. The morphology of species from relevant sites, understood in terms of functional relationships to habitat (termed ecomorphology), offers a direct link to habitat. Bovids are a speciose radiation that includes many habitat specialists and are abundant in the fossil record. Thus, bovids are extremely common in ecomorphological analyses. However, bovid phylogeny and habitat preference are related, which raises the possibility that analyses linking habitat with morphology are not 'taxon free' but 'taxon-dependent.' Here we analyze eight relative dimensions and one shape index of the metatarsal for a sample of 72 bovid species and one antilocaprid. The selected variables have been previously shown to have strong associations with habitat and to have functional explanations for these associations. Phylogenetic generalized least squares analyses of these variables, including habitat and size, resulted in estimates for the parameter lambda (used to model phylogenetic signal) varying from zero to one. Thus, while phylogeny, morphology, and habitat all march together among the bovids, the odds that phylogeny confounds ecomorphological analyses may vary depending on particular morphological characteristics. While large values of lambda do not necessarily indicate that habitat differences are unimportant drivers of morphology, we consider the low value of lambda for relative metatarsal width suggestive that conclusions about habitat built on observations of this particular morphology carry with them less 'phylogenetic risk.' We suggest that the way forward for ecomorphology is grounded in functionally relevant observations and careful consideration of phylogeny designed to bracket probable habitat preferences appropriately. Separate consideration of different morphological variables may help to determine the level of 'phylogenetic risk' attached to conclusions linking habitat and morphology. Copyright © 2014 Elsevier Ltd. All rights reserved.

Long-Term Coarse Particulate Matter Exposure and Heart Rate Variability in the Multi-Ethnic Study of Atherosclerosis (MESA)

PubMed Central

Adhikari, Richa; D’Souza, Jennifer; Solimon, Elsayed Z.; Burke, Gregory L.; Daviglus, Martha; Jacobs, David R.; Park, Sung Kyun; Sheppard, Lianne; Thorne, Peter S.; Kaufman, Joel D.; Larson, Timothy V.; Adar, Sara D.

2017-01-01

Background Reduced heart rate variability, a marker of impaired cardiac autonomic function, has been linked to short-term exposure to airborne particles. This research adds to the literature by examining associations with long-term exposures to coarse particles (PM10-2.5). Methods Using electrocardiogram recordings from 2,780 participants (45-84 years) from three Multi-Ethnic Study of Atherosclerosis sites, we assessed the standard deviation of normal-to-normal intervals (SDNN) and root-mean square differences of successive normal-to-normal intervals (rMSSD) at a baseline (2000-2002) and follow-up (2010-2012) examination (mean visits/person=1.5). Annual average concentrations of PM10-2.5 mass, copper, zinc, phosphorus, silicon, and endotoxin were estimated using site-specific spatial prediction models. We assessed associations for baseline heart rate variability and rate of change in heart rate variability over time using multivariable mixed models adjusted for time, sociodemographic, lifestyle, health, and neighborhood confounders, including co-pollutants. Results In our primary models adjusted for demographic and lifestyle factors and site, PM10-2.5 mass was associated with 1.0% (95% CI: -4.1, 2.1%) lower SDNN levels per interquartile range of 2 μg/m3. Stronger associations, however, were observed prior to site adjustment and with increasing residential stablity. Similar patterns were found for rMSSD. We found little evidence for associations with other chemical species and with with the rate of change in heart rate variability, though endotoxin was associated with increasing heart rate variability over time. Conclusion We found only weak evidence that long-term PM10-2.5 exposures are associated with lowered heart rate variability. Stronger associations among residentially stable individuals suggest that confirmatory studies are needed. PMID:27035690

Missing variables: how exclusion of human resources policy information confounds research connecting health and business outcomes.

PubMed

Lynch, Wendy D; Sherman, Bruce W

2014-01-01

When corporate health researchers examine the effects of health on business outcomes or the effect of health interventions on health and business outcomes, results will necessarily be confounded by the corporate environment(s) in which they are studied. In this research setting, most studies control for factors traditionally identified in public health, such as demographics and health status. Nevertheless, often overlooked is the extent to which company policies can also independently impact health care cost, work attendance, and productivity outcomes. With changes in employment and benefits practices resulting from health care reform, including incentives and plan design options, consideration of these largely neglected variables in research design has become increasingly important. This commentary summarizes existing knowledge regarding the implications of policy variations in research outcomes and provides a framework for incorporating them into future employer-based research.

Instrumental variable methods in comparative safety and effectiveness research.

PubMed

Brookhart, M Alan; Rassen, Jeremy A; Schneeweiss, Sebastian

2010-06-01

Instrumental variable (IV) methods have been proposed as a potential approach to the common problem of uncontrolled confounding in comparative studies of medical interventions, but IV methods are unfamiliar to many researchers. The goal of this article is to provide a non-technical, practical introduction to IV methods for comparative safety and effectiveness research. We outline the principles and basic assumptions necessary for valid IV estimation, discuss how to interpret the results of an IV study, provide a review of instruments that have been used in comparative effectiveness research, and suggest some minimal reporting standards for an IV analysis. Finally, we offer our perspective of the role of IV estimation vis-à-vis more traditional approaches based on statistical modeling of the exposure or outcome. We anticipate that IV methods will be often underpowered for drug safety studies of very rare outcomes, but may be potentially useful in studies of intended effects where uncontrolled confounding may be substantial.

Controlling for seasonal patterns and time varying confounders in time-series epidemiological models: a simulation study.

PubMed

Perrakis, Konstantinos; Gryparis, Alexandros; Schwartz, Joel; Le Tertre, Alain; Katsouyanni, Klea; Forastiere, Francesco; Stafoggia, Massimo; Samoli, Evangelia

2014-12-10

An important topic when estimating the effect of air pollutants on human health is choosing the best method to control for seasonal patterns and time varying confounders, such as temperature and humidity. Semi-parametric Poisson time-series models include smooth functions of calendar time and weather effects to control for potential confounders. Case-crossover (CC) approaches are considered efficient alternatives that control seasonal confounding by design and allow inclusion of smooth functions of weather confounders through their equivalent Poisson representations. We evaluate both methodological designs with respect to seasonal control and compare spline-based approaches, using natural splines and penalized splines, and two time-stratified CC approaches. For the spline-based methods, we consider fixed degrees of freedom, minimization of the partial autocorrelation function, and general cross-validation as smoothing criteria. Issues of model misspecification with respect to weather confounding are investigated under simulation scenarios, which allow quantifying omitted, misspecified, and irrelevant-variable bias. The simulations are based on fully parametric mechanisms designed to replicate two datasets with different mortality and atmospheric patterns. Overall, minimum partial autocorrelation function approaches provide more stable results for high mortality counts and strong seasonal trends, whereas natural splines with fixed degrees of freedom perform better for low mortality counts and weak seasonal trends followed by the time-season-stratified CC model, which performs equally well in terms of bias but yields higher standard errors. Copyright © 2014 John Wiley & Sons, Ltd.

No association between partial depopulation and Campylobacter spp. colonization of Dutch broiler flocks.

PubMed

Russa, A D; Bouma, A; Vernooij, J C M; Jacobs-Reitsma, W; Stegeman, J A

2005-01-01

To determine whether an association exists between partial depopulation of a flock and increased Campylobacter colonization in that flock. Data from 1737 flocks of two Dutch integrators were used. Flocks that experienced partial depopulation were defined as 'exposed' and those that did not as 'nonexposed'. Multivariable modelling was accomplished with, in addition to 'exposure', the independent variables 'age of broilers at slaughter' and 'season' to adjust for possible confounding. The response variable was 'Campylobacter colonization'. The odds ratio (OR) for partial depopulation for integrator A was 0.8 [95% CI (0.4, 1.8)]; for integrator B the OR = 0.8 [95% CI (0.5, 1.3)]. Age and season were confounders: the difference in Campylobacter status between exposed and nonexposed flocks of integrator A could be explained by both variables; for integrator B, only season was associated with Campylobacter status. We found no significant association between partial depopulation and an increased risk of Campylobacter colonization among broiler flocks at final depopulation. This study demonstrates that Campylobacter colonization in a broiler flock is not influenced by the partial depopulation of that flock.

African ancestry, lung function and the effect of genetics

PubMed Central

Wehrmeister, Fernando C.; Hartwig, Fernando P.; Perez-Padilla, Rogelio; Gigante, Denise P.; Barros, Fernando C.; Oliveira, Isabel O.; Ferreira, Gustavo D.; Horta, Bernardo L.

2015-01-01

African-Americans have smaller lung function compared with European-Americans. The aim of this study was to disentangle the contribution of genetics from other variables on lung function. A cohort was followed from birth to 30 years of age in Brazil. Several variables were collected: genomic analysis based on DNA; forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) obtained by spirometry; height measured by anthropometrists; and thorax circumference evaluated by photonic scanner. Crude and adjusted linear regression models were calculated according to African ancestry. The sample comprised 2869 participants out of 3701 members of the cohort. Males with higher African ancestry by DNA analysis had a smaller FEV1 (−0.13 L, 95% CI −0.23– −0.03 L) and FVC (−0.21 L, 95% CI −0.32– −0.09 L) compared with those with less African ancestry, having accounted for height, sitting to standing height ratio and other confounders. Similar effects were seen in females. After adjustment, ancestry remained significantly associated with lung function, but the large effect of adjustment for confounding among males (but not females) does not allow us to exclude the possibility that residual confounding may still account for these findings. PMID:25700383

Reporting of research quality characteristics of studies published in 6 major clinical dental specialty journals.

PubMed

Pandis, Nikolaos; Polychronopoulou, Argy; Madianos, Phoebus; Makou, Margarita; Eliades, Theodore

2011-06-01

The objective of this article was to record reporting characteristics related to study quality of research published in major specialty dental journals with the highest impact factor (Journal of Endodontics, Journal of Oral and Maxillofacial Surgery, American Journal of Orthodontics and Dentofacial Orthopedics; Pediatric Dentistry, Journal of Clinical Periodontology, and International Journal of Prosthetic Dentistry). The included articles were classified into the following 3 broad subject categories: (1) cross-sectional (snap-shot), (2) observational, and (3) interventional. Multinomial logistic regression was conducted for effect estimation using the journal as the response and randomization, sample calculation, confounding discussed, multivariate analysis, effect measurement, and confidence intervals as the explanatory variables. The results showed that cross-sectional studies were the dominant design (55%), whereas observational investigations accounted for 13%, and interventions/clinical trials for 32%. Reporting on quality characteristics was low for all variables: random allocation (15%), sample size calculation (7%), confounding issues/possible confounders (38%), effect measurements (16%), and multivariate analysis (21%). Eighty-four percent of the published articles reported a statistically significant main finding and only 13% presented confidence intervals. The Journal of Clinical Periodontology showed the highest probability of including quality characteristics in reporting results among all dental journals. Copyright © 2011 Elsevier Inc. All rights reserved.

Demographic factors influencing the GH system: Implications for the detection of GH doping in sport.

PubMed

Nelson, Anne E; Ho, Ken K Y

2009-08-01

Application of methods for detecting GH doping depend on being able to discriminate between abnormal levels due to doping and normal physiological levels of circulating proteins that change in response to exogenous administration. Constituents of the IGF and collagen systems have been shown to be promising markers of GH abuse. Their ultimate utility, however, depends on identification of the factors that regulate their concentrations in blood. Among these are demographic factors that are known to influence these markers in the general population. In a large cross-sectional study of the GH-responsive markers in over 1000 elite athletes from 12 countries representing 4 major ethnic groups and 10 sport types, we have shown that there is a significant negative correlation between age and all the IGF and collagen markers we studied, with a rapid decrease in early adolescence. Age was the major contribution to the variability, equivalent to >80% of the attributable variation in IGF-I and the collagen markers. The IGF axis markers were all significantly higher in women, and the collagen markers significantly higher in men, however, the contribution of gender was smaller than that of age, except for IGFBP-3 and ALS. BMI had a minor contribution to variability of the GH-responsive markers. After adjustment for the confounding influences of age, gender and BMI, the effect of ethnicity in elite athletes was trivial except for IGFBP-3 and ALS, which were both lower in Africans and higher in Caucasians. Compared to age and gender, the contribution of sport type was also modest. Our findings on the influence of age, gender, BMI and sport type have also been confirmed in a study of mostly Caucasian elite athletes in the post-competition setting. In conclusion, age and gender are the major determinants of variability for IGF-I and the collagen markers, whereas ethnicity and sport type have a minor influence. Therefore, a test based on IGF-I and the collagen markers must take age into account for men and women, and ethnicity and sport type are unlikely to be confounders for these markers.

Identification of biological traits associated with differences in residual energy intake among lactating Holstein cows.

PubMed

Fischer, A; Delagarde, R; Faverdin, P

2018-05-01

Residual feed intake, which is usually used to estimate individual variation of feed efficiency, requires frequent and accurate measurements of individual feed intake to be carried out. Developing a breeding scheme based on residual feed intake in dairy cows is therefore complicated, especially because feed intake is not measurable for a large population. Another solution could be to focus on biological determinants of feed efficiency, which could potentially be directly and broadband measurable on farm. Several phenotypes have been identified in literature as being associated with differences in feed efficiency. The present study therefore aims to identify which biological mechanisms are associated with residual energy intake (REI) differences among dairy cows. Several candidate phenotypes were recorded frequently and simultaneously throughout the first 238 d in milk for 60 Holstein cows fed on a constant diet based on maize silage. A multiple linear regression of the 238 d in milk average of net energy intake was fitted on the 238 d in milk averages for milk energy output, metabolic body weight, the sum over the 238 d in milk of both, body condition score loss and gain, and the residuals were defined as REI. A partial least square regression was fitted over all biological traits to explain REI variability. Linear multiple regression explained 93.6% of net energy intake phenotypic variation, with 65.5% associated with lactation requirement, 23.2% with maintenance, and 4.9% with body reserves change; the 6.4% residuals represented REI. Overall, measured biological traits contributed to 58.9% of REI phenotypic variability, which were mainly explained by activity (26.5%) and feeding behavior (21.3%). However, apparent confounding was observed between behavior, activity, digestibility, and rumen-temperature variables. Drawing a conclusion on biological traits that explain feed efficiency differences among dairy cows was not possible due to this apparent confounding between the measured variables. Further investigation is needed to validate these results and to characterize the causal relationship of feed efficiency with feeding behavior, digestibility, body reserves change, activity, and rumen temperature. The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Confounding Problems in Multifactor AOV When Using Several Organismic Variables of Limited Reliability

ERIC Educational Resources Information Center

Games, Paul A.

1975-01-01

A brief introduction is presented on how multiple regression and linear model techniques can handle data analysis situations that most educators and psychologists think of as appropriate for analysis of variance. (Author/BJG)

Beyond total treatment effects in randomised controlled trials: Baseline measurement of intermediate outcomes needed to reduce confounding in mediation investigations.

PubMed

Landau, Sabine; Emsley, Richard; Dunn, Graham

2018-06-01

Random allocation avoids confounding bias when estimating the average treatment effect. For continuous outcomes measured at post-treatment as well as prior to randomisation (baseline), analyses based on (A) post-treatment outcome alone, (B) change scores over the treatment phase or (C) conditioning on baseline values (analysis of covariance) provide unbiased estimators of the average treatment effect. The decision to include baseline values of the clinical outcome in the analysis is based on precision arguments, with analysis of covariance known to be most precise. Investigators increasingly carry out explanatory analyses to decompose total treatment effects into components that are mediated by an intermediate continuous outcome and a non-mediated part. Traditional mediation analysis might be performed based on (A) post-treatment values of the intermediate and clinical outcomes alone, (B) respective change scores or (C) conditioning on baseline measures of both intermediate and clinical outcomes. Using causal diagrams and Monte Carlo simulation, we investigated the performance of the three competing mediation approaches. We considered a data generating model that included three possible confounding processes involving baseline variables: The first two processes modelled baseline measures of the clinical variable or the intermediate variable as common causes of post-treatment measures of these two variables. The third process allowed the two baseline variables themselves to be correlated due to past common causes. We compared the analysis models implied by the competing mediation approaches with this data generating model to hypothesise likely biases in estimators, and tested these in a simulation study. We applied the methods to a randomised trial of pragmatic rehabilitation in patients with chronic fatigue syndrome, which examined the role of limiting activities as a mediator. Estimates of causal mediation effects derived by approach (A) will be biased if one of the three processes involving baseline measures of intermediate or clinical outcomes is operating. Necessary assumptions for the change score approach (B) to provide unbiased estimates under either process include the independence of baseline measures and change scores of the intermediate variable. Finally, estimates provided by the analysis of covariance approach (C) were found to be unbiased under all the three processes considered here. When applied to the example, there was evidence of mediation under all methods but the estimate of the indirect effect depended on the approach used with the proportion mediated varying from 57% to 86%. Trialists planning mediation analyses should measure baseline values of putative mediators as well as of continuous clinical outcomes. An analysis of covariance approach is recommended to avoid potential biases due to confounding processes involving baseline measures of intermediate or clinical outcomes, and not simply for increased precision.

Postpartum depression among women with unintended pregnancy

PubMed Central

Brito, Cynthia Nunes de Oliveira; Alves, Sandra Valongueiro; Ludermir, Ana Bernarda; de Araújo, Thália Velho Barreto

2015-01-01

OBJECTIVE To analyze the association between unintended pregnancy and postpartum depression. METHODS This is a prospective cohort study conducted with 1,121 pregnant aged 18 to 49 years, who attended the prenatal program devised by the Brazilian Family Health Strategy, Recife, PE, Northeastern Brazil, between July 2005 and December 2006. We interviewed 1,121 women during pregnancy and 1,057 after childbirth. Unintended pregnancy was evaluated during the first interview and postpartum depression symptoms were assessed using the Edinburgh Postnatal Depression Screening Scale. The crude and adjusted odds ratios for the studied association were estimated using logistic regression analysis. RESULTS The frequency for unintended pregnancy was 60.2%; 25.9% presented postpartum depression symptoms. Those who had unintended pregnancies had a higher likelihood of presenting this symptoms, even after adjusting for confounding variables (OR = 1.48; 95%CI 1.09;2.01). When the Self Reporting Questionnaire (SRQ-20) variable was included, the association decreased, however, remained statistically significant (OR = 1.42; 95%CI 1.03;1.97). CONCLUSIONS Unintended pregnancy showed association with subsequent postpartum depressive symptoms. This suggests that high values in Edinburgh Postnatal Depression Screening Scale may result from unintended pregnancy. PMID:26083941

Prediction of Methotrexate Clinical Response in Portuguese Rheumatoid Arthritis Patients: Implication of MTHFR rs1801133 and ATIC rs4673993 Polymorphisms

PubMed Central

Lima, Aurea; Monteiro, Joaquim; Bernardes, Miguel; Sousa, Hugo; Azevedo, Rita; Seabra, Vitor; Medeiros, Rui

2014-01-01

Objective. Methotrexate (MTX), the most used drug in rheumatoid arthritis (RA) treatment, showing variability in clinical response, is often associated with genetic polymorphisms. This study aimed to elucidate the role of methylenetetrahydrofolate reductase (MTHFR) C677T and aminoimidazole carboxamide adenosine ribonucleotide transformylase (ATIC) T675C polymorphisms and clinicopathological variables in clinical response to MTX in Portuguese RA patients. Methods. Study included 233 RA patients treated with MTX for at least six months. MTHFR C677T and ATIC T675C polymorphisms were genotyped and clinicopathological variables were collected. Statistical analyses were performed and binary logistic regression method adjusted to possible confounding variables. Results. Multivariate analyses demonstrated that MTHFR 677TT (OR = 4.63; P = 0.013) and ATIC 675T carriers (OR = 5.16; P = 0.013) were associated with over 4-fold increased risk for nonresponse. For clinicopathological variables, noncurrent smokers (OR = 7.98; P = 0.001), patients positive to anti-cyclic citrullinated peptide (OR = 3.53; P = 0.004) and antinuclear antibodies (OR = 2.28; P = 0.045), with higher health assessment questionnaire score (OR = 2.42; P = 0.007), and nonsteroidal anti-inflammatory drug users (OR = 2.77; P = 0.018) were also associated with nonresponse. Contrarily, subcutaneous administration route (OR = 0.11; P < 0.001) was associated with response. Conclusion. Our study suggests that MTHFR C677T and ATIC T675C genotyping combined with clinicopathological data may help to identify patients whom will not benefit from MTX treatment and, therefore, assist clinicians in personalizing RA treatment. PMID:24967362

Longitudinal Monitoring of Patients With Chronic Low Back Pain During Physical Therapy Treatment Using the STarT Back Screening Tool.

PubMed

Medeiros, Flávia Cordeiro; Costa, Leonardo Oliveira Pena; Added, Marco Aurélio Nemitalla; Salomão, Evelyn Cassia; Costa, Lucíola da Cunha Menezes

2017-05-01

Study Design Preplanned secondary analysis of a randomized clinical trial. Background The STarT Back Screening Tool (SBST) was developed to screen and to classify patients with low back pain into subgroups for the risk of having a poor prognosis. However, this classification at baseline does not take into account variables that can influence the prognosis during treatment or over time. Objectives (1) To investigate the changes in risk subgroup measured by the SBST over a period of 6 months, and (2) to assess the long-term predictive ability of the SBST when administered at different time points. Methods Patients with chronic nonspecific low back pain (n = 148) receiving physical therapy care as part of a randomized trial were analyzed. Pain intensity, disability, global perceived effect, and the SBST were collected at baseline, 5 weeks, 3 months, and 6 months. Changes in SBST risk classification were calculated. Hierarchical linear regression models adjusted for potential confounders were built to analyze the predictive capabilities of the SBST when administered at different time points. Results A large proportion of patients (60.8%) changed their risk subgroup after receiving physical therapy care. The SBST improved the prediction for all 6-month outcomes when using the 5-week risk subgroup and the difference between baseline and 5-week subgroup, after controlling for potential confounders. The SBST at baseline did not improve the predictive ability of the models after adjusting for confounders. Conclusion This study shows that many patients change SBST risk subgroup after receiving physical therapy care, and that the predictive ability of the SBST in patients with chronic low back pain increases when administered at different time points. Level of Evidence Prognosis, 2b. J Orthop Sports Phys Ther 2017;47(5):314-323. Epub 29 Mar 2017. doi:10.2519/jospt.2017.7199.

Gender Consideration in Experiment Design for Airbrake in Prebreathe

NASA Technical Reports Server (NTRS)

Conkin, Johnny; Gernhardt, Michael I.; Dervay, Joseph P.

2007-01-01

If gender is a confounder of the decompression sickness (DCS) or venous gas emboli (VGE) outcomes of a proposed air break in oxygen prebreathe (PB) project, then decisions about the final experiment design must be made. We evaluated if the incidence of DCS and VGE from tests in altitude chambers over 20 years were different between men and women after resting and exercise prebreathe protocols. Nitrogen washout during PB is our primary risk mitigation strategy to prevent subsequent DCS and VGE in subjects. Bubbles in the pulmonary artery (venous blood) were detected from the precordial position using Doppler ultrasound bubble detectors. The subjects were monitored for VGE for four min at about 15 min intervals for the duration of the altitude exposure, with maximum bubble grade assigned a Spencer Grade of IV. There was no difference in DCS incidence between men and women in either PB protocol. The incidence of VGE and Grade IV VGE is statistically lower in women compared to men after resting PB. Even when 10 tests were compared with Mantel-Haenszel 2 where both men (n = 168) and women (n = 92) appeared, the p-value for VGE incidence was still significant at 0.03. The incidence of VGE and Grade IV VGE is not statistically lower in women compared to men after exercise PB. Even when six tests were compared with Mantel-Haenszel x2 where both men (n = 165) and women (n = 49) appeared, the p-value for VGE incidence was still not significant at 0.90. Our goal is to understand the risk of brief air breaks during PB without other confounding variables invalidating our conclusions. The cost to additionally account for the confounding role of gender on VGE outcome after resting PB is judged excessive. Our decision is to only evaluate air breaks in the exercise PB protocol. So there is no restriction to recruiting women as test subjects.

Do the wealthy have a health advantage? Cardiovascular disease risk factors and wealth.

PubMed

Hajat, A; Kaufman, J S; Rose, K M; Siddiqi, A; Thomas, J C

2010-12-01

The use of wealth as a measure of socioeconomic status (SES) remains uncommon in epidemiological studies. When used, wealth is often measured crudely and at a single point in time. Our study explores the relationship between wealth and three cardiovascular disease (CVD) risk factors (smoking, obesity and hypertension) in a US population. We improve upon existing literature by using a detailed and validated measure of wealth in a longitudinal setting. We used four waves of data from the Panel Study of Income Dynamics (PSID) collected between 1999 and 2005. Inverse probability weights were employed to control for time-varying confounding and to estimate both relative (risk ratio) and absolute (risk difference) measures of effect. Wealth was defined as inflation-adjusted net worth and specified as a six category variable: one category for those with less than or equal to zero wealth and quintiles of positive wealth. After adjusting for income and other time-varying confounders, as well as baseline covariates, the risk of becoming obese was inversely related to wealth. There was a 40%-89% higher risk of becoming obese among the less wealthy relative to the wealthiest quintile and 11 to 25 excess cases (per 1000 persons) among the less wealthy groups over six years of follow up. Smoking initiation had similar but more moderate effects; risk ratios and differences both revealed a smaller magnitude of effect compared to obesity. Of the three CVD risk factors examined here, hypertension incidence had the weakest association with wealth, showing a smaller increased risk and fewer excess cases among the less wealthy groups. In conclusion, this study found a strong inverse association between wealth and obesity incidence, a moderate inverse association between wealth and smoking initiation and a weak inverse association between wealth and hypertension incidence after controlling for income and other time-varying confounders. Copyright © 2010 Elsevier Ltd. All rights reserved.

The Well-Being of Siblings of Individuals with Autism

PubMed Central

Green, Laura

2013-01-01

Objective. The purpose of this review of the literature was to summarise studies regarding the psychosocial impact of growing up with a sibling with autism and to identify gaps in the related literature. Methods. Electronic databases were reviewed in order to critically appraise the 14 articles relevant to the topic. The search included a combination of the following key words: autism∗, quality of life, well-being, sibling∗, ASD, ASD sibling∗, family, adjust∗, psychological functioning. Results. The majority of studies involved mixed children and adolescent samples, leading to confounding results and an inability to draw accurate conclusions about these distinct life stages. Autism appears to contribute to unique environmental stressors for the typically developing sibling. When experienced in the context of additional demographic risk factors, these stressors can result in difficulties adjusting to the demands of a special-needs child. Despite some vulnerability to behavioural and emotional dysfunction in at-risk children, siblings have the potential to not only adjust but to thrive in the face of disability adversity. Conclusion. Growing up with a sibling with autism appears to manifest in both positive and negative outcomes for siblings, depending upon important demographical, family, and individual variables. PMID:23738144

Understanding logistic regression analysis.

PubMed

Sperandei, Sandro

2014-01-01

Logistic regression is used to obtain odds ratio in the presence of more than one explanatory variable. The procedure is quite similar to multiple linear regression, with the exception that the response variable is binomial. The result is the impact of each variable on the odds ratio of the observed event of interest. The main advantage is to avoid confounding effects by analyzing the association of all variables together. In this article, we explain the logistic regression procedure using examples to make it as simple as possible. After definition of the technique, the basic interpretation of the results is highlighted and then some special issues are discussed.

Intuitive Logic Revisited: New Data and a Bayesian Mixed Model Meta-Analysis

PubMed Central

Singmann, Henrik; Klauer, Karl Christoph; Kellen, David

2014-01-01

Recent research on syllogistic reasoning suggests that the logical status (valid vs. invalid) of even difficult syllogisms can be intuitively detected via differences in conceptual fluency between logically valid and invalid syllogisms when participants are asked to rate how much they like a conclusion following from a syllogism (Morsanyi & Handley, 2012). These claims of an intuitive logic are at odds with most theories on syllogistic reasoning which posit that detecting the logical status of difficult syllogisms requires effortful and deliberate cognitive processes. We present new data replicating the effects reported by Morsanyi and Handley, but show that this effect is eliminated when controlling for a possible confound in terms of conclusion content. Additionally, we reanalyze three studies () without this confound with a Bayesian mixed model meta-analysis (i.e., controlling for participant and item effects) which provides evidence for the null-hypothesis and against Morsanyi and Handley's claim. PMID:24755777

Assessing the independent contribution of maternal educational expectations to children's educational attainment in early adulthood: a propensity score matching analysis.

PubMed

Pingault, Jean Baptiste; Côté, Sylvana M; Petitclerc, Amélie; Vitaro, Frank; Tremblay, Richard E

2015-01-01

Parental educational expectations have been associated with children's educational attainment in a number of long-term longitudinal studies, but whether this relationship is causal has long been debated. The aims of this prospective study were twofold: 1) test whether low maternal educational expectations contributed to failure to graduate from high school; and 2) compare the results obtained using different strategies for accounting for confounding variables (i.e. multivariate regression and propensity score matching). The study sample included 1,279 participants from the Quebec Longitudinal Study of Kindergarten Children. Maternal educational expectations were assessed when the participants were aged 12 years. High school graduation—measuring educational attainment—was determined through the Quebec Ministry of Education when the participants were aged 22-23 years. Findings show that when using the most common statistical approach (i.e. multivariate regressions to adjust for a restricted set of potential confounders) the contribution of low maternal educational expectations to failure to graduate from high school was statistically significant. However, when using propensity score matching, the contribution of maternal expectations was reduced and remained statistically significant only for males. The results of this study are consistent with the possibility that the contribution of parental expectations to educational attainment is overestimated in the available literature. This may be explained by the use of a restricted range of potential confounding variables as well as the dearth of studies using appropriate statistical techniques and study designs in order to minimize confounding. Each of these techniques and designs, including propensity score matching, has its strengths and limitations: A more comprehensive understanding of the causal role of parental expectations will stem from a convergence of findings from studies using different techniques and designs.

A Bayesian Framework to Account for Complex Non-Genetic Factors in Gene Expression Levels Greatly Increases Power in eQTL Studies

PubMed Central

Durbin, Richard; Winn, John

2010-01-01

Gene expression measurements are influenced by a wide range of factors, such as the state of the cell, experimental conditions and variants in the sequence of regulatory regions. To understand the effect of a variable of interest, such as the genotype of a locus, it is important to account for variation that is due to confounding causes. Here, we present VBQTL, a probabilistic approach for mapping expression quantitative trait loci (eQTLs) that jointly models contributions from genotype as well as known and hidden confounding factors. VBQTL is implemented within an efficient and flexible inference framework, making it fast and tractable on large-scale problems. We compare the performance of VBQTL with alternative methods for dealing with confounding variability on eQTL mapping datasets from simulations, yeast, mouse, and human. Employing Bayesian complexity control and joint modelling is shown to result in more precise estimates of the contribution of different confounding factors resulting in additional associations to measured transcript levels compared to alternative approaches. We present a threefold larger collection of cis eQTLs than previously found in a whole-genome eQTL scan of an outbred human population. Altogether, 27% of the tested probes show a significant genetic association in cis, and we validate that the additional eQTLs are likely to be real by replicating them in different sets of individuals. Our method is the next step in the analysis of high-dimensional phenotype data, and its application has revealed insights into genetic regulation of gene expression by demonstrating more abundant cis-acting eQTLs in human than previously shown. Our software is freely available online at http://www.sanger.ac.uk/resources/software/peer/. PMID:20463871

Association between age associated cognitive decline and health related quality of life among Iranian older individuals.

PubMed

Kazazi, Leila; Foroughan, Mahshid; Nejati, Vahid; Shati, Mohsen

2018-04-01

Age associated cognitive decline or normal cognitive aging is related with lower levels of functioning in real life, and may interfere with maintaining independence and health related quality of life (HRQL). In this study, health related quality of life and cognitive function in community-dwelling older adults were evaluated with the aim of exploring the association between them by adjusting for potential confounders. This cross-sectional study, was implemented on 425 community-dwelling older adults aged 60 and over, between August 2016 and October 2016 in health centers of the municipality of Tehran, Iran, using Mini Mental State Examination (MMSE) to assess cognitive function and Short Form-36 scales (SF-36) to assess HRQL. The relation between HRQL and cognitive function was evaluated by Pearson's correlation coefficient, and the impact of cognitive function on HRQL adjusted for potential confounders was estimated by linear regression model. All analyses were done using SPSS, version 22.0. A positive significant correlation between cognitive function and quality of life (r=0.434; p<0.001) and its dimensions was observed. Two variables of educational level (B=2.704; 95% CI: 2.09 to 3.30; p<0.001) and depression (B=2.554; 95% CI: 2.00 to 3.10; p<0.001) were assumed as potential confounder by changing effect measure after entering the model. After adjusting for potential confounders in regression model, the association between MMSE scores and quality of life persisted (B=2.417; 95% CI: 1.86 to 2.96; p<0.001). The results indicate that cognitive function was associated with HRQL in older adults with age associated cognitive function. Two variables of educational level and depression can affect the relation between cognitive decline and HRQL.

The relationship of bone and blood lead to hypertension: Further analyses of the normative aging study data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, H.; Kim, Rokho; Korrick, S.

1996-12-31

In an earlier report based on participants in the Veterans Administration Normative Aging Study, we found a significant association between the risk of hypertension and lead levels in tibia. To examine the possible confounding effects of education and occupation, we considered in this study five levels of education and three levels of occupation as independent variables in the statistical model. Of 1,171 active subjects seen between August 1991 and December 1994, 563 provided complete data for this analysis. In the initial logistic regression model, acre and body mass index, family history of hypertension, and dietary sodium intake, but neither cumulativemore » smoking nor alcohol ingestion, conferred increased odds ratios for being hypertensive that were statistically significant. When the lead biomarkers were added separately to this initial logistic model, tibia lead and patella lead levels were associated with significantly elevated odds ratios for hypertension. In the final backward elimination logistic regression model that included categorical variables for education and occupation, the only variables retained were body mass index, family history of hypertension, and tibia lead level. We conclude that education and occupation variables were not confounding the association between the lead biomarkers and hypertension that we reported previously. 27 refs., 3 tabs.« less

Spinal Cord Injury and Migraine Headache: A Population-Based Study

PubMed Central

Warner, Freda M.; Cragg, Jacquelyn J.; Weisskopf, Marc G.; Kramer, John K.

2015-01-01

Migraine headaches are a common neurological condition, negatively impacting health and quality of life. Among potential risk factors for migraine headache, risk of migraine headaches was elevated in individuals with spinal cord injury (SCI). The association between migraines and SCI is intriguing to consider from the perspective that migraine headaches may be acquired in response to damage in the spinal cord. The primary objective of this study was to further examine the association between SCI and migraine headache, controlling for potential confounding variables. A secondary objective was to determine the impact of migraine headaches on self-perceived health. Data from a sample of 61,047 participants were obtained from the cross-sectional Canadian Community Health Survey. Multivariable logistic regression was used to explore the association between SCI and migraine headache using probability weights and adjusting for confounders. The multivariable age- and sex-adjusted model revealed a strong association between SCI and migraine headache, with an adjusted odds ratio for migraine of 4.82 (95% confidence interval [3.02, 7.67]) among those with SCI compared to those without SCI. Further, individuals who experienced both SCI and migraine tended to report poorer perceived general health compared with the other groups (i.e., SCI and no migraine). In conclusion, this study established a strong association between SCI and migraine headache. Further research is needed to explore the possible mechanisms underlying this relationship. Improvements in clinical practice to minimize this issue could result in significant improvements in quality of life. PMID:26308549

Oxytocin in the Treatment of Dystocia in Mice

PubMed Central

Narver, Heather L

2012-01-01

Physicians and veterinarians often prescribe oxytocin to treat dystocia. However, oxytocin administration to pregnant women or animals is not without risk. In the venue of laboratory animal medicine, the use of oxytocin may present confounding variables to research. Although oxytocin has been studied extensively, many of its physiologic effects and interactions with other hormones remain unclear. Investigator concerns about adverse and confounding effects of oxytocin in their research mice prompted the current review of oxytocin and its use to treat murine dystocia. Well-controlled studies of oxytocin in dystocic mice have not been conducted. However, in humans and other animals, inconsistent and adverse effects are well-documented. Limited knowledge of the complex physiologic and molecular mechanisms of action of oxytocin and scant support for the efficacy of oxytocin in dystocic mice fail to meet the standards of evidence-based veterinary medical practice. The administration of oxytocin is contraindicated in many cases of dystocia in research mice, and its use in dystocic mice may be unfounded. A brief review of oxytocin and the physiologic mechanisms of parturition are provided to support this conclusion. Alternative treatments for murine dystocia are discussed, and a holistic approach is advocated to better serve animal welfare and to safeguard the integrity of valuable research. Laboratory animal veterinarians overseeing the development of guidelines or standard operating procedures for technician or investigator treatment of dystocic mice should understand the effects of oxytocin administration in light of relevant research. PMID:22330862

Track and Field Practice and Bone Outcomes among Adolescents: A Pilot Study (ABCD-Growth Study)

PubMed Central

Faustino-da-Silva, Yuri da Silva Ventura; Werneck, André Oliveira; Maillane-Vanegas, Santiago; Lynch, Kyle Robinson; Exupério, Isabella Neto; Ito, Igor Hideki; Fernandes, Romulo Araújo

2018-01-01

Background Osteoporosis is considered a public health problem with high worldwide prevalence. One approach to prevention is through the promotion of physical activity, especially exercise, during adolescence. Methods This study compared bone variables in different body segments in adolescents according to participation in track and field. The study included 34 adolescents (22 boys), of whom 17 were track and field athletes and 17 were control subjects. Bone mineral density (BMD, g/cm2) and bone mineral content (BMC, g) were analyzed using dual energy X-ray absorptiometry (total body stratified by body segments). Peak height velocity was used to estimate somatic maturation. Results Athletes had higher BMD (P=0.003) and BMC (P=0.011) values in the lower limbs and higher whole body BMD (P=0.025) than the control group. However, when adjusted for confounding factors, the difference was not maintained. The groups had similar lean soft tissue values (P=0.094). Training overload was positively correlated with BMD in the upper limbs (r=0.504; 95% confidence interval, 0.031-0.793). Although track and field athletes had higher BMD and BMC values in the lower limbs, these differences were not significant when adjusted for confounding factors. Conclusions Track and field participation in adolescence appears to influence BMD and BMC in lower limbs, and fat-free mass seems to mediate this effect. Also, higher training loads were found to be positive for bone health in upper limbs. PMID:29564304

The effects of socioeconomic status and indices of physical environment on reduced birth weight and preterm births in Eastern Massachusetts

PubMed Central

Zeka, Ariana; Melly, Steve J; Schwartz, Joel

2008-01-01

Background Air pollution and social characteristics have been shown to affect indicators of health. While use of spatial methods to estimate exposure to air pollution has increased the power to detect effects, questions have been raised about potential for confounding by social factors. Methods A study of singleton births in Eastern Massachusetts was conducted between 1996 and 2002 to examine the association between indicators of traffic, land use, individual and area-based socioeconomic measures (SEM), and birth outcomes (birth weight, small for gestational age and preterm births), in a two-level hierarchical model. Results We found effects of both individual (education, race, prenatal care index) and area-based (median household income) SEM with all birth outcomes. The associations for traffic and land use variables were mainly seen with birth weight, with an exception for an effect of cumulative traffic density on small for gestational age. Race/ethnicity of mother was an important predictor of birth outcomes and a strong confounder for both area-based SEM and indices of physical environment. The effects of traffic and land use differed by level of education and median household income. Conclusion Overall, the findings of the study suggested greater likelihood of reduced birth weight and preterm births among the more socially disadvantaged, and a greater risk of reduced birth weight associated with traffic exposures. Results revealed the importance of controlling simultaneously for SEM and environmental exposures as the way to better understand determinants of health. PMID:19032747

Language Outcomes at 12 Years for Children Exposed Prenatally to Cocaine

PubMed Central

Lewis, Barbara A.; Minnes, Sonia; Short, Elizabeth J.; Min, Meeyoung O.; Wu, Miaoping; Lang, Adelaide; Weishampel, Paul; Singer, Lynn T.

2014-01-01

Purpose In this study, the authors aimed to examine the long-term effects of prenatal cocaine exposure (PCE) on the language development of 12-year-old children using a prospective design, controlling for confounding prenatal drug exposure and environmental factors. Method Children who were exposed to cocaine in utero (PCE; n = 183) and children who were not exposed to cocaine (i.e., no cocaine exposure [NCE]; n = 181) were followed prospectively from birth to 12 years of age and were compared on language subtests of the Test of Language Development—Intermediate, Third Edition (Hammill & Newcomer, 1997b), and phonological processing as measured by the Comprehensive Test of Phonological Processing (Wagner & Torgesen, 1999). The authors evaluated the relationship of PCE to language development through a multivariate analysis of covariance and regression analyses while controlling for confounders. Results Results show that PCE has small effects on specific aspects of language, including syntax and phonological processing. The caregiver variables of lower maternal vocabulary, more psychological symptoms, and a poorer home environment also had consistent effects on language and phonological processing scores. Conclusions These findings suggest that PCE continues to have small, subtle effects on specific aspects of language at age 12 years. Phonological processing skills were significantly related to the reading outcomes of letter–word identification, reading fluency, and reading comprehension, indicating that PCE also has small but lasting effects on the language skills that are related to later literacy skills. PMID:24149136

Association Between Zolpidem Use and Glaucoma Risk: A Taiwanese Population-Based Case-Control Study

PubMed Central

Ho, Yi-Hao; Chang, Yue-Cune; Huang, Wei-Cheng; Chen, Hsin-Yi; Lin, Che-Chen; Sung, Fung-Chang

2015-01-01

Background To date, the relationship between zolpidem use and subsequent risk of glaucoma in a Taiwanese population has not been assessed. Methods We used data from the National Health Insurance system to investigate whether zolpidem use was related to glaucoma risk. A 1:4 matched case-control study was conducted. The cases were patients newly diagnosed with glaucoma from 2001 to 2010. The controls were randomly selected non-glaucoma subjects matched by sex and age (±5 years). Zolpidem exposure and/or the average dosage of zolpidem used (mg/year) were evaluated. Medical comorbidities were considered as confounding factors. Multiple logistic regression models were used to evaluate the potential risk of zolpidem exposure on glaucoma with/without adjustment for the effects of confounding variables. Results The exposure rate of zolpidem use in the glaucoma group was significantly higher than that of the control group (2.8% vs. 2.0%, P < 0.0001). The adjusted odds ratio (OR) of the risk of glaucoma for those with zolpidem use vs. those without was 1.19 (95% confidence interval [CI], 1.02–1.38). Compared to non-zolpidem users, zolpidem users with an average dose of more than 200 mg/year had significantly increased risk of glaucoma (OR 1.31, 95% CI 1.03–1.68). Conclusions This study suggests that the use of zolpidem might increase the risk of subsequent glaucoma. Further confirmatory studies are recommended to clarify this important issue. PMID:25720944

Association Between Zolpidem Use and Glaucoma Risk: A Taiwanese Population-Based Case-Control Study.

PubMed

Ho, Yi-Hao; Chang, Yue-Cune; Huang, Wei-Cheng; Chen, Hsin-Yi; Lin, Che-Chen; Sung, Fung-Chang

2014-08-23

Background: To date, the relationship between zolpidem use and subsequent risk of glaucoma in a Taiwanese population has not been assessed.Methods: We used data from the National Health Insurance system to investigate whether zolpidem use was related to glaucoma risk. A 1:4 matched case-control study was conducted. The cases were patients newly diagnosed with glaucoma from 2001 to 2010. The controls were randomly selected non-glaucoma subjects matched by sex and age (±5 years). Zolpidem exposure and/or the average dosage of zolpidem used (mg/year) were evaluated. Medical comorbidities were considered as confounding factors. Multiple logistic regression models were used to evaluate the potential risk of zolpidem exposure on glaucoma with/without adjustment for the effects of confounding variables.Results: The exposure rate of zolpidem use in the glaucoma group was significantly higher than that of the control group (2.8% vs. 2.0%, P < 0.0001). The adjusted odds ratio (OR) of the risk of glaucoma for those with zolpidem use vs. those without was 1.19 (95% confidence interval [CI], 1.02-1.38). Compared to non-zolpidem users, zolpidem users with an average dose of more than 200 mg/year had significantly increased risk of glaucoma (OR 1.31, 95% CI 1.03-1.68).Conclusions: This study suggests that the use of zolpidem might increase the risk of subsequent glaucoma. Further confirmatory studies are recommended to clarify this important issue.

Inter-Hospital Transfer is Associated with Increased Mortality and Costs in Severe Sepsis and Septic Shock: An Instrumental Variables Approach

PubMed Central

Mohr, Nicholas M.; Harland, Karisa K.; Shane, Dan M.; Ahmed, Azeemuddin; Fuller, Brian M.; Torner, James C.

2016-01-01

Purpose The objective of this study was to evaluate the impact of regionalization on sepsis survival, to describe the role of inter-hospital transfer in rural sepsis care, and to measure the cost of inter-hospital transfer in a predominantly rural state. Materials and Methods Observational case-control study using statewide administrative claims data from 2005-2014 in a predominantly rural Midwestern state. Mortality and marginal costs were estimated with multivariable generalized estimating equations (GEE) models and with instrumental variables models. Results A total of 18,246 patients were included, of which 59% were transferred between hospitals. Transferred patients had higher mortality and longer hospital length-of-stay than non-transferred patients. Using a multivariable GEE model to adjust for potentially confounding factors, inter-hospital transfer was associated with increased mortality (aOR 1.7, 95%CI 1.5 – 1.9). Using an instrumental variables model, transfer was associated with a 9.2% increased risk of death. Transfer was associated with additional costs of $6,897 (95%CI $5,769-8,024). Even when limiting to only those patients who received care in the largest hospitals, transfer was still associated with $5,167 (95%CI $3,696-6,638) in additional cost. Conclusions The majority of rural sepsis patients are transferred, and these transferred patients have higher mortality and significantly increased cost of care. PMID:27546770

Association of quality of life and job stress in occupational workforce of India: Findings from a cross-sectional study on software professionals

PubMed Central

Babu, Giridhara R.; Sudhir, Paulomi M.; Mahapatra, Tanmay; Das, Aritra; Rathnaiah, Mohanbabu; Anand, Indiresh; Detels, Roger

2016-01-01

Background: There is limited scientific evidence on the relationship of job stress with quality of life (QoL). Purpose: This study aims to explore different domains of job stress affecting IT/ITES professionals and estimate the levels of stress that these professionals endure to reach positive levels of QoL given that other determinants operating between these two variables are accounted for. Materials and Methods: We estimated levels of stress that software professionals would have endured to reach positive levels of QoL considering that other factors operating between these two variables are accounted for. The study participants comprised 1071 software professionals who were recruited using a mixed sampling method. Participants answered a self-administered questionnaire containing questions on job stress, QoL, and confounders. Results: All the domains (physical, psychological, social, and environmental) of QoL showed statistically significant positive associations with increasing stress domains of autonomy, physical infrastructure, work environment, and emotional factors. Conclusions: The respondents clearly found the trade-off of higher stress to be acceptable for the improved QoL they enjoyed. It is also possible that stress might actually be responsible for improvements in QoL either directly or through mediation of variables such as personal values and aspirations. Yerkes-Dodson law and stress appraisal models of Folkman and Lazarus may explain the plausible positive association. PMID:28194085

An evaluation of exact matching and propensity score methods as applied in a comparative effectiveness study of inhaled corticosteroids in asthma

PubMed Central

Burden, Anne; Roche, Nicolas; Miglio, Cristiana; Hillyer, Elizabeth V; Postma, Dirkje S; Herings, Ron MC; Overbeek, Jetty A; Khalid, Javaria Mona; van Eickels, Daniela; Price, David B

2017-01-01

Background Cohort matching and regression modeling are used in observational studies to control for confounding factors when estimating treatment effects. Our objective was to evaluate exact matching and propensity score methods by applying them in a 1-year pre–post historical database study to investigate asthma-related outcomes by treatment. Methods We drew on longitudinal medical record data in the PHARMO database for asthma patients prescribed the treatments to be compared (ciclesonide and fine-particle inhaled corticosteroid [ICS]). Propensity score methods that we evaluated were propensity score matching (PSM) using two different algorithms, the inverse probability of treatment weighting (IPTW), covariate adjustment using the propensity score, and propensity score stratification. We defined balance, using standardized differences, as differences of <10% between cohorts. Results Of 4064 eligible patients, 1382 (34%) were prescribed ciclesonide and 2682 (66%) fine-particle ICS. The IPTW and propensity score-based methods retained more patients (96%–100%) than exact matching (90%); exact matching selected less severe patients. Standardized differences were >10% for four variables in the exact-matched dataset and <10% for both PSM algorithms and the weighted pseudo-dataset used in the IPTW method. With all methods, ciclesonide was associated with better 1-year asthma-related outcomes, at one-third the prescribed dose, than fine-particle ICS; results varied slightly by method, but direction and statistical significance remained the same. Conclusion We found that each method has its particular strengths, and we recommend at least two methods be applied for each matched cohort study to evaluate the robustness of the findings. Balance diagnostics should be applied with all methods to check the balance of confounders between treatment cohorts. If exact matching is used, the calculation of a propensity score could be useful to identify variables that require balancing, thereby informing the choice of matching criteria together with clinical considerations. PMID:28356782

Comparison of clipping and coiling in elderly patients with unruptured cerebral aneurysms

PubMed Central

Bekelis, Kimon; Gottlieb, Daniel J.; Su, Yin; O’Malley, A. James; Labropoulos, Nicos; Goodney, Philip; Lawton, Michael T.; MacKenzie, Todd A.

2016-01-01

OBJECTIVE The comparative effectiveness of the 2 treatment options—surgical clipping and endovascular coiling—for unruptured cerebral aneurysms remains an issue of debate and has not been studied in clinical trials. The authors investigated the association between treatment method for unruptured cerebral aneurysms and outcomes in elderly patients. METHODS The authors performed a cohort study of 100% of Medicare fee-for-service claims data for elderly patients who had treatment for unruptured cerebral aneurysms between 2007 and 2012. To control for measured confounding, the authors used propensity score conditioning and inverse probability weighting with mixed effects to account for clustering at the level of the hospital referral region (HRR). An instrumental variable (regional rates of coiling) analysis was used to control for unmeasured confounding and to create pseudo-randomization on the treatment method. RESULTS During the study period, 8705 patients underwent treatment for unruptured cerebral aneurysms and met the study inclusion criteria. Of these patients, 2585 (29.7%) had surgical clipping and 6120 (70.3%) had endovascular coiling. Instrumental variable analysis demonstrated no difference between coiling and clipping in 1-year postoperative mortality (OR 1.25, 95% CI 0.68–2.31) or 90-day readmission rate (OR 1.04, 95% CI 0.66–1.62). However, clipping was associated with a greater likelihood of discharge to rehabilitation (OR 6.39, 95% CI 3.85–10.59) and 3.6 days longer length of stay (LOS; 95% CI 2.90–4.71). The same associations were present in propensity score–adjusted and inverse probability– weighted models. CONCLUSIONS In a cohort of Medicare patients, there was no difference in mortality and the readmission rate between clipping and coiling of unruptured cerebral aneurysms. Clipping was associated with a higher rate of discharge to a rehabilitation facility and a longer LOS. PMID:27203150

First report on body image and weight control in a nationally representative sample of a pediatric population in the Middle East and North Africa: the CASPIAN-III study

PubMed Central

Marashinia, Farzad; Heshmat, Ramin; Motlagh, Mohammad-Esmaeil; Qorbani, Mostafa; Taslimi, Mahnaz; Nourbakhsh, Mohsen; Ardalan, Gelayol; Poursafa, Parinaz

2013-01-01

Introduction This study explores the associations of weight perceptions with actual body mass index (BMI) and attempts to lose weight in a nationally representative sample of a pediatric population. Material and methods Data were collected from school students of 27 provinces in Iran, as part of “the national survey of school student high risk behaviors”. We used t-test for continuous data and chi square test for categorical data. The correlation between categorical variables was assessed by Cramer's phi test. A multiple nominal logistic regression model was fitted to data to assess the association between perceived body weight and gender by adjusting for potential confounding variables. Results The study participants consisted of 5570 (2784 girls, 70% urban) students with mean age of 14.7 ±2.4 years. Overall, 17.3% of students were underweight, and 17.7% were overweight or obese. Nearly 25% and 50% of participants reported themselves as appropriate weight and very obese, respectively. In both genders, the strength of association between perceived weight and actual BMI was quite high (Cramer's phi coefficient = 0.5, p < 0.0001), and that of perceived body weight with trying to lose weight was moderate (Cramer's phi coefficient = 0.2, p < 0.0001). Overweight students were more likely than their obese peers to try to lose weight. After adjusting for possible confounders, the chance of perceiving oneself as very obese compared to perceiving oneself as very thin was 1.56-fold higher in girls than in boys, i.e. OR (95% CI): 1.56 (1.27-1.91). Conclusions This study revealed a considerably frequent “mismatch” between actual weight status and body shape dissatisfaction, which supports the necessity of increasing public awareness in this regard. PMID:23671430

Mortality rates at 10 years after metal-on-metal hip resurfacing compared with total hip replacement in England: retrospective cohort analysis of hospital episode statistics

PubMed Central

Kendal, Adrian R; Prieto-Alhambra, Daniel; Arden, Nigel K; Judge, Andrew

2013-01-01

Objectives To compare 10 year mortality rates among patients undergoing metal-on-metal hip resurfacing and total hip replacement in England. Design Retrospective cohort study. Setting English hospital episode statistics database linked to mortality records from the Office for National Statistics. Population All adults who underwent primary elective hip replacement for osteoarthritis from April 1999 to March 2012. The exposure of interest was prosthesis type: cemented total hip replacement, uncemented total hip replacement, and metal-on-metal hip resurfacing. Confounding variables included age, sex, Charlson comorbidity index, rurality, area deprivation, surgical volume, and year of operation. Main outcome measures All cause mortality. Propensity score matching was used to minimise confounding by indication. Kaplan-Meier plots estimated the probability of survival up to 10 years after surgery. Multilevel Cox regression modelling, stratified on matched sets, described the association between prosthesis type and time to death, accounting for variation across hospital trusts. Results 7437 patients undergoing metal-on-metal hip resurfacing were matched to 22 311 undergoing cemented total hip replacement; 8101 patients undergoing metal-on-metal hip resurfacing were matched to 24 303 undergoing uncemented total hip replacement. 10 year rates of cumulative mortality were 271 (3.6%) for metal-on-metal hip resurfacing versus 1363 (6.1%) for cemented total hip replacement, and 239 (3.0%) for metal-on-metal hip resurfacing versus 999 (4.1%) for uncemented total hip replacement. Patients undergoing metal-on-metal hip resurfacing had an increased survival probability (hazard ratio 0.51 (95% confidence interval 0.45 to 0.59) for cemented hip replacement; 0.55 (0.47 to 0.65) for uncemented hip replacement). There was no evidence for an interaction with age or sex. Conclusions Patients with hip osteoarthritis undergoing metal-on-metal hip resurfacing have reduced mortality in the long term compared with those undergoing cemented or uncemented total hip replacement. This difference persisted after extensive adjustment for confounding factors available in our data. The study results can be applied to matched populations, which exclude patients who are very old and have had complex total hip replacements. Although residual confounding is possible, the observed effect size is large. These findings require validation in external cohorts and randomised clinical trials. PMID:24284336

Does long-term care use within primary health care reduce hospital use among older people in Norway? A national five-year population-based observational study

PubMed Central

2011-01-01

Background Population ageing may threaten the sustainability of future health care systems. Strengthening primary health care, including long-term care, is one of several measures being taken to handle future health care needs and budgets. There is limited and inconsistent evidence on the effect of long-term care on hospital use. We explored the relationship between the total use of long-term care within public primary health care in Norway and the use of hospital beds when adjusting for various effect modifiers and confounders. Methods This national population-based observational study consists of all Norwegians (59% women) older than 66 years (N = 605676) (13.2% of total population) in 2002-2006. The unit of analysis was defined by municipality, age and sex. The association between total number of recipients of long-term care per 1000 inhabitants (LTC-rate) and hospital days per 1000 inhabitants (HD-rate) was analysed in a linear regression model. Modifying and confounding effects of socioeconomic, demographic and geographic variables were included in the final model. We defined a difference in hospitalization rates of more than 1000 days per 1000 inhabitants as clinically important. Results Thirty-one percent of women and eighteen percent of men were long-term care users. Men had higher HD-rates than women. The crude association between LTC-rate and HD-rate was weakly negative. We identified two effect modifiers (age and sex) and two strong confounders (travel time to hospital and mortality). Age and sex stratification and adjustments for confounders revealed a positive statistically significant but not clinically important relationship between LTC-rates and hospitalization for women aged 67-79 years and all men. For women 80 years and over there was a weak but negative relationship which was neither statistically significant nor clinically important. Conclusions We found a weak positive adjusted association between LTC-rates and HD-rates. Opposite to common belief, we found that increased volume of LTC by itself did not reduce pressure on hospitals. There still is a need to study integrated care models for the elderly in the Norwegian setting and to explore further why municipalities far away from hospital achieve lower use of hospital beds. PMID:22029775

COMPOSITE SAMPLING FOR SOIL VOC ANALYSIS

EPA Science Inventory

Data published by numerous researchers over the last decade demonstrate that there is a high degree of spatial variability in the measurement of volatile organic compounds (VOCs) in soil at contaminated waste sites. This phenomenon is confounded by the use of a small sample aliqu...

Childhood Medical and Behavioral Consequences of Maternal Cocaine Use1

PubMed Central

Singer, Lynn; Farkas, Kathleen; Kliegman, Robert

2014-01-01

Reviewed available studies of the impact of fetal cocaine exposure on child medical and developmental outcome, as well as the current status of clinical psychological interventions and research strategies. Current studies are inconclusive but suggest that prenatal exposure to crack-cocaine can have significant effects on the growth and neurological development of the infant, with the potential of later learning and behavioral disabilities. Social-environmental correlates of maternal cocaine use are confounding factors with known negative effects on child outcome. Large, population-based studies using multivariate analyses are needed to determine the independent effects of cocaine on child outcome relative to other confounding variables. PMID:1382125

The assessment of cortisol in human hair: associations with sociodemographic variables and potential confounders.

PubMed

Dettenborn, L; Tietze, A; Kirschbaum, C; Stalder, T

2012-11-01

To inform the future use of hair cortisol measurement, we have investigated influences of potential confounding variables (natural hair colour, frequency of hair washes, age, sex, oral contraceptive (OC) use and smoking status) on hair cortisol levels. The main study sample comprised 360 participants (172 women) covering a wide range of ages (1-91 years; mean = 25.95). In addition, to more closely examine influences of natural hair colour and young age on hair cortisol levels, two additional samples comprising 69 participants with natural blond or dark brown hair (hair colour sample) as well as 28 young children and 34 adults (young age sample) were recruited. Results revealed a lack of an effect for natural hair colour, OC use, and smoking status on hair cortisol levels (all p's >0.10). No influence of frequency of hair washes was seen for proximal hair segments (p = 0.335) but for the third hair segment indicating lower cortisol content (p = 0.008). We found elevated hair cortisol levels in young children and older adults (p < 0.001). Finally, men showed higher hair cortisol levels than women (p = 0.002). The present data indicate that hair cortisol measurement provides a useful tool in stress-related psychobiological research when applied with the consideration of possible confounders including age and sex.

Alcohol Use in Adolescence and Later Working Memory: Findings From a Large Population-Based Birth Cohort.

PubMed

Mahedy, Liam; Field, Matt; Gage, Suzanne; Hammerton, Gemma; Heron, Jon; Hickman, Matt; Munafò, Marcus R

2018-05-01

The study aimed to examine the association between adolescent alcohol use and working memory (WM) using a large population sample. Data from the Avon Longitudinal Study of Parents and Children were used to investigate the association between alcohol use at age 15 years and WM 3 years later, assessed using the N-back task (N ~ 3300). A three-category ordinal variable captured mutually exclusive alcohol groupings ranging in order of severity (i.e. low alcohol users, frequent drinkers and frequent/binge drinkers). Differential dropout was accounted for using multiple imputation and inverse probability weighting. Adjustment was made for potential confounders. There was evidence of an association between frequent/binge drinking (compared to the low alcohol group) and poorer performance on the 3-back task after adjusting for sociodemographic confounding variables, WM at age 11 years, and experience of a head injury/unconsciousness before age 11 years (β = -0.23, 95% CI = -0.37 to -0.09, P = 0.001). However, this association was attenuated (β = -0.12, 95% CI = -0.27 to 0.03, P = 0.11) when further adjusted for baseline measures of weekly cigarette tobacco and cannabis use. Weaker associations were found for the less demanding 2-back task. We found no evidence to suggest frequent drinking was associated with performance on either task. We found weak evidence of an association between sustained heavy alcohol use in mid-adolescence and impaired WM 3 years later. Although we cannot fully rule out the possibility of reverse causation, several potential confounding variables were included to address the directionality of the relationship between WM and alcohol use problems.

Pregnant women with the sickle cell trait are not at increased risk for developing preeclampsia.

PubMed

Stamilio, David M; Sehdev, Harish M; Macones, George A

2003-01-01

The primary objective of this study was to determine whether having the sickle cell trait is independently associated with preeclampsia. We performed a retrospective cohort study of 1998 pregnant patients who either did or did not have the sickle cell trait. All patients were screened for the sickle trait using the "Sickledex" test. Data on neonatal and maternal outcome, including preeclampsia, and potential confounding variables were abstracted from medical records. Unadjusted, stratified, and multiple logistic regression analyses were used to identify interactions, and confounding between multiple variables and the association between sickle cell trait and preeclampsia. With an anticipated 6.5% rate of preeclampsia, and alpha = 0.05, this cohort study has 80% power to detect a relative risk (RR) of 2.3 for preeclampsia. Univariate analysis revealed that the two cohorts were similar with regard to primiparity, maternal age, chronic diseases, birth weight, and gestational age at delivery, but the sickle cell trait cohort was more likely to have gestational diabetes and had a higher mean body mass index (BMI). In the univariate analysis, the sickle cell trait cohort was not at increased risk for preeclampsia [unadjusted RR = 0.5, 95% CI (0.2-1.6)]. After controlling for potential confounding variables with logistic regression analysis, sickle trait was not independently associated with preeclampsia [adjusted RR = 0.5, 95% CI (0.2- 1.6)]. In contrast to prior work, these data suggest that the sickle cell trait is not an independent risk factor for preeclampsia or postpartum complications. In fact, the data are more consistent with the sickle trait being protective for developing preeclampsia.

College quality and hourly wages: evidence from the self-revelation model, sibling models and instrumental variables.

PubMed

Borgen, Nicolai T

2014-11-01

This paper addresses the recent discussion on confounding in the returns to college quality literature using the Norwegian case. The main advantage of studying Norway is the quality of the data. Norwegian administrative data provide information on college applications, family relations and a rich set of control variables for all Norwegian citizens applying to college between 1997 and 2004 (N = 141,319) and their succeeding wages between 2003 and 2010 (676,079 person-year observations). With these data, this paper uses a subset of the models that have rendered mixed findings in the literature in order to investigate to what extent confounding biases the returns to college quality. I compare estimates obtained using standard regression models to estimates obtained using the self-revelation model of Dale and Krueger (2002), a sibling fixed effects model and the instrumental variable model used by Long (2008). Using these methods, I consistently find increasing returns to college quality over the course of students' work careers, with positive returns only later in students' work careers. I conclude that the standard regression estimate provides a reasonable estimate of the returns to college quality. Copyright © 2014 Elsevier Inc. All rights reserved.

Detectability and Interpretational Uncertainties: Considerations in Gauging the Impacts of Land Disturbance on Streamflow

EPA Science Inventory

Hydrologic impacts of land disturbance and management can be confounded by rainfall variability. As a consequence, attempts to gauge and quantify these effects through streamflow monitoring are typically subject to uncertainties. This paper addresses the quantification and deline...

Supportive Family Environments Ameliorate the Link Between Racial Discrimination and Epigenetic Aging: A Replication Across Two Longitudinal Cohorts.

PubMed

Brody, Gene H; Miller, Gregory E; Yu, Tianyi; Beach, Steven R H; Chen, Edith

2016-04-01

This study tested the hypothesis that supportive family environments during adolescence buffer exposure to racial discrimination, reducing its impact on biological weathering and its manifestation in cellular aging. Perceived racial discrimination, support in the family environment, and confounder variables were assessed for 3 consecutive years across adolescence in two independent cohorts of African American youth from rural Georgia. DNA was extracted from peripheral blood mononuclear cells collected during young adulthood. Patterns of methylation were used to index the epigenetic ages of these cells and the extent to which they differed from participants' chronological ages. Among youth in supportive family environments, exposure to higher levels of racial discrimination did not forecast greater epigenetic aging. Among youth in less supportive family environments, exposure to higher levels of racial discrimination did forecast greater epigenetic aging. The associations emerged independently of confounder variables, and the results were replicated across the two cohorts. © The Author(s) 2016.

Instrumental variable methods in comparative safety and effectiveness research†

PubMed Central

Brookhart, M. Alan; Rassen, Jeremy A.; Schneeweiss, Sebastian

2010-01-01

Summary Instrumental variable (IV) methods have been proposed as a potential approach to the common problem of uncontrolled confounding in comparative studies of medical interventions, but IV methods are unfamiliar to many researchers. The goal of this article is to provide a non-technical, practical introduction to IV methods for comparative safety and effectiveness research. We outline the principles and basic assumptions necessary for valid IV estimation, discuss how to interpret the results of an IV study, provide a review of instruments that have been used in comparative effectiveness research, and suggest some minimal reporting standards for an IV analysis. Finally, we offer our perspective of the role of IV estimation vis-à-vis more traditional approaches based on statistical modeling of the exposure or outcome. We anticipate that IV methods will be often underpowered for drug safety studies of very rare outcomes, but may be potentially useful in studies of intended effects where uncontrolled confounding may be substantial. PMID:20354968

Beyond logistic regression: structural equations modelling for binary variables and its application to investigating unobserved confounders.

PubMed

Kupek, Emil

2006-03-15

Structural equation modelling (SEM) has been increasingly used in medical statistics for solving a system of related regression equations. However, a great obstacle for its wider use has been its difficulty in handling categorical variables within the framework of generalised linear models. A large data set with a known structure among two related outcomes and three independent variables was generated to investigate the use of Yule's transformation of odds ratio (OR) into Q-metric by (OR-1)/(OR+1) to approximate Pearson's correlation coefficients between binary variables whose covariance structure can be further analysed by SEM. Percent of correctly classified events and non-events was compared with the classification obtained by logistic regression. The performance of SEM based on Q-metric was also checked on a small (N = 100) random sample of the data generated and on a real data set. SEM successfully recovered the generated model structure. SEM of real data suggested a significant influence of a latent confounding variable which would have not been detectable by standard logistic regression. SEM classification performance was broadly similar to that of the logistic regression. The analysis of binary data can be greatly enhanced by Yule's transformation of odds ratios into estimated correlation matrix that can be further analysed by SEM. The interpretation of results is aided by expressing them as odds ratios which are the most frequently used measure of effect in medical statistics.

Job Strain and the Cortisol Diurnal Cycle in MESA: Accounting for Between- and Within-Day Variability.

PubMed

Rudolph, Kara E; Sánchez, Brisa N; Stuart, Elizabeth A; Greenberg, Benjamin; Fujishiro, Kaori; Wand, Gary S; Shrager, Sandi; Seeman, Teresa; Diez Roux, Ana V; Golden, Sherita H

2016-03-01

Evidence of the link between job strain and cortisol levels has been inconsistent. This could be due to failure to account for cortisol variability leading to underestimated standard errors. Our objective was to model the relationship between job strain and the whole cortisol curve, accounting for sources of cortisol variability. Our functional mixed-model approach incorporated all available data-18 samples over 3 days-and uncertainty in estimated relationships. We used employed participants from the Multi-Ethnic Study of Atherosclerosis Stress I Study and data collected between 2002 and 2006. We used propensity score matching on an extensive set of variables to control for sources of confounding. We found that job strain was associated with lower salivary cortisol levels and lower total area under the curve. We found no relationship between job strain and the cortisol awakening response. Our findings differed from those of several previous studies. It is plausible that our results were unique to middle- to older-aged racially, ethnically, and occupationally diverse adults and were therefore not inconsistent with previous research among younger, mostly white samples. However, it is also plausible that previous findings were influenced by residual confounding and failure to propagate uncertainty (i.e., account for the multiple sources of variability) in estimating cortisol features. © The Author 2016. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

A stratification approach using logit-based models for confounder adjustment in the study of continuous outcomes.

PubMed

Tan, Chuen Seng; Støer, Nathalie C; Chen, Ying; Andersson, Marielle; Ning, Yilin; Wee, Hwee-Lin; Khoo, Eric Yin Hao; Tai, E-Shyong; Kao, Shih Ling; Reilly, Marie

2017-01-01

The control of confounding is an area of extensive epidemiological research, especially in the field of causal inference for observational studies. Matched cohort and case-control study designs are commonly implemented to control for confounding effects without specifying the functional form of the relationship between the outcome and confounders. This paper extends the commonly used regression models in matched designs for binary and survival outcomes (i.e. conditional logistic and stratified Cox proportional hazards) to studies of continuous outcomes through a novel interpretation and application of logit-based regression models from the econometrics and marketing research literature. We compare the performance of the maximum likelihood estimators using simulated data and propose a heuristic argument for obtaining the residuals for model diagnostics. We illustrate our proposed approach with two real data applications. Our simulation studies demonstrate that our stratification approach is robust to model misspecification and that the distribution of the estimated residuals provides a useful diagnostic when the strata are of moderate size. In our applications to real data, we demonstrate that parity and menopausal status are associated with percent mammographic density, and that the mean level and variability of inpatient blood glucose readings vary between medical and surgical wards within a national tertiary hospital. Our work highlights how the same class of regression models, available in most statistical software, can be used to adjust for confounding in the study of binary, time-to-event and continuous outcomes.

Forecasting High-Priority Infectious Disease Surveillance Regions: A Socioeconomic Model

PubMed Central

Chan, Emily H.; Scales, David A.; Brewer, Timothy F.; Madoff, Lawrence C.; Pollack, Marjorie P.; Hoen, Anne G.; Choden, Tenzin; Brownstein, John S.

2013-01-01

Background. Few researchers have assessed the relationships between socioeconomic inequality and infectious disease outbreaks at the population level globally. We use a socioeconomic model to forecast national annual rates of infectious disease outbreaks. Methods. We constructed a multivariate mixed-effects Poisson model of the number of times a given country was the origin of an outbreak in a given year. The dataset included 389 outbreaks of international concern reported in the World Health Organization's Disease Outbreak News from 1996 to 2008. The initial full model included 9 socioeconomic variables related to education, poverty, population health, urbanization, health infrastructure, gender equality, communication, transportation, and democracy, and 1 composite index. Population, latitude, and elevation were included as potential confounders. The initial model was pared down to a final model by a backwards elimination procedure. The dependent and independent variables were lagged by 2 years to allow for forecasting future rates. Results. Among the socioeconomic variables tested, the final model included child measles immunization rate and telephone line density. The Democratic Republic of Congo, China, and Brazil were predicted to be at the highest risk for outbreaks in 2010, and Colombia and Indonesia were predicted to have the highest percentage of increase in their risk compared to their average over 1996–2008. Conclusions. Understanding socioeconomic factors could help improve the understanding of outbreak risk. The inclusion of the measles immunization variable suggests that there is a fundamental basis in ensuring adequate public health capacity. Increased vigilance and expanding public health capacity should be prioritized in the projected high-risk regions. PMID:23118271

Farm-scale variation of soil quality indices and association with edaphic properties

USDA-ARS?s Scientific Manuscript database

Soil organisms are indicators of dynamic soil quality because their community structure and population density are sensitive to management changes. However, edaphic properties can also affect soil organisms and high spatial variability can confound their utility for soil evaluation. In the present...

Microcounseling Skill Discrimination Scale: A Methodological Note

ERIC Educational Resources Information Center

Stokes, Joseph; Romer, Daniel

1977-01-01

Absolute ratings on the Microcounseling Skill Discrimination Scale (MSDS) confound the individual's use of the rating scale and actual ability to discriminate effective and ineffective counselor behaviors. This note suggests methods of scoring the MSDS that will eliminate variability attributable to response language and improve the validity of…

Independent effects and interactions of stand diameter, tree diameter, crown class, and age on tree growth in mixed-species, even-aged hardwood stands

Treesearch

D.A. Marquis

1991-01-01

Many studies have shown that initial tree diameter is closely correlated with subsequent tree growth. But initial tree diameter is actually a confounded variable, incorporating both competitive position (crown class) and age.

Complementary health insurance, out- of- pocket expenditures, and health services utilization: A population- based survey.

PubMed

Homaie Rad, Enayatollah; Kavosi, Zahra; Moghadamnia, Mohammad Taghi; Arefnezhad, Masoud; Arefnezhad, Masoumeh; Felezi Nasiri, Banfashe

2017-01-01

Background: Studies have shown that people using complementary health insurances have more access to health services than others. In the present study, we aimed at finding the differences between out- of- pocket payments and health service utilizations in complementary health insurances (CHIs) users and nonusers. Methods: Propensity score matching was used to compare the 2 groups. First, confounder variables were identified, and then propensity score matching was used to compare out- of- pocket expenditures with dental, general physician, hospital inpatient, emergency services, nursing, midwifery, laboratory services, specialists and rehabilitation services utilization. Results: Our results revealed no significant differences between the 2 groups in out- of- pocket health expenditures. Also, the specialist visits, inpatient services at the hospital, and dental services were higher in people who used CHIs compared to nonusers. Conclusion: People did not change their budget share for health care services after using CHIs. The payments were equal for people who were not CHIs users due to the increase in the quantity of the services.

Effect of environmental tobacco smoke on atopic dermatitis among children in Korea.

PubMed

Yi, Okhee; Kwon, Ho-Jang; Kim, Ho; Ha, Mina; Hong, Soo-Jong; Hong, Yun-Chul; Leem, Jong-Han; Sakong, Joon; Lee, Chul Gab; Kim, Su-Young; Kang, Dongmug

2012-02-01

The prevalence of atopic dermatitis is increasing in many countries. Several factors are known to be associated with childhood atopic dermatitis. Environmental tobacco smoke (ETS) is one of the most common indoor pollutants, and children are more vulnerable to ETS exposure than adults are. In this study, the possible association of ETS with atopic dermatitis was evaluated in 7030 individuals aged 6-13 years who participated in the Children's Health and Environment Research study. In addition, predictive factors, such as the allergic history of the parents, children's immunoglobulin E levels and children's history of rhinitis and its association with dermatitis, were assessed. After adjustment for possible confounding variables, atopic dermatitis was found to be highly correlated with ETS, especially among children whose mothers had smoked during pregnancy and/or in the first year after birth (OR=2.06, 95% CI: 1.01-4.22). In conclusion, our results show that childhood exposure to ETS is a major risk factor for atopic dermatitis. Copyright © 2012 Elsevier Inc. All rights reserved.

Cheese consumption and prevalence of overweight and obesity in a Basque adult population: a cross-sectional study.

PubMed

Alegría-Lertxundi, Iker; Rocandio Pablo, Ana; Arroyo-Izaga, Marta

2014-02-01

Studies have reported a negative association between dairy product consumption and weight status. However, not as much research has focused on cheese; therefore, the aim of this study was to study the association between cheese intake and overweight and obesity in a representative Basque adult population. A food frequency questionnaire (FFQ) was obtained from a random sample of 1081 adults (530 males and 551 females, 17-96 years old). Cheese consumption data were expressed as g/1000 kcal/day. The prevalence of overweight/obesity was higher in men (55.1%) than in women (35.4%) (p < 0.001). Participants with low or moderate intake of fresh and processed cheese demonstrated a higher prevalence of excess weight, compared with those with higher consumption. The confounding variables selected in multivariate analysis were: occupational status and age in both genders; and place of residence in men. In conclusion, negative associations were found between consumption of some types of cheese and overweight and obesity in this population.

Breastfeeding and Later Psychosocial Development in the Philippines

PubMed Central

Duazo, Paulita; Avila, Josephine; Kuzawa, Christopher W.

2010-01-01

Objectives Evaluate whether breastfeeding duration predicts later psychosocial development in a large low socioeconomic status (SES) sample in the Philippines. Methods The sample consists of 2,752 children aged 5-6 years who were measured in 2004 as part of the Philippine government's Early Childhood Development Project (ECD). Duration of any breastfeeding was the primary independent variable in regression models predicting a cumulative index of psychosocial development that has been shown previously to predict school readiness. Results In this sample, mothers who breastfed their children for longer tended to have lower educational attainment and to come from lower income households. Despite this, breastfeeding duration was a positive predictor of future psychosocial development (PD) measured in late childhood, but only after adjustment for SES and related confounders. Conclusions These findings add to growing evidence that breastfeeding could provide lasting economic and social benefits and underscore the importance of continuing current public health efforts to promote breastfeeding in the Philippines and across the globe. PMID:20721986

Inseparable phone books demonstration

NASA Astrophysics Data System (ADS)

Balta, Nuri; Çetin, Ali

2017-05-01

This study is aimed at first introducing a well-known discrepant event; inseparable phone books and second, turning it into an experiment for high school or middle school students. This discrepant event could be used especially to indicate how friction force can be effective in producing an unexpected result. Demonstration, discussion, explanation and experiment steps are presented on how to turn a simple discrepant event into an instructional activity. Results showed the relationships between number of pages and force, as well as between amounts of interleave and force. In addition to these, the mathematical equation for the total force between all interleaved pages is derived. As a conclusion, this study demonstrated that not only can phone books be used, but also ordinary books, to investigate this discrepant event. This experiment can be conducted as an example to show the agreement between theoretical and experimental results along with the confounding variables. This discrepant event can be used to create a cognitive conflict in students’ minds about the concepts of ‘force and motion’ and ‘friction force’.

Antidepressants and testicular cancer: cause versus association.

PubMed

Andrade, Chittaranjan

2014-03-01

A data mining study that examined associations between 105 drugs and 55 cancer sites found significant associations between 2 selective serotonin reuptake inhibitors (fluoxetine and paroxetine) and testicular cancer. The study suggested several reasons why these associations merited further investigation. A later study tested specific relationships between 12 antidepressant drugs and testicular cancer and subtypes thereof; whereas significant relationships were again found, these disappeared after adjusting for confounding variables. These 2 studies are educative because they illustrate how false-positive results can easily arise in exploratory research and how confounding may be responsible for statistically significant relationships in study designs that are not randomized controlled trials. © Copyright 2014 Physicians Postgraduate Press, Inc.

Advising as Servant Leadership: Investigating Student Satisfaction

ERIC Educational Resources Information Center

Paul, W. Kohle; Fitzpatrick, Colleen

2015-01-01

Student satisfaction with advising is positively linked to first-year student retention and sophomore persistence to their senior year. However, inconsistencies in the advising literature confound conclusions about the most effective advising approach to elicit student satisfaction. Positive links between the servant leadership approach and…

Food- and health-related correlates of self-reported body mass index among low-income mothers of young children

PubMed Central

McCurdy, Karen; Kisler, Tiffani; Gorman, Kathleen S.; Metallinos-Katsaras, Elizabeth

2015-01-01

Objective Examine how income-related challenges around food and health are associated with variation in self-reported maternal body weight among low-income mothers. Design Cross-sectional, correlational design. Convenience sample recruited from 7 daycare centers and a Supplemental Nutrition Assistance Program outreach project. Maternal self-report data collected between October 2009 and May 2011. Setting Two Northeastern cities. Participants Sample of 166 mothers; 67% overweight or obese, 55% Hispanic, 42% reporting household food insecurity (HFI). Main Outcome Measures Maternal self-reported height and weight to calculate Body Mass Index (BMI). Independent variables: food program participation, supermarket use, 8-item food shopping practices scale, HFI, maternal depressive symptoms, self-rated health (SRH). Analysis Hierarchical multiple regression analysis tested relationships between maternal BMI with the independent variables of interest, adjusting for demographic confounds. Results Shopping practices to stretch food dollars (P = .04), using community food assistance programs (P < .05), and HFI (P < .04) correlated with heavier maternal BMIs; higher SRH corresponded to lower BMIs (P =.004). Conclusions and Implications Some strategies low-income mothers use to manage food resources are associated with heavier BMIs. Nutrition educators, public health practitioners, and researchers need to collaboratively address the associations between these strategies, food insecurity, poor health, and unhealthy weight. PMID:25794991

History of kidney stones as a possible risk factor for chronic kidney disease.

PubMed

Vupputuri, Suma; Soucie, J Michael; McClellan, William; Sandler, Dale P

2004-03-01

The incidence of treated end-stage renal disease has increased progressively in the United States over the past several decades. It has been suggested that kidney stones may be a contributing factor for a small percentage of these patients. We conducted a case-control study utilizing 548 hospital cases and 514 age, race and gender-matched community controls. The main outcome measure was diagnosis of chronic kidney disease, assessed by comprehensive chart review. History of kidney stones and other co-variables were obtained during telephone interviews. This study revealed 16.8% of cases and 6.4% of controls with reported history of kidney stones. The odds ratios (adjusted for confounding variables) for chronic kidney disease (overall), diabetic nephropathy and interstitial nephritis for patients with kidney stones were 1.9 (95% CI: 1.1, 3.3), 2.5 (95% CI: 0.87, 7.0) and 3.4 (95% CI: 1.5, 7.4), respectively. After stratifying by hypertensive status this increased risk persisted only for study participants reporting no history of hypertension. Kidney stones may play a role in the development of chronic kidney disease. Our study suggests that the prevention of kidney stones may be a means of delaying the onset of chronic kidney disease, however, further studies are needed to make conclusive recommendations.

American Visceral Leishmaniasis: Factors Associated with Lethality in the State of São Paulo, Brazil

PubMed Central

Madalosso, Geraldine; Fortaleza, Carlos Magno; Ribeiro, Ana Freitas; Cruz, Lisete Lage; Nogueira, Péricles Alves; Lindoso, José Angelo Lauletta

2012-01-01

Objectives. To identify factors associated with death in visceral leishmaniasis (VL) cases. Patients and Methodology. We evaluated prognostic factors for death from VL in São Paulo state, Brazil, from 1999 to 2005. A prognostic study nested in a clinical cohort was carried out by data analysis of 376 medical files. A comparison between VL fatal cases and survivors was performed for clinical, laboratory, and biological features. Association between variables and death was assessed by univariate analysis, and the multiple logistic regression model was used to determine adjusted odds ratio for death, controlling confounding factors. Results. Data analysis identified 53 fatal cases out of 376 patients, between 1999 and 2005 in São Paulo state. Lethality was 14.1% (53/376), being higher in patients older than fifty years. The main causes of death were sepsis, bleeding, liver failure, and cardiotoxicity due to treatment. Variables significantly associated with death were severe anemia, bleeding, heart failure, jaundice, diarrhea, fever for more than sixty days, age older than fifty years, and antibiotic use. Conclusion. Educational health measures are needed for the general population and continuing education programs for health professionals working in the affected areas with the purpose of identifying and treating early cases, thus preventing the disease evolution towards death. PMID:23024661

Associations between different components of fitness and fatness with academic performance in Chilean youths

PubMed Central

2016-01-01

Objectives To analyze the associations between different components of fitness and fatness with academic performance, adjusting the analysis by sex, age, socio-economic status, region and school type in a Chilean sample. Methods Data of fitness, fatness and academic performance was obtained from the Chilean System for the Assessment of Educational Quality test for eighth grade in 2011 and includes a sample of 18,746 subjects (49% females). Partial correlations adjusted by confounders were done to explore association between fitness and fatness components, and between the academic scores. Three unadjusted and adjusted linear regression models were done in order to analyze the associations of variables. Results Fatness has a negative association with academic performance when Body Mass Index (BMI) and Waist to Height Ratio (WHR) are assessed independently. When BMI and WHR are assessed jointly and adjusted by cofounders, WHR is more associated with academic performance than BMI, and only the association of WHR is positive. For fitness components, strength was the variable most associated with the academic performance. Cardiorespiratory capacity was not associated with academic performance if fatness and other fitness components are included in the model. Conclusions Fitness and fatness are associated with academic performance. WHR and strength are more related with academic performance than BMI and cardiorespiratory capacity. PMID:27761345

Environmental Factors Associated With Social Participation of Older Adults Living in Metropolitan, Urban, and Rural Areas: The NuAge Study

PubMed Central

Cohen, Alan A.; Dubois, Marie-France; Généreux, Mélissa; Richard, Lucie; Therrien, France-Hélène; Payette, Hélène

2015-01-01

Objectives. We compared the social participation of older adults living in metropolitan, urban, and rural areas, and identified associated environmental factors. Methods. From 2004 to 2006, we conducted a cross-sectional study using an age-, gender-, and area-stratified random sample of 1198 adults (aged 67–82 years). We collected data via interviewer-administered questionnaires and derived from Canadian censuses. Results. Social participation did not differ across living areas (P = .09), but after controlling for potential confounding variables, we identified associated area-specific environmental variables. In metropolitan areas, higher social participation was associated with greater proximity to neighborhood resources, having a driver’s license, transit use, and better quality social network (R2 = 0.18). In urban areas, higher social participation was associated with greater proximity to neighborhood resources and having a driver’s license (R2 = 0.11). Finally, in rural areas, higher social participation was associated with greater accessibility to key resources, having a driver’s license, children living in the neighborhood, and more years lived in the current dwelling (R2 = 0.18). Conclusions. To enhance social participation of older adults, public health interventions need to address different environmental factors according to living areas. PMID:25689194

Exclusive Breastfeeding and Other Foods in the First Six Months of Life: Effects on Nutritional Status and Body Composition of Brazilian Children

PubMed Central

Magalhães, Taís C. A.; Vieira, Sarah A.; Priore, Silvia E.; Ribeiro, Andréia Q.; Lamounier, Joel A.; Franceschini, Sylvia C. C.; Sant'Ana, Luciana F. R.

2012-01-01

Objective. To evaluate the effect of exclusive breastfeeding and consumption of other foods in the first six months of life in the nutritional status and body composition of children. Methods. A retrospective cohort study with 185 children aged from 4 to 7 years was monitored during the first months of life in a program of support to breastfeeding. We evaluated weight, height, waist circumference, and body composition by using DEXA. The nutritional status was assessed by the BMI/age index. The parameters of adiposity were classified by using as the cutoff point, the 85th percentile of the sample itself, according to gender and age. Confounding factors considered were variables related to maternal, pregnancy, birth, sociodemographic, health, lifestyle, and diet. Bivariate and multivariate analyses were performed, the latter by means of multiple logistic regression. Results. The median exclusive breastfeeding was 3 months. Of the children, 42.7% received cow's milk and 35.7% received infant formula. Regarding nutritional status, 21.1% of the children showed changes. The variables of infant feeding were not independently associated with nutritional status and body composition of the children and there were no differences between the groups studied. Conclusion. Breastfeeding was not a protective factor to overweight and body fat in children. PMID:23193378

Psychopathology Differences between Batterers and Nonbatterers: Psychosocial Modifiers.

ERIC Educational Resources Information Center

Hamberger, L. Kevin; Hastings, James E.

Research attention on men who batter their female partners has focused on psychological and personality characteristics of the men. However, occupational status, educational attainment, and abuse history may have been confounded with the personality variables studied. This study made within-group and between-group comparisons of batterers and…

Partial Identification of Treatment Effects: Applications to Generalizability

ERIC Educational Resources Information Center

Chan, Wendy

2016-01-01

Results from large-scale evaluation studies form the foundation of evidence-based policy. The randomized experiment is often considered the gold standard among study designs because the causal impact of a treatment or intervention can be assessed without threats of confounding from external variables. Policy-makers have become increasingly…

It Ain't over 'til It's Over: On Foreign Language Anxiety, First Language Deficits, and the Confounding of Variables.

ERIC Educational Resources Information Center

Horwitz, Elaine K.

2000-01-01

Replies on behalf of the authors of a previous article to a critique of their study on foreign language anxiety. Argues that factors other than cognitive-linguistic deficits contribute to problems in foreign language achievement. (Author/VWL)

Multimedia Learning: Are We Still Asking the Wrong Questions?

ERIC Educational Resources Information Center

Rey, Gunter Daniel

2010-01-01

The article discusses problems that arise from comparing different kinds of presentation modes such as texts, pictures or animations with regard to learning outcome. These comparisons are confounded with or depend on other variables like quality of the instructional design, learning content, familiarity with the presentation mode as well as…

The relationship between type D personality and chronic heart failure is not confounded by disease severity as assessed by BNP.

PubMed

Pelle, Aline J; van den Broek, Krista C; Szabó, Balázs; Kupper, Nina

2010-11-05

Psychological factors, like Type D personality (i.e., the tendency to experience negative emotions and to inhibit emotional distress) have been linked to impaired health outcomes. Criticism on the role of psychological factors in cardiac disease has postulated that such constructs may be confounded by disease severity. Hence, we examined whether Type D personality is associated with brain natriuretic peptide (BNP), a sensitive marker of disease severity in chronic heart failure (CHF), in 202 consecutive CHF outpatients. No differences in logBNP levels were found between Type D and non-Type D patients (t(200) = -1.03, p = .30). After adjusting for demographic and clinical confounders, Type D personality remained unassociated with logBNP levels (β=.04, p = .55), whereas older age (β = .27, p<.001), being prescribed beta-blockers (β = .15, p = .02), lower left ventricular ejection fraction (β = -.38, p<.0001), and kidney dysfunction (β = .17, p = .01) were associated with higher logBNP. To conclude, Type D personality was not associated with BNP in CHF outpatients, whereas clinical variables were associated with BNP. These findings oppose the suggestion that Type D personality is confounded by indicators of disease severity. Copyright © 2009 Elsevier Ireland Ltd. All rights reserved.

Accounting for context in studies of health inequalities: a review and comparison of analytic approaches.

PubMed

Schempf, Ashley H; Kaufman, Jay S

2012-10-01

A common epidemiologic objective is to evaluate the contribution of residential context to individual-level disparities by race or socioeconomic position. We reviewed analytic strategies to account for the total (observed and unobserved factors) contribution of environmental context to health inequalities, including conventional fixed effects (FE) and hybrid FE implemented within a random effects (RE) or a marginal model. To illustrate results and limitations of the various analytic approaches of accounting for the total contextual component of health disparities, we used data on births nested within neighborhoods as an applied example of evaluating neighborhood confounding of racial disparities in gestational age at birth, including both a continuous and a binary outcome. Ordinary and RE models provided disparity estimates that can be substantially biased in the presence of neighborhood confounding. Both FE and hybrid FE models can account for cluster level confounding and provide disparity estimates unconfounded by neighborhood, with the latter having greater flexibility in allowing estimation of neighborhood-level effects and intercept/slope variability when implemented in a RE specification. Given the range of models that can be implemented in a hybrid approach and the frequent goal of accounting for contextual confounding, this approach should be used more often. Published by Elsevier Inc.

Antidepressant sales and regional variations of suicide mortality in Germany.

PubMed

Blüml, Victor; Helbich, Marco; Mayr, Michael; Turnwald, Roland; Vyssoki, Benjamin; Lewitzka, Ute; Hartung, Sebastian; Plener, Paul L; Fegert, Jörg M; Kapusta, Nestor D

2017-04-01

Suicides account for over one million deaths per year worldwide with depression among the most important risk factors. Epidemiological research into the relationship between antidepressant utilization and suicide mortality has shown heterogeneous and contradictory results. Different methodological approaches and limitations could at least partially explain varying results. This is the first study assessing the association of suicide mortality and antidepressant sales across Germany using complex statistical approaches in order to control for possible confounding factors including spatial dependency of data. German suicide counts were analyzed on a district level (n = 402) utilizing ecological Poisson regressions within a hierarchical Bayesian framework. Due to significant spatial effects between adjacent districts spatial models were calculated in addition to a baseline non-spatial model. Models were adjusted for several confounders including socioeconomic variables, quality of psychosocial care, and depression prevalence. Separate analyses were performed for Eastern and Western Germany and for different classes of antidepressants (SSRIs and TCAs). Overall antidepressant sales were significantly negatively associated with suicide mortality in the non-spatial baseline model, while after adjusting for spatially structured and unstructured effects the association turned out to be insignificant. In sub-analyses, analogue results were found for SSRIs and TCAs separately. Suicide risk shows a distinct heterogeneous pattern with a pronounced relative risk in Southeast Germany. In conclusion, the results reflect the heterogeneous findings of previous studies on the association between suicide mortality and antidepressant sales and point to the complexity of this hypothesized link. Furthermore, the findings support tailored suicide preventive efforts within high risk areas. Copyright © 2016 Elsevier Ltd. All rights reserved.

Videofluoroscopic and Manometric Evaluation of Pharyngeal and Upper Esophageal Sphincter Function During Swallowing

PubMed Central

Yoon, Kyung Jae; Park, Jung Ho; Park, Jung Hwan; Jung, Il Seok

2014-01-01

Background/Aims The purpose of this study was to determine important manometric metrics for the analysis of pharyngeal and upper esophageal sphincter (UES) function and to investigate the effect of viscosity and other confounding factors on manometric results. Methods Manometric studies were performed on 26 asymptomatic volunteers (12 men and 14 women; age, 19–81 years). The manometric protocol included 5 water swallows (5 mL), 5 barium swallows (5 mL) and 5 yogurt swallows (5 mL). Evaluation of high-resolution manometry parameters including basal pressure of the UES, mesopharyngeal contractile integral (mesopharyngeal CI, mmHg · cm · sec), CI of the hypopharynx and UES (hypopharyngeal CI), relaxation interval of UES, median intrabolus pressure and nadir pressure at UES was performed using MATLAB. Results Mesopharyngeal CIs for barium and yogurt swallows were significantly lower than those for water swallows (both P < 0.05). Hypopharyngeal CIs for water swallows were significantly lower than those for barium swallows (P = 0.004), and median bolus pressure at UES for barium swallows was significantly higher than that for water and yogurt swallows (both P < 0.05). Furthermore, hypopharyngeal CI and median intrabolus pressure at UES were significantly related to age for 3 swallows (all P < 0.01 and P < 0.05, respectively). A significant negative correlation was also noted between nadir pressure at UES and age for water and yogurt swallows (all P < 0.05). Conclusions Manometric measurement of the pharynx and UES varies with respect to viscosity. Moreover, age could be a confounding variable in the interpretation of pharyngeal manometry. PMID:24847841

Explaining the sex difference in depression with a unified bargaining model of anger and depression

PubMed Central

Hagen, Edward H.; Rosenström, Tom

2016-01-01

Background: Women are twice as likely as men to be depressed, a bias that is poorly understood. One evolutionary model proposes that depression is a bargaining strategy to compel reluctant social partners to provide more help in the wake of adversity. An evolutionary model of anger proposes that high upper body strength predisposes individuals to angrily threaten social partners who offer too few benefits or impose too many costs. Here, we propose that when social partners provide too few benefits or impose too many costs, the physically strong become overtly angry and the physically weak become depressed. The sexual dimorphism in upper body strength means that men will be more likely to bargain with anger and physical threats and women with depression. Methodology: We tested this idea using the 2011–12 National Health and Nutrition Examination Survey (NHANES), a large nationally representative sample of US households that included measures of depression and upper body strength. Results: A 2 SD increase in grip strength decreased the odds of depression by more than half (OR=0.4, P=0.0079), which did not appear to be a consequence of confounds with anthropometric, hormonal or socioeconomic variables, but was partially explained by a confound with physical disability. Nevertheless, upper body strength mediated 63% of the effect of sex on depression, but the mediation effect was unexpectedly moderated by age. Conclusions: Low upper body strength is a risk factor for depression, especially in older adults, and the sex difference in body strength appears to explain much of the perplexing sex difference in depression. PMID:26884416

Paternal and maternal alcohol abuse and offspring mental distress in the general population: the Nord-Trøndelag health study

PubMed Central

2012-01-01

Background The degree to which parental alcohol abuse is a risk factor for offspring mental distress is unclear, due to conflicting results of previous research. The inconsistencies in previous findings may be related to sample characteristics and lack of control of confounding or moderating factors. One such factor may be the gender of the abusing parent. Also, other factors, such as parental mental health, divorce, adolescent social network, school functioning or self-esteem, may impact the outcome. This study examines the impact of maternal and paternal alcohol abuse on adolescent mental distress, including potentially confounding, mediating or moderating effects of various variables. Methods Data from the Nord-Trøndelag Health Study (HUNT), a Norwegian population based health survey, from 4012 offspring and their parents were analyzed. Parental alcohol abuse was measured by numerical consumption indicators and CAGE, whereas offspring mental distress was measured by SCL-5, an abbreviated instrument tapping symptoms of anxiety and depression. Statistical method was analysis of variance. Results Maternal alcohol abuse was related to offspring mental distress, whereas no effect could be shown of paternal alcohol abuse. Effects of maternal alcohol abuse was partly mediated by parental mental distress, offspring social network and school functioning. However, all effects were relatively small. Conclusions The results indicate graver consequences for offspring of alcohol abusing mothers compared to offspring of alcohol abusing fathers. However, small effect sizes suggest that adolescent offspring of alcohol abusing parents in general manage quite well. PMID:22708789

Adult consequences of growth failure in early childhood123

PubMed Central

Hoddinott, John; Behrman, Jere R; Maluccio, John A; Melgar, Paul; Quisumbing, Agnes R; Ramirez-Zea, Manuel; Stein, Aryeh D; Yount, Kathryn M

2013-01-01

Background: Growth failure is associated with adverse consequences, but studies need to control adequately for confounding. Objective: We related height-for-age z scores (HAZs) and stunting at age 24 mo to adult human capital, marriage, fertility, health, and economic outcomes. Design: In 2002–2004, we collected data from 1338 Guatemalan adults (aged 25–42 y) who were studied as children in 1969–1977. We used instrumental variable regression to correct for estimation bias and adjusted for potentially confounding factors. Results: A 1-SD increase in HAZ was associated with more schooling (0.78 grades) and higher test scores for reading and nonverbal cognitive skills (0.28 and 0.25 SDs, respectively), characteristics of marriage partners (1.39 y older, 1.02 grade more schooling, and 1.01 cm taller) and, for women, a higher age at first birth (0.77 y) and fewer number of pregnancies and children (0.63 and 0.43, respectively). A 1-SD increase in HAZ was associated with increased household per capita expenditure (21%) and a lower probability of living in poverty (10 percentage points). Conversely, being stunted at 2 y was associated with less schooling, a lower test performance, a lower household per capita expenditure, and an increased probability of living in poverty. For women, stunting was associated with a lower age at first birth and higher number of pregnancies and children. There was little relation between either HAZ or stunting and adult health. Conclusion: Growth failure in early life has profound adverse consequences over the life course on human, social, and economic capital. PMID:24004889

Microstructural brain abnormalities in medication-free patients with major depressive disorder: a systematic review and meta-analysis of diffusion tensor imaging

PubMed Central

Jiang, Jing; Zhao, You-Jin; Hu, Xin-Yu; Du, Ming-Ying; Chen, Zi-Qi; Wu, Min; Li, Kai-Ming; Zhu, Hong-Yan; Kumar, Poornima; Gong, Qi-Yong

2017-01-01

Background Multiple meta-analyses of diffusion tensor imaging (DTI) studies have reported impaired white matter integrity in patients with major depressive disorder (MDD). However, owing to inclusion of medicated patients in these studies, it is difficult to conclude whether these reported alterations are associated with MDD or confounded by medication effects. A meta-analysis of DTI studies on medication-free (medication-naive and medication washout) patients with MDD would therefore be necessary to disentangle MDD-specific effects. Methods We analyzed white matter alterations between medication-free patients with MDD and healthy controls using anisotropic effect size–signed differential mapping (AES-SDM). We used DTI query software for fibre tracking. Results Both pooled and subgroup meta-analyses in medication washout patients showed robust fractional anisotropy (FA) reductions in white matter of the right cerebellum hemispheric lobule, body of the corpus callosum (CC) and bilateral superior longitudinal fasciculus III (SLF III), whereas FA reductions in the genu of the CC and right anterior thalamic projections were seen in only medication-naive patients. Fibre tracking showed that the main tracts with observed FA reductions included the right cerebellar tracts, body of the CC, bilateral SLF III and arcuate fascicle. Limitations The analytic techniques, patient characteristics and clinical variables of the included studies were heterogeneous; we could not exclude the effects of nondrug therapies owing to a lack of data. Conclusion By excluding the confounding influences of current medication status, findings from the present study may provide a better understanding of the underlying neuropathology of MDD. PMID:27780031

What are the most effective risk-reduction strategies in sport concussion?

PubMed

Benson, Brian W; McIntosh, Andrew S; Maddocks, David; Herring, Stanley A; Raftery, Martin; Dvorák, Jirí

2013-04-01

To critically review the evidence to determine the efficacy and effectiveness of protective equipment, rule changes, neck strength and legislation in reducing sport concussion risk. Electronic databases, grey literature and bibliographies were used to search the evidence using Medical Subject Headings and text words. Inclusion/exclusion criteria were used to select articles for the clinical equipment studies. The quality of evidence was assessed using epidemiological criteria regarding internal/external validity (eg, strength of design, sample size/power, bias and confounding). No new valid, conclusive evidence was provided to suggest the use of headgear in rugby, or mouth guards in American football, significantly reduced players' risk of concussion. No evidence was provided to suggest an association between neck strength increases and concussion risk reduction. There was evidence in ice hockey to suggest fair-play rules and eliminating body checking among 11-years-olds to 12-years-olds were effective injury prevention strategies. Evidence is lacking on the effects of legislation on concussion prevention. Equipment self-selection bias was a common limitation, as was the lack of measurement and control for potential confounding variables. Lastly, helmets need to be able to protect from impacts resulting in a head change in velocities of up to 10 and 7 m/s in professional American and Australian football, respectively, as well as reduce head resultant linear and angular acceleration to below 50 g and 1500 rad/s(2), respectively, to optimise their effectiveness. A multifactorial approach is needed for concussion prevention. Future well-designed and sport-specific prospective analytical studies of sufficient power are warranted.

Depressive Symptoms and Salivary Telomere Length in a Probability Sample of Middle-Aged and Older Adults

PubMed Central

Whisman, Mark A.; Richardson, Emily D.

2016-01-01

Objective To examine the association between depressive symptoms and salivary telomere length in a probability sample of middle-aged and older adults, evaluate age and sex as potential moderators of this association, and test whether this association was incremental to potential confounds. Methods Participants were 3,609 individuals from the 2008 wave of the Health and Retirement Study. Telomere length assays were performed using quantitative real-time polymerase chain reaction (qPCR) on DNA extracted from saliva samples. Depressive symptoms were assessed via interview, and health and lifestyle factors, traumatic life events, and neuroticism were assessed via self-report. Regression analyses were conducted to examine the associations between predictor variables and salivary telomere length. Results After adjusting for demographics, depressive symptoms were negatively associated with salivary telomere length (b = −.003, p = .014). Furthermore, this association was moderated by sex (b = .005, p = .011), such that depressive symptoms were significantly and negatively associated with salivary telomere length for men (b = −.006, p < .001) but not for women (b = −.001, p = .644). The negative association between depressive symptoms and salivary telomere length in men remained statistically significant after additionally adjusting for cigarette smoking, body mass index, chronic health conditions, childhood and lifetime exposure to traumatic life events, and neuroticism. Conclusions Higher levels of depressive symptoms were associated with shorter salivary telomeres in men and this association was incremental to several potential confounds. Shortened telomeres may help account for the association between depression and poor physical health and mortality. PMID:28029664

Effects of the Non-Nutritive Sweeteners on Glucose Metabolism and Appetite Regulating Hormones: Systematic Review of Observational Prospective Studies and Clinical Trials

PubMed Central

Romo-Romo, Alonso; Aguilar-Salinas, Carlos A.; Brito-Córdova, Griselda X.; Gómez Díaz, Rita A.; Vilchis Valentín, David

2016-01-01

Background The effects of non-nutritive sweeteners (NNS) on glucose metabolism and appetite regulating hormones are not clear. There is an ongoing debate concerning NNS use and deleterious changes in metabolism. Objectives The aim of this review is to analyze the scientific available evidence regarding the effects of NNS on glucose metabolism and appetite regulating hormones. Data Sources and Study Eligibility Criteria We identified human observational studies evaluating the relation between NNS consumption and obesity, diabetes, and metabolic syndrome, in addition to clinical trials evaluating the effects of NNS in glucose metabolism and appetite regulating hormones. Results Fourteen observational studies evaluating the association between NNS consumption and the development of metabolic diseases and twenty-eight clinical trials studying the effects of NNS on metabolism were included. Finally, two meta-analyses evaluating the association between the consumption of NNS-containing beverages and the development of type 2 diabetes were identified. Conclusions Some observational studies suggest an association between NNS consumption and development of metabolic diseases; however, adiposity is a confounder frequently found in observational studies. The effects of the NNS on glucose metabolism are not clear. The results of the identified clinical trials are contradictory and are not comparable because of the major existing differences between them. Studies evaluating specific NNS, with an adequate sample size, including a homogeneous study group, identifying significant comorbidities, with an appropriate control group, with an appropriate exposure time, and considering adjustment for confounder variables such as adiposity are needed. PMID:27537496

The association of remotely-sensed outdoor temperature with blood pressure levels in REGARDS: a cross-sectional study of a large, national cohort of African-American and white participants

PubMed Central

2011-01-01

Background Evidence is mounting regarding the clinically significant effect of temperature on blood pressure. Methods In this cross-sectional study the authors obtained minimum and maximum temperatures and their respective previous week variances at the geographic locations of the self-reported residences of 26,018 participants from a national cohort of blacks and whites, aged 45+. Linear regression of data from 20,623 participants was used in final multivariable models to determine if these temperature measures were associated with levels of systolic or diastolic blood pressure, and whether these relations were modified by stroke-risk region, race, education, income, sex hypertensive medication status, or age. Results After adjustment for confounders, same-day maximum temperatures 20°F lower had significant associations with 1.4 mmHg (95% CI: 1.0, 1.9) higher systolic and 0.5 mmHg (95% CI: 0.3, 0.8) higher diastolic blood pressures. Same-day minimum temperatures 20°F lower had a significant association with 0.7 mmHg (95% CI: 0.3, 1.0) higher systolic blood pressures but no significant association with diastolic blood pressure differences. Maximum and minimum previous-week temperature variabilities showed significant but weak relationships with blood pressures. Parameter estimates showed effect modification of negligible magnitude. Conclusions This study found significant associations between outdoor temperature and blood pressure levels, which remained after adjustment for various confounders including season. This relationship showed negligible effect modification. PMID:21247466

Early cognitive development in children born to women with epilepsy: a prospective report.

PubMed

Bromley, Rebecca L; Mawer, George; Love, Jenna; Kelly, James; Purdy, Laura; McEwan, Lauren; Briggs, Maria; Clayton-Smith, Jill; Shi, Xin; Sin, Xin; Baker, Gus A

2010-10-01

In this prospective study the early cognitive development of children born to women with epilepsy (n = 198) was assessed and compared to a group of children representative of the general population (n = 230). The children were assessed when younger than the age of 2 years using the Griffiths Mental Development Scales, either in their local participating hospital or in their home. The assessments were completed by an assessor who was blinded to whether the child's mother had epilepsy and to antiepileptic drug type. Children exposed to sodium valproate had a statistically significant increased risk of delayed early development in comparison to the control children. Linear regression analysis showed a statistically significant effect of sodium valproate exposure on the child's overall developmental level that was not accounted for by confounding variables. Delayed early development is also noted for children within an ad hoc group of less commonly utilized antiepileptic drugs, although conclusions cannot be drawn due to the size of this group (n = 13). Children exposed to either carbamazepine or lamotrigine in utero did not differ significantly in their overall developmental ability. Differences noted in specific developmental areas for these two groups were not statistically significant after the control for confounders such as socioeconomic status and maternal IQ. Women with epilepsy should be informed of the risks posed to their potential offspring prior to pregnancy to allow for informed decisions regarding treatment. Children exposed in utero to antiepileptic drugs should be monitored throughout childhood to allow for early intervention when necessary. Wiley Periodicals, Inc. © 2010 International League Against Epilepsy.

Measurement of intracranial pressure and short-term outcomes of patients with traumatic brain injury: a propensity-matched analysis

PubMed Central

Ferreira, Cesar Biselli; Bassi, Estevão; Lucena, Lucas; Carreta, Hernandez; Miranda, Leandro Costa; Tierno, Paulo Fernando Guimarães Mazorcchi; Amorim, Robson Luis; Zampieri, Fernando Godinho; Malbouisson, Luis Marcelo Sá

2015-01-01

Objective To assess the impact of intracranial pressure monitoring on the short-term outcomes of traumatic brain injury patients. Methods Retrospective observational study including 299 consecutive patients admitted due to traumatic brain injury from January 2011 through July 2012 at a Level 1 trauma center in São Paulo, Brazil. Patients were categorized in two groups according to the measurement of intracranial pressure (measured intracranial pressure and non-measured intracranial pressure groups). We applied a propensity-matched analysis to adjust for possible confounders (variables contained in the Crash Score prognostic algorithm). Results Global mortality at 14 days (16%) was equal to that observed in high-income countries in the CRASH Study and was better than expected based on the CRASH calculator score (20.6%), with a standardized mortality ratio of 0.77. A total of 28 patients received intracranial pressure monitoring (measured intracranial pressure group), of whom 26 were paired in a 1:1 fashion with patients from the non-measured intracranial pressure group. There was no improvement in the measured intracranial pressure group compared to the non-measured intracranial pressure group regarding hospital mortality, 14-day mortality, or combined hospital and chronic care facility mortality. Survival up to 14 days was also similar between groups. Conclusion Patients receiving intracranial pressure monitoring tend to have more severe traumatic brain injuries. However, after adjusting for multiple confounders using propensity scoring, no benefits in terms of survival were observed among intracranial pressure-monitored patients and those managed with a systematic clinical protocol. PMID:26761468

Effects of various factors on Doppler ultrasonographic measurements of radial and coccygeal arterial blood pressure in privately owned, conscious cats.

PubMed

Whittemore, Jacqueline C; Nystrom, Michael R; Mawby, Dianne I

2017-04-01

OBJECTIVE To assess the effects of age, body condition score (BCS), and muscle condition score (MCS) on radial and coccygeal systolic arterial blood pressure (SAP) in cats. DESIGN Prospective randomized trial. ANIMALS 66 privately owned cats enrolled between May and December 2010. PROCEDURES BCS and MCS of cats were assessed by 2 investigators; SAP was measured via Doppler ultrasonic flow detector, with cats positioned in right lateral or sternal recumbency for measurements at the radial or coccygeal artery, respectively, with order of site randomized. Associations among variables were assessed through correlation coefficients, partial correlation coefficients, and ANCOVA. RESULTS Interrater reliability for BCS and MCS assessment was high (correlation coefficients, 0.95 and 0.83, respectively). No significant effect was identified for order of SAP measurement sites. Coccygeal and radial SAP were positively correlated (ρ = 0.45). The median difference in coccygeal versus radial SAP was 19 mm Hg, but differences were not consistently positive or negative. Radial SAP was positively correlated with age (ρ = 0.48) and negatively correlated with MCS (ρ = -0.30). On the basis of the correlation analysis, the association between radial SAP and MCS reflected the confounding influence of age. Coccygeal SAP was not significantly correlated with age, BCS, or MCS. CONCLUSIONS AND CLINICAL RELEVANCE Use of the coccygeal artery is recommended to reduce the confounding effects of age and sarcopenia on Doppler ultrasonographic SAP measurements in cats. Additionally, monitoring for changes in MCS is recommended for cats undergoing serial SAP measurement.

Pulmonary function and fuel use: A population survey

PubMed Central

Saha, Asim; Mohan Rao, N; Kulkarni, PK; Majumdar, PK; Saiyed, HN

2005-01-01

Background In the backdrop of conflicting reports (some studies reported adverse outcomes of biomass fuel use whereas few studies reported absence of any association between adverse health effect and fuel use, may be due to presence of large number of confounding variables) on the respiratory health effects of biomass fuel use, this cross sectional survey was undertaken to understand the role of fuel use on pulmonary function. Method This study was conducted in a village of western India involving 369 randomly selected adult subjects (165 male and 204 female). All the subjects were interviewed and were subjected to pulmonary function test. Analysis of covariance was performed to compare the levels of different pulmonary function test parameters in relation to different fuel use taking care of the role of possible confounding factors. Results This study showed that biomass fuel use (especially wood) is an important factor for deterioration of pulmonary function (particularly in female). FEV1 (p < .05), FEV1 % (p < .01), PEFR (p < .05) and FEF25–75 (p < .01) values were significantly lower in biomass fuel using females than nonusers. Comparison of only biomass fuel use vs. only LPG (Liquefied Petroleum Gas) use and only wood vs. only LPG use has showed that LPG is a safer fuel so far as deterioration of pulmonary function is concerned. This study observes some deterioration of pulmonary function in the male subjects also, who came from biomass fuel using families. Conclusion This study concluded that traditional biomass fuels like wood have adverse effects on pulmonary function. PMID:16255784

Is There a Relationship Between the Concentration of Same-Sex Couples and Tobacco Retailer Density?

PubMed Central

Pan, William K.; Henriksen, Lisa; Goldstein, Adam O.; Ribisl, Kurt M.

2016-01-01

Background: Tobacco use is markedly higher among lesbian, gay, and bisexual populations than heterosexuals. Higher density of tobacco retailers is found in neighborhoods with lower income and more racial/ethnic minorities. Same-sex couples tend to live in similar neighborhoods, but the association of this demographic with tobacco retailer density has not been examined. Methods: For a national sample of 97 US counties, we calculated the number of tobacco retailers per 1000 persons and rates of same-sex couples per 1000 households in each census tract (n = 17 941). Using spatial regression, we examined the association of these variables in sex-stratified models, including neighborhood demographics and other environmental characteristics to examine confounding. Results: Results from spatial regression show that higher rates of both female and male same-sex couples were associated with a higher density of tobacco retailers. However the magnitude of this association was small. For female couples, the association was not significant after controlling for area-level characteristics, such as percent black, percent Hispanic, median household income, the presence of interstate highways, and urbanicity, which are neighborhood correlates of higher tobacco retailer density. For male couples, the association persisted after control for these characteristics. Conclusion: Same-sex couples reside in areas with higher tobacco retailer density, and for men, this association was not explained by neighborhood confounders, such as racial/ethnic composition and income. While lesbian, gay, and bisexual disparities in tobacco use may be influenced by neighborhood environment, the magnitude of the association suggests other explanations of these disparities remain important areas of research. PMID:25744959

What is the association between wealth and mental health?

PubMed

Carter, K N; Blakely, T; Collings, S; Imlach Gunasekara, F; Richardson, K

2009-03-01

Socioeconomic inequalities in mental health have been shown in a number of populations. This study aims to investigate the association between asset wealth and psychological distress in New Zealand and whether it is independent of other socioeconomic measures and baseline health status. Data for this study were from the first three waves of the Survey of Families, Income and Employment (SoFIE) conducted in New Zealand (2002-2004/05) (n = 15 340). The Kessler-10 was used as a measure of psychological distress. The association of quintiles of wealth with psychological distress was investigated using logistic regression, controlling for confounders, socioeconomic variables and prior health status. The odds ratio (OR) of reporting high psychological distress were greater in the lowest wealth quintile compared with the highest (OR 3.06, 95% CI 2.68 to 3.50). Adjusting for age and sex did not alter the relationship; however, adjusting for income and area deprivation attenuated the OR to 1.73 (95% CI 1.48 to 2.04). Further controlling for baseline health status reduced the OR to 1.45 (95% CI 1.23 to 1.71), although the confidence interval still excluded the null. Inequalities in wealth are strongly associated with psychological distress, over and above other confounding demographic variables and baseline health status. Much, but not all, of that association is confounded by adult socioeconomic position. This suggests that policy measures to improve asset wealth, through savings and home ownership, may have positive health implications and help to reduce health inequalities.

Multisample adjusted U-statistics that account for confounding covariates.

PubMed

Satten, Glen A; Kong, Maiying; Datta, Somnath

2018-06-19

Multisample U-statistics encompass a wide class of test statistics that allow the comparison of 2 or more distributions. U-statistics are especially powerful because they can be applied to both numeric and nonnumeric data, eg, ordinal and categorical data where a pairwise similarity or distance-like measure between categories is available. However, when comparing the distribution of a variable across 2 or more groups, observed differences may be due to confounding covariates. For example, in a case-control study, the distribution of exposure in cases may differ from that in controls entirely because of variables that are related to both exposure and case status and are distributed differently among case and control participants. We propose to use individually reweighted data (ie, using the stratification score for retrospective data or the propensity score for prospective data) to construct adjusted U-statistics that can test the equality of distributions across 2 (or more) groups in the presence of confounding covariates. Asymptotic normality of our adjusted U-statistics is established and a closed form expression of their asymptotic variance is presented. The utility of our approach is demonstrated through simulation studies, as well as in an analysis of data from a case-control study conducted among African-Americans, comparing whether the similarity in haplotypes (ie, sets of adjacent genetic loci inherited from the same parent) occurring in a case and a control participant differs from the similarity in haplotypes occurring in 2 control participants. Copyright © 2018 John Wiley & Sons, Ltd.

Does Anaemia Have Major Public Health Importance in Children Aged 6-59 Months in the Duggina Fanigo District of Wolaita Zone, Southern Ethiopia?

PubMed

Tiku, Yohannes Samuel; Mekonnen, Tefera Chane; Workie, Shimelash Bitew; Amare, Endale

2018-01-01

Globally, a large number of children aged 6-59 months are affected by anaemia. In Ethiopia, like other developing countries, more than 40% of children under 5 years are affected by anaemia. Anaemia during infancy and childhood period is associated with poor health and impaired cognitive development, leading to reduced academic achievement and earning potential in their adult life. The aim of this research was to assess whether anaemia remained a major public health problem among children aged 6-59 months or not in Duggina Fanigo District of Wolaita Zone, South Ethiopia in 2016. A community-based cross-sectional study was conducted from February to March 2016, on 404 mothers with children aged 6-59 months who were selected through the systematic sampling method. Socio-demographic and other data on associated factors was collected using a pre-tested questionnaire. Capillary blood was taken from the fingertip of each child and hemoglobin was measured using Haemo-Cue digital photometer. All the necessary safety measures were taken during blood collection. Data analysis was made using SPSS version 21. Multivariable logistic regression analysis was used to assess the association of independent variables with outcome variables and to control the possible confounding factors. The overall prevalence of anaemia was 51.4%. Anaemia was common among young children as compared to older children. After controlling the effect of confounding and adjusting for age, gender and altitude, explanatory variables like low dietary diversity (AOR = 3.24; 95% CI [1.68-6.23]), food insecurity (AOR = 3.63; 95% CI [2.18-6.04]), stunting (AOR = 2.60; 95% CI [1.56-4.35]), underweight (AOR = 2.46; 95% CI [1.29-4.67]) and fever within 2 weeks (AOR = 2.49; 95% CI [1.29-4.81]) prior to the survey were significantly associated with anaemia. In conclusion, the overall prevalence of anaemia among children aged 6-59 months has remained a major public health importance in the study area. Integrated efforts need to be prioritized to improve the health as well as the nutritional status of children aged 6-59 months through appropriate feeding practices in infants and children. © 2017 S. Karger AG, Basel.

International Monetary Fund Programs and Tuberculosis Outcomes in Post-Communist Countries

PubMed Central

Stuckler, David; King, Lawrence P; Basu, Sanjay

2008-01-01

Background Previous studies have indicated that International Monetary Fund (IMF) economic programs have influenced health-care infrastructure in recipient countries. The post-communist Eastern European and former Soviet Union countries experienced relatively similar political and economic changes over the past two decades, and participated in IMF programs of varying size and duration. We empirically examine how IMF programs related to changes in tuberculosis incidence, prevalence, and mortality rates among these countries. Methods and Findings We performed multivariate regression of two decades of tuberculosis incidence, prevalence, and mortality data against variables potentially influencing tuberculosis program outcomes in 21 post-communist countries for which comparative data are available. After correcting for confounding variables, as well as potential detection, selection, and ecological biases, we observed that participating in an IMF program was associated with increased tuberculosis incidence, prevalence, and mortality rates by 13.9%, 13.2%, and 16.6%, respectively. Each additional year of participation in an IMF program was associated with increased tuberculosis mortality rates by 4.1%, and each 1% increase in IMF lending was associated with increased tuberculosis mortality rates by 0.9%. On the other hand, we estimated a decrease in tuberculosis mortality rates of 30.7% (95% confidence interval, 18.3% to 49.5%) associated with exiting the IMF programs. IMF lending did not appear to be a response to worsened health outcomes; rather, it appeared to be a precipitant of such outcomes (Granger- and Sims-causality tests), even after controlling for potential political, socioeconomic, demographic, and health-related confounders. In contrast, non-IMF lending programs were connected with decreased tuberculosis mortality rates (−7.6%, 95% confidence interval, −1.0% to −14.1%). The associations observed between tuberculosis mortality and IMF programs were similar to those observed when evaluating the impact of IMF programs on tuberculosis incidence and prevalence. While IMF programs were connected with large reductions in generalized government expenditures, tuberculosis program coverage, and the number of physicians per capita, non-IMF lending programs were not significantly associated with these variables. Conclusions IMF economic reform programs are associated with significantly worsened tuberculosis incidence, prevalence, and mortality rates in post-communist Eastern European and former Soviet countries, independent of other political, socioeconomic, demographic, and health changes in these countries. Future research should attempt to examine how IMF programs may have related to other non-tuberculosis–related health outcomes. PMID:18651786

What is the relationship between renal function and visit-to-visit blood pressure variability in primary care? Retrospective cohort study from routinely collected healthcare data.

PubMed

Lasserson, Daniel S; Scherpbier de Haan, Nynke; de Grauw, Wim; van der Wel, Mark; Wetzels, Jack F; O'Callaghan, Christopher A

2016-06-10

To determine the relationship between renal function and visit-to-visit blood pressure (BP) variability in a cohort of primary care patients. Retrospective cohort study from routinely collected healthcare data. Primary care in Nijmegen, the Netherlands, from 2007 to 2012. 19 175 patients who had a measure of renal function, and 7 separate visits with BP readings in the primary care record. Visit-to-visit variability in systolic BP, calculated from the first 7 office measurements, including SD, successive variation, absolute real variation and metrics of variability shown to be independent of mean. Multiple linear regression was used to analyse the influence of estimated glomerular filtration rate (eGFR) on BP variability measures with adjustment for age, sex, diabetes, mean BP, proteinuria, cardiovascular disease, time interval between measures and antihypertensive use. In the patient cohort, 57% were women, mean (SD) age was 65.5 (12.3) years, mean (SD) eGFR was 75.6 (18.0) mL/min/1.73m(2) and SD systolic BP 148.3 (21.4) mm Hg. All BP variability measures were negatively correlated with eGFR and positively correlated with age. However, multiple linear regressions demonstrated consistent, small magnitude negative relationships between eGFR and all measures of BP variability adjusting for confounding variables. Worsening renal function is associated with small increases in measures of visit-to-visit BP variability after adjustment for confounding factors. This is seen across the spectrum of renal function in the population, and provides a mechanism whereby chronic kidney disease may raise the risk of cardiovascular events. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

The occupational impact of sleep quality and insomnia symptoms.

PubMed

Kucharczyk, Erica R; Morgan, Kevin; Hall, Andrew P

2012-12-01

While the importance of assessing the occupational consequences of insomnia is emphasized in clinical nosologies and research guidelines, there is little consensus on which aspects of occupational performance should be assessed, the most methodologically justifiable measures of insomnia and work performance, and how outcomes should be reported. The present review was designed to summarize and methodologically critique the assessment of those aspects of occupational performance most impacted by (or most frequently associated with) insomnia symptoms. The 30 studies which met the review inclusion criteria broadly addressed six domains of occupational functioning: absenteeism; workplace accidents; productivity; punctuality; job satisfaction and career progression. Collectively, study outcomes support the conclusions that insomnia symptoms: are consistently associated with excess absenteeism; elevate accident risk in the workplace; reduce subjectively experienced workplace productivity (at least in the shorter term); inhibit career progression; and can degrade job satisfaction. Study outcomes do not support the conclusion that people with insomnia are significantly less punctual than other workers. The overall value of the occupational sleep-health literature, however, is limited by a lack of comparability among studies. In particular, there is a clear need to standardize definitions of sleep and occupational outcomes, and to recognize the confounding influence of health variables on occupational performance and sleep. Copyright © 2012 Elsevier Ltd. All rights reserved.

Does partial Granger causality really eliminate the influence of exogenous inputs and latent variables?

PubMed

Roelstraete, Bjorn; Rosseel, Yves

2012-04-30

Partial Granger causality was introduced by Guo et al. (2008) who showed that it could better eliminate the influence of latent variables and exogenous inputs than conditional G-causality. In the recent literature we can find some reviews and applications of this type of Granger causality (e.g. Smith et al., 2011; Bressler and Seth, 2010; Barrett et al., 2010). These articles apparently do not take into account a serious flaw in the original work on partial G-causality, being the negative F values that were reported and even proven to be plausible. In our opinion, this undermines the credibility of the obtained results and thus the validity of the approach. Our study is aimed to further validate partial G-causality and to find an answer why negative partial Granger causality estimates were reported. Time series were simulated from the same toy model as used in the original paper and partial and conditional causal measures were compared in the presence of confounding variables. Inference was done parametrically and using non-parametric block bootstrapping. We counter the proof that partial Granger F values can be negative, but the main conclusion of the original article remains. In the presence of unknown latent and exogenous influences, it appears that partial G-causality will better eliminate their influence than conditional G-causality, at least when non-parametric inference is used. Copyright © 2012 Elsevier B.V. All rights reserved.

Roll-Tilt Perception Using a Somatosensory Bar Task

NASA Technical Reports Server (NTRS)

Black, F. O.; Wade, S. W.; Arshi, A.

1999-01-01

Visual estimates of roll-tilt perception during static roll-tilt are confounded by an offset due to the ocular counterroll that simultaneously occurs. An alternative, non-visual ('somatosensory') measure of roll-tilt perception was developed which is not contaminated by this offset. The aims of this study were to determine: 1) inter-subject variability of somatosensory settings across test session in normal subjects and patients with unilateral or bilateral vestibular loss and 2) intra-subject variability of settings across test session in normal subjects.

Supervised normalization of microarrays

PubMed Central

Mecham, Brigham H.; Nelson, Peter S.; Storey, John D.

2010-01-01

Motivation: A major challenge in utilizing microarray technologies to measure nucleic acid abundances is ‘normalization’, the goal of which is to separate biologically meaningful signal from other confounding sources of signal, often due to unavoidable technical factors. It is intuitively clear that true biological signal and confounding factors need to be simultaneously considered when performing normalization. However, the most popular normalization approaches do not utilize what is known about the study, both in terms of the biological variables of interest and the known technical factors in the study, such as batch or array processing date. Results: We show here that failing to include all study-specific biological and technical variables when performing normalization leads to biased downstream analyses. We propose a general normalization framework that fits a study-specific model employing every known variable that is relevant to the expression study. The proposed method is generally applicable to the full range of existing probe designs, as well as to both single-channel and dual-channel arrays. We show through real and simulated examples that the method has favorable operating characteristics in comparison to some of the most highly used normalization methods. Availability: An R package called snm implementing the methodology will be made available from Bioconductor (http://bioconductor.org). Contact: jstorey@princeton.edu Supplementary information: Supplementary data are available at Bioinformatics online. PMID:20363728

Valence, arousal, familiarity, concreteness, and imageability ratings for 292 two-character Chinese nouns in Cantonese speakers in Hong Kong.

PubMed

Yee, Lydia T S

2017-01-01

Words are frequently used as stimuli in cognitive psychology experiments, for example, in recognition memory studies. In these experiments, it is often desirable to control for the words' psycholinguistic properties because differences in such properties across experimental conditions might introduce undesirable confounds. In order to avoid confounds, studies typically check to see if various affective and lexico-semantic properties are matched across experimental conditions, and so databases that contain values for these properties are needed. While word ratings for these variables exist in English and other European languages, ratings for Chinese words are not comprehensive. In particular, while ratings for single characters exist, ratings for two-character words-which often have different meanings than their constituent characters, are scarce. In this study, ratings for 292 two-character Chinese nouns were obtained from Cantonese speakers in Hong Kong. Affective variables, including valence and arousal, and lexico-semantic variables, including familiarity, concreteness, and imageability, were rated in the study. The words were selected from a film subtitle database containing word frequency information that could be extracted and listed alongside the resulting ratings. Overall, the subjective ratings showed good reliability across all rated dimensions, as well as good reliability within and between the different groups of participants who each rated a subset of the words. Moreover, several well-established relationships between the variables found consistently in other languages were also observed in this study, demonstrating that the ratings are valid. The resulting word database can be used in studies where control for the above psycholinguistic variables is critical to the research design.

Meteorological influences on the interannual variability of meningitis incidence in northwest Nigeria.

NASA Astrophysics Data System (ADS)

Abdussalam, Auwal; Monaghan, Andrew; Dukic, Vanja; Hayden, Mary; Hopson, Thomas; Leckebusch, Gregor

2013-04-01

Northwest Nigeria is a region with high risk of bacterial meningitis. Since the first documented epidemic of meningitis in Nigeria in 1905, the disease has been endemic in the northern part of the country, with epidemics occurring regularly. In this study we examine the influence of climate on the interannual variability of meningitis incidence and epidemics. Monthly aggregate counts of clinically confirmed hospital-reported cases of meningitis were collected in northwest Nigeria for the 22-year period spanning 1990-2011. Several generalized linear statistical models were fit to the monthly meningitis counts, including generalized additive models. Explanatory variables included monthly records of temperatures, humidity, rainfall, wind speed, sunshine and dustiness from weather stations nearest to the hospitals, and a time series of polysaccharide vaccination efficacy. The effects of other confounding factors -- i.e., mainly non-climatic factors for which records were not available -- were estimated as a smooth, monthly-varying function of time in the generalized additive models. Results reveal that the most important explanatory climatic variables are mean maximum monthly temperature, relative humidity and dustiness. Accounting for confounding factors (e.g., social processes) in the generalized additive models explains more of the year-to-year variation of meningococcal disease compared to those generalized linear models that do not account for such factors. Promising results from several models that included only explanatory variables that preceded the meningitis case data by 1-month suggest there may be potential for prediction of meningitis in northwest Nigeria to aid decision makers on this time scale.

Is the Association of Subjective SES and Self-Rated Health Confounded by Negative Mood? An Experimental Approach

PubMed Central

Kraus, Michael W.; Adler, Nancy; David Chen, Teh-Way

2012-01-01

Objective Lower subjective socioeconomic status (SSS) consistently shows associations with poorer health with the strongest relationships emerging with global self-rated health. Though often interpreted as reflecting the impact of low SSS on health, the association could also arise from confounding SSS with negative affect. In this research we sought to determine if negative affect confounds, or alternatively, is on the causal pathway linking SSS to self-rated health. Methods 300 adult participants—recruited from throughout the United States—were randomized to experience sadness, shame, or a neutral mood induction wherein they wrote about and visualized a particularly emotionally evocative event. Participants subsequently completed measures of SSS, self-rated health, depression, and negative mood. Results Consistent with predictions, neither SSS scores nor the association of SSS with self-rated health, depression, and chronic negative affect differed by mood induction condition, controlling for demographic factors that covary with SSS (e.g., age, gender, education, income). Moreover, chronic negative affect partially explained the relationship between SSS and self-rated health, independent of manipulated mood. Conclusions These findings support the utility of the measurement of SSS, and provide evidence suggesting that chronic negative affect is a likely mediator of the SSS association with global health rather than a confounder. PMID:22329426

Effects of Age at First Childbirth and Other Factors on Central Obesity in Postmenopausal Women: The 2013–2015 Korean National Health and Nutrition Examination Survey

PubMed Central

Lee, Wang Jin; Lee, Joo Ha; Kwag, Byoung Gyu; Chang, Shin Hae; Choi, Yu Jin

2018-01-01

Background Waist circumference is one of the key components of metabolic syndrome. Recent studies demonstrated that the reproductive profile was associated with metabolic syndrome in postmenopausal women. This study focused on the association between central obesity and age at first childbirth. It also considered other factors associated with central obesity in postmenopausal women. Methods This study was based on the 2013–2015 Korean National Health and Nutrition Examination Survey and involved 3,143 naturally postmenopausal women. These women were divided into three groups according to their age at first childbirth: 19 years or younger (n=252), 20–29 years (n=2,695), and 30 years or older (n=196). Multivariate analysis using logistic regression was performed to evaluate the effects of various reproductive factors, including other confounding factors. Results During adjustment for confounding factors, in the early age at first childbirth group, odds ratios (95% confidence intervals) for central obesity decreased. In the final model, younger age at first childbirth was not significantly related to central obesity (waist circumference more than 85 cm) in naturally postmenopausal women after adjusting for other confounding factors. Conclusion Younger age at first childbirth was not significantly associated with central obesity after adjustment for confounding factors. PMID:29788703

Using ecological propensity score to adjust for missing confounders in small area studies.

PubMed

Wang, Yingbo; Pirani, Monica; Hansell, Anna L; Richardson, Sylvia; Blangiardo, Marta

2017-11-09

Small area ecological studies are commonly used in epidemiology to assess the impact of area level risk factors on health outcomes when data are only available in an aggregated form. However, the resulting estimates are often biased due to unmeasured confounders, which typically are not available from the standard administrative registries used for these studies. Extra information on confounders can be provided through external data sets such as surveys or cohorts, where the data are available at the individual level rather than at the area level; however, such data typically lack the geographical coverage of administrative registries. We develop a framework of analysis which combines ecological and individual level data from different sources to provide an adjusted estimate of area level risk factors which is less biased. Our method (i) summarizes all available individual level confounders into an area level scalar variable, which we call ecological propensity score (EPS), (ii) implements a hierarchical structured approach to impute the values of EPS whenever they are missing, and (iii) includes the estimated and imputed EPS into the ecological regression linking the risk factors to the health outcome. Through a simulation study, we show that integrating individual level data into small area analyses via EPS is a promising method to reduce the bias intrinsic in ecological studies due to unmeasured confounders; we also apply the method to a real case study to evaluate the effect of air pollution on coronary heart disease hospital admissions in Greater London. © The Author 2017. Published by Oxford University Press.

Psychosocial Assessment of Self-Harm Patients and Risk of Repeat Presentation: An Instrumental Variable Analysis Using Time of Hospital Presentation.

PubMed

Carroll, Robert; Metcalfe, Chris; Steeg, Sarah; Davies, Neil M; Cooper, Jayne; Kapur, Nav; Gunnell, David

2016-01-01

Clinical guidelines have recommended psychosocial assessment of self-harm patients for years, yet estimates of its impact on the risk of repeat self-harm vary. Assessing the association of psychosocial assessment with risk of repeat self-harm is challenging due to the effects of confounding by indication. We analysed data from a cohort study of 15,113 patients presenting to the emergency departments of three UK hospitals to investigate the association of psychosocial assessment with risk of repeat hospital presentation for self-harm. Time of day of hospital presentation was used as an instrument for psychosocial assessment, attempting to control for confounding by indication. Conventional regression analysis suggested psychosocial assessment was not associated with risk of repeat self-harm within 12 months (Risk Difference (RD) 0.00 95% confidence interval (95%CI) -0.01 to 0.02). In contrast, IV analysis suggested risk of repeat self-harm was reduced by 18% (RD -0.18, 95%CI -0.32 to -0.03) in those patients receiving a psychosocial assessment. However, the instrument of time of day did not remove all potential effects of confounding by indication, suggesting the IV effect estimate may be biased. We found that psychosocial assessments reduce risk of repeat self-harm. This is in-line with other non-randomised studies based on populations in which allocation to assessment was less subject to confounding by indication. However, as our instrument did not fully balance important confounders across time of day, the IV effect estimate should be interpreted with caution.

Correction of confounding bias in non-randomized studies by appropriate weighting.

PubMed

Schmoor, Claudia; Gall, Christine; Stampf, Susanne; Graf, Erika

2011-03-01

In non-randomized studies, the assessment of a causal effect of treatment or exposure on outcome is hampered by possible confounding. Applying multiple regression models including the effects of treatment and covariates on outcome is the well-known classical approach to adjust for confounding. In recent years other approaches have been promoted. One of them is based on the propensity score and considers the effect of possible confounders on treatment as a relevant criterion for adjustment. Another proposal is based on using an instrumental variable. Here inference relies on a factor, the instrument, which affects treatment but is thought to be otherwise unrelated to outcome, so that it mimics randomization. Each of these approaches can basically be interpreted as a simple reweighting scheme, designed to address confounding. The procedures will be compared with respect to their fundamental properties, namely, which bias they aim to eliminate, which effect they aim to estimate, and which parameter is modelled. We will expand our overview of methods for analysis of non-randomized studies to methods for analysis of randomized controlled trials and show that analyses of both study types may target different effects and different parameters. The considerations will be illustrated using a breast cancer study with a so-called Comprehensive Cohort Study design, including a randomized controlled trial and a non-randomized study in the same patient population as sub-cohorts. This design offers ideal opportunities to discuss and illustrate the properties of the different approaches. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A two-stage model in a Bayesian framework to estimate a survival endpoint in the presence of confounding by indication.

PubMed

Bellera, Carine; Proust-Lima, Cécile; Joseph, Lawrence; Richaud, Pierre; Taylor, Jeremy; Sandler, Howard; Hanley, James; Mathoulin-Pélissier, Simone

2018-04-01

Background Biomarker series can indicate disease progression and predict clinical endpoints. When a treatment is prescribed depending on the biomarker, confounding by indication might be introduced if the treatment modifies the marker profile and risk of failure. Objective Our aim was to highlight the flexibility of a two-stage model fitted within a Bayesian Markov Chain Monte Carlo framework. For this purpose, we monitored the prostate-specific antigens in prostate cancer patients treated with external beam radiation therapy. In the presence of rising prostate-specific antigens after external beam radiation therapy, salvage hormone therapy can be prescribed to reduce both the prostate-specific antigens concentration and the risk of clinical failure, an illustration of confounding by indication. We focused on the assessment of the prognostic value of hormone therapy and prostate-specific antigens trajectory on the risk of failure. Methods We used a two-stage model within a Bayesian framework to assess the role of the prostate-specific antigens profile on clinical failure while accounting for a secondary treatment prescribed by indication. We modeled prostate-specific antigens using a hierarchical piecewise linear trajectory with a random changepoint. Residual prostate-specific antigens variability was expressed as a function of prostate-specific antigens concentration. Covariates in the survival model included hormone therapy, baseline characteristics, and individual predictions of the prostate-specific antigens nadir and timing and prostate-specific antigens slopes before and after the nadir as provided by the longitudinal process. Results We showed positive associations between an increased prostate-specific antigens nadir, an earlier changepoint and a steeper post-nadir slope with an increased risk of failure. Importantly, we highlighted a significant benefit of hormone therapy, an effect that was not observed when the prostate-specific antigens trajectory was not accounted for in the survival model. Conclusion Our modeling strategy was particularly flexible and accounted for multiple complex features of longitudinal and survival data, including the presence of a random changepoint and a time-dependent covariate.

Identification of factors involved in medication compliance: incorrect inhaler technique of asthma treatment leads to poor compliance

PubMed Central

Darbà, Josep; Ramírez, Gabriela; Sicras, Antoni; García-Bujalance, Laura; Torvinen, Saku; Sánchez-de la Rosa, Rainel

2016-01-01

Objective To identify the impact of delivery device of inhaled corticosteroids and long-acting β2-agonist (ICS/LABA) on asthma medication compliance, and investigate other factors associated with compliance. Materials and methods We conducted a retrospective and multicenter study based on a review of medical registries of asthmatic patients treated with ICS/LABA combinations (n=2,213) whose medical devices were either dry powder inhalers (DPIs, such as Accuhaler®, Turbuhaler®, and NEXThaler®) or pressurized metered-dose inhalers (pMDI). Medication compliance included persistence outcomes through 18 months and medication possession ratios. Data on potential confounders of treatment compliance such as asthma exacerbations, comorbidities, demographic characteristics, and health care resource utilization were also explored. Results The probability of asthma medication compliance in case of DPIs was lower compared to pMDIs, which suggests that inhaler devices influence inhalation therapies. There were additional confounding factors that were considered as explanatory variables of compliance. A worse measure of airflow obstruction (forced expiration volume in 1 second), comorbidities and general practitioner (GP) consultations more than once per month decreased the probability of compliance. Within comorbidities, alcoholism was positively associated with compliance. Patients of 29–39, 40–50, and 51–61 age groups or suffering from more than two exacerbations during the study period were more likely to comply with their medication regime. The effects of DPIs toward compliance varied with the different DPIs. For instance, Accuhaler® had a greater negative effect on compliance compared to Turbuhaler® and Nexthaler® in cases of patients who suffered exacerbations. We found that GP consultations reduced the probability of medication compliance for patients treated with formoterol/budesonide combination. For retired patients, visiting the GP increased the probability of medication compliance. Conclusion We concluded that inhaler devices influence patients’ compliance for long-term asthma medication. The impact of Accuhaler®, Turbuhaler®, and NEXThaler® on medication compliance was negative. We also identified some confounders of medication compliance such as patient’s age, severity of asthma, comorbidities, and health care costs. PMID:26929605

The Effect of Serum Sodium on Survival in Patients Treated by Peritoneal Dialysis in the United Kingdom.

PubMed

Al-Chidadi, Asmaa; Nitsch, Dorothea; Davenport, Andrew

♦ BACKGROUND: Studies in hemodialysis patients suggest that hyponatremia is associated with increased mortality. However, results from peritoneal dialysis (PD) patients are discordant. We wished to establish whether there was an association between serum sodium and mortality risk in PD patients. ♦ METHODS: We analyzed 3,108 PD patients enrolled at day 90 of renal replacement therapy (RRT) into the UK Renal Registry (UKRR) data base with available serum sodium measurements (in 3 groups: ≤ 137, 138 - 140, ≥ 141 mmol/L) who were then followed up until death or the censoring date (31 December 2012). Analysis used Cox-regression with adjustment for age, sex, year of starting RRT, primary renal disease, serum albumin, smoking, and comorbidities. ♦ RESULTS: Unadjusted mortality rates were 118.6/1,000 person-years (py), 83.4/1,000 py, and 83.5/1,000 py for the lowest, middle, and highest serum sodium tertiles, respectively. After adjustment for covariates, patients in the lowest serum sodium group had almost 50% increased risk of dying compared with those with the highest serum sodium (hazard ratio [HR] 1.49, confidence interval [CI]:1.28 - 1.74), with a graded association between serum sodium and mortality. The association of serum sodium with mortality varied by age (p interaction < 0.001), and whilst this association attenuated after adjustment for confounding variables in the older age groups (55 - 64, and > 65 years), it remained in the younger age group of 18 - 54 years (HR 2.24 [1.36 - 3.70] in the lowest compared with the highest sodium tertile). ♦ CONCLUSIONS: Lower serum sodium concentrations at the start of RRT in PD patients are associated with increased risk of mortality. Whilst this association may well be due to confounding in the older age groups, the persistent strong association between hyponatremia and mortality in the younger age group after adjustment for the available confounders suggests that prospective studies are required to assess whether active intervention to maintain serum sodium changes outcomes. Copyright © 2017 International Society for Peritoneal Dialysis.

Issues and Problems Related to the Research on Teenage Fathers: A Critical Analysis.

ERIC Educational Resources Information Center

Robinson, Bryan E.; Barret, Robert L.

1982-01-01

Research on teenage pregnancies has usually neglected young fathers. Most studies ignore fathers entirely, or use data confused or confounded by biased reporting techniques. Retrospective and post hoc analyses often produce inaccurate conclusions, and subject samples often are unrepresentative. A closer examination of adolescent fathers is…

Small and Large Number Processing in Infants and Toddlers with Williams Syndrome

ERIC Educational Resources Information Center

Van Herwegen, Jo; Ansari, Daniel; Xu, Fei; Karmiloff-Smith, Annette

2008-01-01

Previous studies have suggested that typically developing 6-month-old infants are able to discriminate between small and large numerosities. However, discrimination between small numerosities in young infants is only possible when variables continuous with number (e.g. area or circumference) are confounded. In contrast, large number discrimination…

Using Learning Analytics to Characterize Student Experimentation Strategies in Engineering Design

ERIC Educational Resources Information Center

Vieira, Camilo; Goldstein, Molly Hathaway; Purzer, Senay; Magana, Alejandra J.

2016-01-01

Engineering design is a complex process both for students to participate in and for instructors to assess. Informed designers use the key strategy of conducting experiments as they test ideas to inform next steps. Conversely, beginning designers experiment less, often with confounding variables. These behaviours are not easy to assess in…

Growth and physiology of aspen supplied with different fertilizer addition rates

Treesearch

Mark D. Coleman; Richard E. Dickson; J.G. Isebrands

1998-01-01

Variable internal plant nutrient content may confound plant response to environmental stress. Plant nutrient content may be controlled with relative addition rate techniques in solution culture. However, because raising large numbers of plants in flowing solution culture is difficult. we investieated the feasibility of raisine plants in soil mix using relative...

Neighborhood Frequency Effect in Chinese Word Recognition: Evidence from Naming and Lexical Decision

ERIC Educational Resources Information Center

Li, Meng-Feng; Gao, Xin-Yu; Chou, Tai-Li; Wu, Jei-Tun

2017-01-01

Neighborhood frequency is a crucial variable to know the nature of word recognition. Different from alphabetic scripts, neighborhood frequency in Chinese is usually confounded by component character frequency and neighborhood size. Three experiments were designed to explore the role of the neighborhood frequency effect in Chinese and the stimuli…

Impact of Trauma Work on Social Work Clinicians: Empirical Findings.

ERIC Educational Resources Information Center

Cunningham, Maddy

2003-01-01

Describes a study of social work clinicians working with two types of trauma: sexual abuse and cancer. The effect of clinician's cognitive schemas and the confounding variables of personal history of abuse and years' experience are described. Clinicians who worked primarily with clients who were sexually abused reported more disruptions in…

Maternal Age at Childbirth and Offspring Disruptive Behaviors: Testing the Causal Hypothesis

ERIC Educational Resources Information Center

D'Onofrio, Brian M.; Goodnight, Jackson A.; Van Hulle, Carol A.; Rodgers, Joseph Lee; Rathouz, Paul J.; Waldman, Irwin D.; Lahey, Benjamin B.

2009-01-01

Background: Recent studies suggest that the association between maternal age at childbearing (MAC) and children's disruptive behaviors is the result of family factors that are confounded with both variables, rather than a casual effect of environmental factors specifically related to MAC. These studies, however, relied on restricted samples and…

Long-Term Positive Associations between Music Lessons and IQ

ERIC Educational Resources Information Center

Schellenberg, E. Glenn

2006-01-01

In Study 1 (N = 147), duration of music lessons was correlated positively with IQ and with academic ability among 6-to 11-year-olds, even when potential confounding variables (i.e., family income, parents' education, involvement in nonmusical activities) were held constant. In Study 2 (N = 150), similar but weaker associations between playing…

“Skill of Generalized Additive Model to Detect PM2.5 Health Signal in the Presence of Confounding Variables”

EPA Science Inventory

Summary. Measures of health outcomes are collinear with meteorology and air quality, making analysis of connections between human health and air quality difficult. The purpose of this analysis was to determine time scales and periods shared by the variables of interest (and...

Influences of Phonological Context on Tense Marking in Spanish-English Dual Language Learners

ERIC Educational Resources Information Center

Combiths, Philip N.; Barlow, Jessica A.; Potapova, Irina; Pruitt-Lord, Sonja

2017-01-01

Purpose: The emergence of tense-morpheme marking during language acquisition is highly variable, which confounds the use of tense marking as a diagnostic indicator of language impairment in linguistically diverse populations. In this study, we seek to better understand tense-marking patterns in young bilingual children by comparing phonological…

International Business, Gender, and Training: Preparing for the Global Economy.

ERIC Educational Resources Information Center

Hugenberg, Lawrence W.; And Others

This paper deals with how to train employees in transnational companies to be more "global" in their understanding and awareness of different cultures. The paper defines as "target culture" where the employee or his family will be working and considers as a confounding variable in the international marketplace the role to be…

The Sensitivity of the Right Hemisphere to Contextual Information in Sentences

ERIC Educational Resources Information Center

Gouldthorp, Bethanie; Coney, Jeffrey

2009-01-01

One explanation for the inconsistencies in research examining the sentence comprehension abilities of the right hemisphere (RH) is the presence of confounding variables that have generally served to disadvantage the processing capacities of the RH. As such, the present study aimed to investigate hemispheric differences in the use of message-level…

Learning at the Speed of Light: Deep Learning and Accelerated Online Graduate Courses

ERIC Educational Resources Information Center

Trekles, Anastasia M.

2013-01-01

An increasing number of university programs, particularly at the graduate level, are moving to an accelerated, time-compressed model for online degree offerings. However, the literature revealed that research in distance education effectiveness is still confounded by many variables, including course design and student approach to learning.…

Clomipramine ameliorates adventitious movements and compulsions in prepubertal boys with autistic disorder and severe mental retardation.

PubMed

Brasic, J R; Barnett, J Y; Kaplan, D; Sheitman, B B; Aisemberg, P; Lafargue, R T; Kowalik, S; Clark, A; Tsaltas, M O; Young, J G

1994-07-01

In an open, nonblind clinical trial, clomipramine reduced adventitious movements and compulsions in five previously medicated prepubertal boys with autistic disorder and severe mental retardation. Poorly adapted rating scales, interrater variability, subject heterogeneity, different treatment histories, and environmental stresses confounded the assessment of treatment effects.

The diurnal course of salivary alpha-amylase in nurses: an investigation of potential confounders and associations with stress.

PubMed

Wingenfeld, Katja; Schulz, Michael; Damkroeger, Annika; Philippsen, Christine; Rose, Matthias; Driessen, Martin

2010-09-01

In psychoneuroendocrinology research, salivary measures have become increasingly important. While several studies focus on determinants of salivary cortisol such as age, gender, and gynaecological variables, less research has focused on confounding variables of salivary alpha-amylase (sAA). In a large sample of nurses (N=215) we analyzed the impact of age, gender, intake of oral contraceptives, smoking, coffee consumption as well as psychological parameters, such as work stress and burnout, on basal diurnal sAA release. Saliva was collected at 07:00 h, 11:30 h, 17:30 h, and 20:00 h on a working day during early shift. Only gender could be identified to have an impact on sAA, with females having a more pronounced sAA increase over the course of the day. Whereas depression, anxiety, work stress and burnout were not associated with sAA, a small negative correlation between social difficulties, measured with the Chronic Stress Screening Scale, and sAA could be identified. Copyright (c) 2010 Elsevier B.V. All rights reserved.

Age at immigration and crime in Stockholm using sibling comparisons.

PubMed

Beckley, Amber L

2015-09-01

Past Swedish research has shown that immigrants arriving in the receiving country at an older age are less likely to commit crime than immigrants arriving at a younger age. Segmented assimilation theory argues that the family and neighborhood may be important factors affecting how age at immigration and crime are related to one another. This study used population-based register data on foreign-background males from Stockholm to test the effect of age at immigration on crime. Potential confounding from the family and neighborhood was addressed using variables and modeling strategies. Initial results, using variables to control for confounding, showed that people who immigrated around age 4 were the most likely to be suspected of a crime. When controlling for unmeasured family characteristics, it seemed that a later age at immigration was tied to a lower likelihood of crime, which does not corroborate past research findings. The effect of age at immigration, however, was not statistically significant. The results imply that future research on entire families may be a worthwhile endeavor. Copyright © 2015 Elsevier Inc. All rights reserved.

Peritraumatic tonic immobility is associated with posttraumatic stress symptoms in undergraduate Brazilian students.

PubMed

Portugal, Liana Catarina L; Pereira, Mirtes Garcia; Alves, Rita de Cássia S; Tavares, Gisella; Lobo, Isabela; Rocha-Rego, Vanessa; Marques-Portella, Carla; Mendlowicz, Mauro V; Coutinho, Evandro S; Fiszman, Adriana; Volchan, Eliane; Figueira, Ivan; Oliveira, Letícia de

2012-03-01

Tonic immobility is a defensive reaction occurring under extreme life threats. Patients with posttraumatic stress disorder (PTSD) reporting peritraumatic tonic immobility show the most severe symptoms and a poorer response to treatment. This study investigated the predictive value of tonic immobility for posttraumatic stress symptoms in a non-clinical sample. One hundred and ninety-eight college students exposed to various life threatening events were selected to participate. The Posttraumatic Stress Disorder Checklist - Civilian Version (PCL-C) and tonic immobility questions were used. Linear regression models were fitted to investigate the association between peritraumatic tonic immobility and PCL-C scores. Peritraumatic dissociation, peritraumatic panic reactions, negative affect, gender, type of trauma, and time since trauma were considered as confounding variables. We found significant association between peritraumatic tonic immobility and PTSD symptoms in a non-clinical sample exposed to various traumas, even after regression controlled for confounding variables (β = 1.99, p = 0.017). This automatic reaction under extreme life threatening stress, although adaptive for defense, may have pathological consequences as implied by its association with PTSD symptoms.

The effects of housework on the health of retired older adults: a preliminary investigation from the Tongji-Dongfeng cohort study, China.

PubMed

Wen, Xiaopiao; Liang, Yuan; Zhu, Jiang; Wu, Tangchun

2013-01-01

The aim of the current study was to explore the relationship between housework and health of retired older adults, and to provide new evidences and clues for the effects of housework on health. The data came from the baseline survey of the Tongji-Dongfeng Cohort Study with 25,501 participants. The independent variable was housework including child care, elder care, grocery shopping & cooking, and washing clothes & cleaning house. The dependent variable was self-reported two-week illness. Age, education, marital status, smoking and drinking were used as potential confounding variables. There are gender differences in the four types of housework, with higher prevalence among women than among men. The prevalence of two-week illness in women was higher than that in men. After adjusting for potential confounding variables, the four types of housework had almost no significant effects on two-week illness, except for washing clothes & cleaning house with a negative effect for women (OR = 1.17, 95% CI 1.06-1.29). The association of housework with health, especially of child care, elder care, and grocery shopping & cooking without significance and of washing clothes & cleaning house with significance for women, would provide a valuable clue for in-depth study of housework, namely the effects of housework on health would be subdivided into the dimensions of psychological and social activity besides physical activity, and it may not be suitable to simply classify housework as a kind of exercise.

Comparison of methods for the analysis of relatively simple mediation models.

PubMed

Rijnhart, Judith J M; Twisk, Jos W R; Chinapaw, Mai J M; de Boer, Michiel R; Heymans, Martijn W

2017-09-01

Statistical mediation analysis is an often used method in trials, to unravel the pathways underlying the effect of an intervention on a particular outcome variable. Throughout the years, several methods have been proposed, such as ordinary least square (OLS) regression, structural equation modeling (SEM), and the potential outcomes framework. Most applied researchers do not know that these methods are mathematically equivalent when applied to mediation models with a continuous mediator and outcome variable. Therefore, the aim of this paper was to demonstrate the similarities between OLS regression, SEM, and the potential outcomes framework in three mediation models: 1) a crude model, 2) a confounder-adjusted model, and 3) a model with an interaction term for exposure-mediator interaction. Secondary data analysis of a randomized controlled trial that included 546 schoolchildren. In our data example, the mediator and outcome variable were both continuous. We compared the estimates of the total, direct and indirect effects, proportion mediated, and 95% confidence intervals (CIs) for the indirect effect across OLS regression, SEM, and the potential outcomes framework. OLS regression, SEM, and the potential outcomes framework yielded the same effect estimates in the crude mediation model, the confounder-adjusted mediation model, and the mediation model with an interaction term for exposure-mediator interaction. Since OLS regression, SEM, and the potential outcomes framework yield the same results in three mediation models with a continuous mediator and outcome variable, researchers can continue using the method that is most convenient to them.

High N-Terminal Pro-B-Type Natriuretic Peptide Levels Are Associated with Reduced Heart Rate Variability in Acute Myocardial Infarction

PubMed Central

Lorgis, Luc; Moreau, Daniel; Mock, Laurent; Daumas, Bernadette; Potard, Daniel; Touzery, Claude; Cottin, Yves; Zeller, Marianne

2012-01-01

Aim We investigated the relationships between the autonomic nervous system, as assessed by heart rate variability (HRV) and levels of N-terminal Pro-B-type Natriuretic Peptide (Nt-proBNP) in patients with acute myocardial infarction (MI). Methods and Results The mean of standard deviation of RR intervals (SDNN), the percentage of RR intervals with >50 ms variation (pNN50), square root of mean squared differences of successive RR intervals (rMSSD), and frequency domain parameters (total power (TP), high frequency and low frequency power ratio (LF/HF)) were assessed by 24 h Holter ECG monitoring. 1018 consecutive patients admitted <24 h for an acute MI were included. Plasma Nt-proBNP (Elecsys, Roche) was measured from blood samples taken on admission. The median (IQR) Nt-proBNP level was 681(159–2432) pmol/L. Patients with the highest quartile of Nt-proBNP were older, with higher rate of risk factors and lower ejection fraction. The highest Nt-proBNP quartile group had the lowest SDNN, LF/HF and total power but similar pNN50 and rMSSD levels. Nt-proBNP levels correlated negatively with SDNN (r = −0.19, p<0.001), LF/HF (r = −0.37, p<0.001), and LF (r = −0.29, p<0.001) but not HF (r = −0.043, p = 0.172). Multiple regression analysis showed that plasma propeptide levels remained predictive of LF/HF (B(SE) = −0.065(0.015), p<0.001)), even after adjustment for confounders. Conclusions In conclusion, our population-based study highlights the importance of Nt-proBNP levels to predict decreased HRV after acute MI. PMID:23071500

Variations in thematic mapper spectra of soil related to tillage and crop residue management - Initial evaluation

NASA Technical Reports Server (NTRS)

Seeley, M. W.; Ruschy, D. L.; Linden, D. R.

1983-01-01

A cooperative research project was initiated in 1982 to study differences in thematic mapper spectral characteristics caused by variable tillage and crop residue practices. Initial evaluations of radiometric data suggest that spectral separability of variably tilled soils can be confounded by moisture and weathering effects. Separability of bare tilled soils from those with significant amounts of corn residue is enhanced by wet conditions, but still possible under dry conditions when recent tillage operations have occurred. In addition, thematic mapper data may provide an alternative method to study the radiant energy balance at the soil surface in conjunction with variable tillage systems.

Lung cancer and diesel exhaust: an updated critical review of the occupational epidemiology literature.

PubMed

Gamble, John F; Nicolich, Mark J; Boffetta, Paolo

2012-08-01

A recent review concluded that the evidence from epidemiology studies was indeterminate and that additional studies were required to support the diesel exhaust-lung cancer hypothesis. This updated review includes seven recent studies. Two population-based studies concluded that significant exposure-response (E-R) trends between cumulative diesel exhaust and lung cancer were unlikely to be entirely explained by bias or confounding. Those studies have quality data on life-style risk factors, but do not allow definitive conclusions because of inconsistent E-R trends, qualitative exposure estimates and exposure misclassification (insufficient latency based on job title), and selection bias from low participation rates. Non-definitive results are consistent with the larger body of population studies. An NCI/NIOSH cohort mortality and nested case-control study of non-metal miners have some surrogate-based quantitative diesel exposure estimates (including highest exposure measured as respirable elemental carbon (REC) in the workplace) and smoking histories. The authors concluded that diesel exhaust may cause lung cancer. Nonetheless, the results are non-definitive because the conclusions are based on E-R patterns where high exposures were deleted to achieve significant results, where a posteriori adjustments were made to augment results, and where inappropriate adjustments were made for the "negative confounding" effects of smoking even though current smoking was not associated with diesel exposure and therefore could not be a confounder. Three cohort studies of bus drivers and truck drivers are in effect air pollution studies without estimates of diesel exhaust exposure and so are not sufficient for assessing the lung cancer-diesel exhaust hypothesis. Results from all occupational cohort studies with quantitative estimates of exposure have limitations, including weak and inconsistent E-R associations that could be explained by bias, confounding or chance, exposure misclassification, and often inadequate latency. In sum, the weight of evidence is considered inadequate to confirm the diesel-lung cancer hypothesis.

Factors associated with the choice of general medicine as a career among Japanese medical students.

PubMed

Kawamoto, Ryuichi; Ninomiya, Daisuke; Kasai, Yoshihisa; Kusunoki, Tomo; Ohtsuka, Nobuyuki; Kumagi, Teru; Abe, Masanori

2016-01-01

Background In Japan, there is a shortage of young physicians in various specialties; the present situation of general medicine or family medicine (GM/FM) in particular is risky. The factors influencing the career choice of Japanese medical students are poorly understood. This study aims to identify factors related to choosing GM/FM as a career. Methods The study was designed as a cross-sectional survey. Students at one medical school in Japan filled out a questionnaire. Students were asked to state their intended medical specialty, and they rated the importance of specific individual and occupational aspects using a 4-point likert scale. Factor analysis was performed on the variables. Reliability of the factor scores was estimated using Cronbach's alpha coefficients; biserial correlations between the factors and career choices were calculated. Furthermore, multiple linear regression analysis was performed using career choice (GM/FM vs. others) as the criterion variable and the factors plus demographic characteristics as confounding variables. Results Factor analysis produced six factors that explained future career plans. Medical students in this study had a positive and realistic idea about GM/FM, but only 18.8% of them chose GM/FM first as a career. The significant variables associated with choosing GM/FM first as a career were: 'Admission from hometown' (β=0.189, P=0.001), 'Student preparing for the entrance exam' (β=0.172; P=0.001), 'Intent for rural practice' (β=0.123, P=0.016), and 'Work-life balance' (β=0.126, P=0.013). While significant variables that were negatively associated with choosing GM/FM were 'Presence of medical relatives' (β=-0.107, P=0.037) and 'Scientific orientation' (β=-0.125, P=0.013). Conclusions Strategies have been suggested, such as recruiting medical students with significant variables that were associated with choosing GM/FM first as a career. By engaging students early in their choice of career, we may be able to increase enthusiasm for this specialty.

"A Bayesian sensitivity analysis to evaluate the impact of unmeasured confounding with external data: a real world comparative effectiveness study in osteoporosis".

PubMed

Zhang, Xiang; Faries, Douglas E; Boytsov, Natalie; Stamey, James D; Seaman, John W

2016-09-01

Observational studies are frequently used to assess the effectiveness of medical interventions in routine clinical practice. However, the use of observational data for comparative effectiveness is challenged by selection bias and the potential of unmeasured confounding. This is especially problematic for analyses using a health care administrative database, in which key clinical measures are often not available. This paper provides an approach to conducting a sensitivity analyses to investigate the impact of unmeasured confounding in observational studies. In a real world osteoporosis comparative effectiveness study, the bone mineral density (BMD) score, an important predictor of fracture risk and a factor in the selection of osteoporosis treatments, is unavailable in the data base and lack of baseline BMD could potentially lead to significant selection bias. We implemented Bayesian twin-regression models, which simultaneously model both the observed outcome and the unobserved unmeasured confounder, using information from external sources. A sensitivity analysis was also conducted to assess the robustness of our conclusions to changes in such external data. The use of Bayesian modeling in this study suggests that the lack of baseline BMD did have a strong impact on the analysis, reversing the direction of the estimated effect (odds ratio of fracture incidence at 24 months: 0.40 vs. 1.36, with/without adjusting for unmeasured baseline BMD). The Bayesian twin-regression models provide a flexible sensitivity analysis tool to quantitatively assess the impact of unmeasured confounding in observational studies. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Periodontitis is associated with diabetic retinopathy in non-obese adults.

PubMed

Song, Su Jeong; Lee, Seong-Su; Han, Kyungdo; Park, Jun-Beom

2017-04-01

Patients with diabetes retinopathy appear to show increased susceptibility to periodontal disease. This study was performed to assess the relationship between periodontitis and the prevalence of diabetic retinopathy in a large probability sample of the Korean population. A subgroup analysis was performed using body mass index <25 kg/m 2 as the criterion to evaluate the effect of obesity on this relationship. This study is based on data from the Korean National Health and Nutrition Examination Survey of the Korean population, conducted between 2008 and 2010. The presence of diabetic retinopathy in relation to demographic variables and anthropometric characteristics of the participants is presented as means with their standard errors. The presence of periodontitis and presence of retinopathy categorized by body mass index (<25 and ≥25 kg/m 2 ) were evaluated. Multiple logistic regression analyses were used to assess the associations between periodontitis and diabetic retinopathy after adjustment with variables, including age, sex, smoking, drinking, exercise, hypertension, metabolic syndrome, HbA1c, and duration of diabetes mellitus. There was a statistically significant increase in the prevalence of periodontitis in individuals who had proliferative diabetic retinopathy. The odds ratios [95% confidence intervals] of prevalence of diabetic retinopathy were 1.193 [0.757-1.881] for the whole population after adjustments with confounding factors. Subgroup analysis after adjustments with confounding factors showed that the odds ratios [95% confidence intervals] of prevalence were 2.206 [1.114-4.366] and 0.588 [0.326-1.061] among participants with body mass index <25 kg/m 2 and body mass index 37 ≥25 kg/m 2 , respectively. The diabetic retinopathy was positively associated with the presence of periodontitis in non-obese diabetic Korean adults after adjustment with confounding variables. Our findings suggest that when a periodontist finds the presence of periodontitis in non-obese diabetic patients, timely evaluation of the patient's ophthalmic evaluation should be 44 recommended.

Assessment of the number of eye symptoms and the impact of some confounding variables for office staff in non-air-conditioned buildings.

PubMed

Doughty, Michael J; Blades, Kenneth A; Ibrahim, Nassim

2002-03-01

The goal of this study was both to assess the frequency of self-reported eye symptoms for employees in a non-air-conditioned office building complex, and to specifically assess whether confounding variables (contact lens wear, medicines use, and provoking stimuli) had a discernible impact on the characteristics of this reporting. A questionnaire was distributed, in the winter months, to office employees in a building complex within a city-located University site, consisting of non-air-conditioned rooms with some mechanical ventilation. The questionnaire asked respondents to identify any eye symptoms experienced (foreign body sensation, soreness, dryness, grittiness, itchiness, stinging, intense burning), the frequency of their occurrence, details of any conditions provoking eye symptoms (such as changes in the microenvironment), their medication use and if they were contact lens wearers. The proportion of respondents for various categories was calculated, along with the total number of symptoms. If 'eye irritation' is considered as reporting any symptoms experienced at any time, then 63% of 292 respondents (median age 42.5 years) reported an average of 1.83 symptoms. However, the identification of contact lens wearers, medication use (especially for seasonal allergies) and provoking stimuli reduced this prevalence to just 29% (with the average number of symptoms being 1.51). If the frequency of experiencing symptoms was also taken into account (never, sometimes, often, and constantly), then only 12.3% of the respondents indicated symptoms often or constantly, i.e. could be considered to have significant symptoms. In all categories, men were more likely to report eye symptoms compared with women. The results confirm that office employees are likely to have some ocular symptoms, but that even a simple consideration of possible confounding variables can greatly change the reported prevalence of eye irritation that might be specifically associated with the workplace environment.

Does the frequency of anxiety and depressive disorders differ between diagnostic subtypes of anorexia nervosa and bulimia?

PubMed

Godart, Nathalie; Berthoz, Sylvie; Rein, Zoé; Perdereau, Fabienne; Lang, François; Venisse, Jean-Luc; Halfon, Olivier; Bizouard, Pierre; Loas, Gwénolé; Corcos, Maurice; Jeammet, Philippe; Flament, Martine; Curt, Florence

2006-12-01

The objective of the present work is to determine whether the prevalence of depressive and anxiety disorders varies in subgroups of eating disorders (ED) according to age, ED duration, mode of care provision, and body mass index (BMI). Using the Mini International Neuropsychiatric Interview (MINI), the frequency of anxiety and depressive disorders was evaluated in 271 ED participants. Their prevalence was compared in subgroups of anorexics (AN-R and AN-BN) and bulimics (BN), both before and after controlling for potential confounding variables. Current or lifetime comorbidity of anxiety and depressive disorders did not differ between AN-R and AN-BN groups. Social phobia, panic disorders, and obsessive-compulsive disorder (OCD) were significantly more frequent in AN-BN and AN-R groups. Panic disorder was more frequent in the BN group. Several confounding factors, in particular those identified in the present study, may explain previous conflicting results on the frequency of anxiety and depressive disorders in ED. Nevertheless, the study confirmed that OCD is more frequent in AN, even after controlling for confounding factors. Copyright 2006 by Wiley Periodicals, Inc.

Population pharmacodynamic modelling of midazolam induced sedation in terminally ill adult patients

PubMed Central

de Winter, Brenda C. M.; Masman, Anniek D.; van Dijk, Monique; Baar, Frans P. M.; Tibboel, Dick; Koch, Birgit C. P.; van Gelder, Teun; Mathot, Ron A. A.

2017-01-01

Aims Midazolam is the drug of choice for palliative sedation and is titrated to achieve the desired level of sedation. A previous pharmacokinetic (PK) study showed that variability between patients could be partly explained by renal function and inflammatory status. The goal of this study was to combine this PK information with pharmacodynamic (PD) data, to evaluate the variability in response to midazolam and to find clinically relevant covariates that may predict PD response. Method A population PD analysis using nonlinear mixed effect models was performed with data from 43 terminally ill patients. PK profiles were predicted by a previously described PK model and depth of sedation was measured using the Ramsay sedation score. Patient and disease characteristics were evaluated as possible covariates. The final model was evaluated using a visual predictive check. Results The effect of midazolam on the sedation level was best described by a differential odds model including a baseline probability, Emax model and interindividual variability on the overall effect. The EC50 value was 68.7 μg l–1 for a Ramsay score of 3–5 and 117.1 μg l–1 for a Ramsay score of 6. Comedication with haloperidol was the only significant covariate. The visual predictive check of the final model showed good model predictability. Conclusion We were able to describe the clinical response to midazolam accurately. As expected, there was large variability in response to midazolam. The use of haloperidol was associated with a lower probability of sedation. This may be a result of confounding by indication, as haloperidol was used to treat delirium, and deliria has been linked to a more difficult sedation procedure. PMID:28960387

Frailty among rural elderly adults

PubMed Central

2014-01-01

Background This study aimed to estimate the prevalence and associated factors related to frailty, by Fried criteria, in the elderly population in a rural area in the Andes Mountains, and to analyze the relationship of these with comorbidity and disability. Methods A cross-sectional study was undertaken involving 1878 participants 60 years of age and older. The frailty syndrome was diagnosed based on the Fried criteria (weakness, low speed, low physical activity, exhaustion, and weight loss). Variables were grouped as theoretical domains and, along with other potential confounders, were placed into five categories: (a) demographic and socioeconomic status, (b) health status, (c) self-reported functional status, (d) physical performance-based measures, and (e) psychosocial factors. Chi-square, ANOVA, and multinomial logistic regression analyses were used to test the prognostic value of frailty for the outcomes of interest. Results The prevalence of frailty was 12.2%. Factors associated with frailty were age, gender, health status variables that included self-perceived health and number of chronic conditions, functional covariate variables that included disability in activities in daily living (ADL), disabilities in instrumental ADL, chair stand time, and psychosocial variables that included depressive symptoms and cognitive impairment. Higher comorbidity and disability was found in frail elderly people. Only a subset of frail elderly people (10%) reported no disease or disability. Conclusions A relevant number of elderly persons living in rural areas in the Andes Mountains are frail. The prevalence of frailty is similar to that reported in other populations in the Latin American region. Our results support the use of modified Cardiovascular Health Study criteria to measure frailty in communities other than urban settings. Frailty in this study was strongly associated with comorbidities, and frailty and comorbidity predicted disability. PMID:24405584

Supervisor Autonomy and Considerate Leadership Style are Associated with Supervisors' Likelihood to Accommodate Back Injured Workers.

PubMed

McGuire, Connor; Kristman, Vicki L; Shaw, William; Williams-Whitt, Kelly; Reguly, Paula; Soklaridis, Sophie

2015-09-01

To determine the association between supervisors' leadership style and autonomy and supervisors' likelihood of supporting job accommodations for back-injured workers. A cross-sectional study of supervisors from Canadian and US employers was conducted using a web-based, self-report questionnaire that included a case vignette of a back-injured worker. Autonomy and two dimensions of leadership style (considerate and initiating structure) were included as exposures. The outcome, supervisors' likeliness to support job accommodation, was measured with the Job Accommodation Scale (JAS). We conducted univariate analyses of all variables and bivariate analyses of the JAS score with each exposure and potential confounding factor. We used multivariable generalized linear models to control for confounding factors. A total of 796 supervisors participated. Considerate leadership style (β = .012; 95% CI .009-.016) and autonomy (β = .066; 95% CI .025-.11) were positively associated with supervisors' likelihood to accommodate after adjusting for appropriate confounding factors. An initiating structure leadership style was not significantly associated with supervisors' likelihood to accommodate (β = .0018; 95% CI -.0026 to .0061) after adjusting for appropriate confounders. Autonomy and a considerate leadership style were positively associated with supervisors' likelihood to accommodate a back-injured worker. Providing supervisors with more autonomy over decisions of accommodation and developing their considerate leadership style may aid in increasing work accommodation for back-injured workers and preventing prolonged work disability.

Assessing moderated mediation in linear models requires fewer confounding assumptions than assessing mediation.

PubMed

Loeys, Tom; Talloen, Wouter; Goubert, Liesbet; Moerkerke, Beatrijs; Vansteelandt, Stijn

2016-11-01

It is well known from the mediation analysis literature that the identification of direct and indirect effects relies on strong no unmeasured confounding assumptions of no unmeasured confounding. Even in randomized studies the mediator may still be correlated with unobserved prognostic variables that affect the outcome, in which case the mediator's role in the causal process may not be inferred without bias. In the behavioural and social science literature very little attention has been given so far to the causal assumptions required for moderated mediation analysis. In this paper we focus on the index for moderated mediation, which measures by how much the mediated effect is larger or smaller for varying levels of the moderator. We show that in linear models this index can be estimated without bias in the presence of unmeasured common causes of the moderator, mediator and outcome under certain conditions. Importantly, one can thus use the test for moderated mediation to support evidence for mediation under less stringent confounding conditions. We illustrate our findings with data from a randomized experiment assessing the impact of being primed with social deception upon observer responses to others' pain, and from an observational study of individuals who ended a romantic relationship assessing the effect of attachment anxiety during the relationship on mental distress 2 years after the break-up. © 2016 The British Psychological Society.

Evaluation of the use of oseltamivir prophylaxis in the control of influenza outbreaks in long-term care facilities in Alberta, Canada: a retrospective provincial database analysis

PubMed Central

Ye, Ming; Jacobs, Angela; Khan, Muhammad Naeem; Jaipaul, Joy; Oda, Joanna; Johnson, Marcia; Doroshenko, Alexander

2016-01-01

Objectives To evaluate the impact of oseltamivir prophylaxis in the management and control of influenza outbreaks in long-term care facilities in Alberta, Canada. Setting and participants Long-term care facilities where 127 influenza outbreaks were reported to public health authorities in Alberta, Canada, during two influenza seasons from 2013 to 2015. Design and outcome measures Using routinely collected surveillance and administrative data, we examined the association between decision-making time for oseltamivir recommendation as prophylaxis strategy for influenza outbreaks in long-term care facilities (explanatory variable) and the duration of an influenza outbreak, the postprophylaxis risk of influenza-like illness and hospitalisation among residents of long-term care facilities in Alberta (outcome variables) using multivariable linear and Poisson regression models. Results Oseltamivir prophylaxis decision-making time was positively associated with the postintervention duration of an outbreak, with a 1-day delay in making decision on oseltamivir prophylaxis associated with 2.22 (95% CI 1.37 to 3.06) more days of the duration of an outbreak after controlling for potential confounding effect of the number of residents at risk at intervention, outbreak progression time, prevalence of influenza-like illness during outbreak progression, facility location, presence of mixed strain and based on optimal timing of oseltamivir prophylaxis. Although not statistically significant, a 1-day delay in making decision on oseltamivir prophylaxis was associated with a 5% (95% CI −1% to 11%) increase in the postintervention risk of influenza-like illness, and a 6% (95% CI −8% to 22%) increase in the postintervention risk of hospitalisation after controlling for the same potential confounders. Conclusions Our study demonstrated benefits of using oseltamivir prophylaxis to shorten the duration of influenza outbreaks; however, there were no significant differences in the influenza-like illness and hospitalisation risk occurring after the intervention. Surveillance data may offer means of rapid evaluation of oseltamivir prophylaxis in long-term care facilities as a public health measure. PMID:27381211

High Mammographic Density in Long-Term Night-Shift Workers: DDM-Spain/Var-DDM.

PubMed

Pedraza-Flechas, Ana María; Lope, Virginia; Sánchez-Contador, Carmen; Santamariña, Carmen; Pedraz-Pingarrón, Carmen; Moreo, Pilar; Ederra, María; Miranda-García, Josefa; Vidal, Carmen; Llobet, Rafael; Aragonés, Nuria; Salas-Trejo, Dolores; Pollán, Marina; Pérez-Gómez, Beatriz

2017-06-01

Background: Night-shift work (NSW) has been suggested as a possible cause of breast cancer, and its association with mammographic density (MD), one of the strongest risk factors for breast cancer, has been scarcely addressed. This study examined NSW and MD in Spanish women. Methods: The study covered 2,752 women aged 45-68 years recruited in 2007-2008 in 7 population-based public breast cancer screening centers, which included 243 women who had performed NSW for at least one year. Occupational data and information on potential confounders were collected by personal interview. Two trained radiologist estimated the percentage of MD assisted by a validated semiautomatic computer tool (DM-scan). Multivariable mixed linear regression models with random screening center-specific intercepts were fitted using log-transformed percentage of MD as the dependent variable and adjusting by known confounding variables. Results: Having ever worked in NSW was not associated with MD [Formula: see text]:0.96; 95% confidence interval (CI), 0.86-1.06]. However, the adjusted geometric mean of the percentage of MD in women with NSW for more than 15 years was 25% higher than that of those without NSW history (MD >15 years :20.7% vs. MD never :16.5%;[Formula: see text]:1.25; 95% CI,1.01-1.54). This association was mainly observed in postmenopausal participants ([Formula: see text]:1.28; 95% CI, 1.00-1.64). Among NSW-exposed women, those with ≤2 night-shifts per week had higher MD than those with 5 to 7 nightshifts per week ([Formula: see text]:1.42; 95% CI, 1.10-1.84). Conclusions: Performing NSW was associated with higher MD only in women with more than 15 years of cumulated exposure. These findings warrant replication in futures studies. Impact: Our findings suggest that MD could play a role in the pathway between long-term NSW and breast cancer. Cancer Epidemiol Biomarkers Prev; 26(6); 905-13. ©2017 AACR . ©2017 American Association for Cancer Research.

Instrumental variable applications using nursing home prescribing preferences in comparative effectiveness research.

PubMed

Huybrechts, Krista F; Gerhard, Tobias; Franklin, Jessica M; Levin, Raisa; Crystal, Stephen; Schneeweiss, Sebastian

2014-08-01

Nursing home residents are of particular interest for comparative effectiveness research given their susceptibility to adverse treatment effects and systematic exclusion from trials. However, the risk of residual confounding because of unmeasured markers of declining health using conventional analytic methods is high. We evaluated the validity of instrumental variable (IV) methods based on nursing home prescribing preference to mitigate such confounding, using psychotropic medications to manage behavioral problems in dementia as a case study. A cohort using linked data from Medicaid, Medicare, Minimum Data Set, and Online Survey, Certification and Reporting for 2001-2004 was established. Dual-eligible patients ≥65 years who initiated psychotropic medication use after admission were selected. Nursing home prescribing preference was characterized using mixed-effects logistic regression models. The plausibility of IV assumptions was explored, and the association between psychotropic medication class and 180-day mortality was estimated. High-prescribing and low-prescribing nursing homes differed by a factor of 2. Each preference-based IV measure described a substantial proportion of variation in psychotropic medication choice (β(IV → treatment): 0.22-0.36). Measured patient characteristics were well balanced across patient groups based on instrument status (52% average reduction in Mahalanobis distance). There was no evidence that instrument status was associated with markers of nursing home quality of care. Findings indicate that IV analyses using nursing home prescribing preference may be a useful approach in comparative effectiveness studies, and should extend naturally to analyses including untreated comparison groups, which are of great scientific interest but subject to even stronger confounding. Copyright © 2014 John Wiley & Sons, Ltd.

Temperature variability during delirium in ICU patients: an observational study.

PubMed

van der Kooi, Arendina W; Kappen, Teus H; Raijmakers, Rosa J; Zaal, Irene J; Slooter, Arjen J C

2013-01-01

Delirium is an acute disturbance of consciousness and cognition. It is a common disorder in the intensive care unit (ICU) and associated with impaired long-term outcome. Despite its frequency and impact, delirium is poorly recognized by ICU-physicians and -nurses using delirium screening tools. A completely new approach to detect delirium is to use monitoring of physiological alterations. Temperature variability, a measure for temperature regulation, could be an interesting component to monitor delirium, but whether temperature regulation is different during ICU delirium has not yet been investigated. The aim of this study was to investigate whether ICU delirium is related to temperature variability. Furthermore, we investigated whether ICU delirium is related to absolute body temperature. We included patients who experienced both delirium and delirium free days during ICU stay, based on the Confusion Assessment method for the ICU conducted by a research- physician or -nurse, in combination with inspection of medical records. We excluded patients with conditions affecting thermal regulation or therapies affecting body temperature. Daily temperature variability was determined by computing the mean absolute second derivative of the temperature signal. Temperature variability (primary outcome) and absolute body temperature (secondary outcome) were compared between delirium- and non-delirium days with a linear mixed model and adjusted for daily mean Richmond Agitation and Sedation Scale scores and daily maximum Sequential Organ Failure Assessment scores. Temperature variability was increased during delirium-days compared to days without delirium (β(unadjuste)d=0.007, 95% confidence interval (CI)=0.004 to 0.011, p<0.001). Adjustment for confounders did not alter this result (β(adjusted)=0.005, 95% CI=0.002 to 0.008, p<0.001). Delirium was not associated with absolute body temperature (β(unadjusted)=-0.03, 95% CI=-0.17 to 0.10, p=0.61). This did not change after adjusting for confounders (β(adjusted)=-0.03, 95% CI=-0.17 to 0.10, p=0.63). Our study suggests that temperature variability is increased during ICU delirium.

The Effects of Combat Exposure on Reenlistment and Attrition

DTIC Science & Technology

2011-03-01

confounded with the job assignment, but the amount of bias should be minimal given that most people would stay within their trained specialty. C...SECURITY CLASSIFICATION OF ABSTRACT Unclassified 20. LIMITATION OF ABSTRACT UU NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed...CONCLUSIONS ............................................................................................87 B. STUDY LIMITATIONS

The Relation between Binge Drinking and Academic Performance: Considering the Mediating Effects of Academic Involvement

ERIC Educational Resources Information Center

An, Brian P.; Loes, Chad N.; Trolian, Teniell L.

2017-01-01

Using longitudinal data from multiple institutions, we focused on the relation between binge drinking and academic performance. Binge drinking exerts a negative influence on grade point average, even after accounting for a host of precollege confounding variables. Furthermore, the number of times a student binge drinks in college is less…

Stress-Disorder Symptoms in Vietnam and Korean War Veterans: A Commentary on Thienes-Hontos, Watson, and Kucala.

ERIC Educational Resources Information Center

Caroll, Edward

1983-01-01

Reviews a study which found that symptoms associated with posttraumatic stress disorder (PTSD) are neither unique to or common among Vietnam veteran psychiatric patients or their Korean war counterparts. Questions choice of study sample, confounding variables, and source of data. A rebuttal by the original author is included. (WAS)

Root disease and other unforeseen variables that confound restoration efforts

Treesearch

William J. Otrosina; Shi-Jean S. Sung; Stanley J. Zarnoch; Brian T. Sullivan; Charles H. Walkinshaw

2002-01-01

Unanticipated disease problems thwarting restoration efforts can emerge in forest ecosystems. An example is the longleaf pine (Pinus palustris Mill.) ecosystem. This species once occupied nearly 30 million ha but now its range is reduced to approximately 1.5 million ha. Restoring longleaf pine to many sites in its former range is an important goal...

Gender Bias in the Diagnosis of a Geriatric Standardized Patient: A Potential Confounding Variable

ERIC Educational Resources Information Center

Lewis, Roya; Lamdan, Ruth M.; Wald, David; Curtis, Michael

2006-01-01

Background: Gender bias has been reported in the diagnosis and treatment of patients with a variety of illnesses. In the context of our 10-station fourth year Objective Structured Clinical Evaluation, we queried whether this could influence diagnosis in a geriatric case. Case writers hypothesized that, due to this bias, the female standardized…

Typing Speed as a Confounding Variable and the Measurement of Quality in Divergent Thinking

ERIC Educational Resources Information Center

Forthmann, Boris; Holling, Heinz; Çelik, Pinar; Storme, Martin; Lubart, Todd

2017-01-01

The need to control for writing or typing speed when assessing divergent-thinking performance has been recognized since the early '90s. An even longer tradition in divergent-thinking research has the issue of scoring the responses for quality. This research addressed both issues within structural equation modeling. Three dimensions of…

Implementing the undergraduate mini-CEX: a tailored approach at Southampton University.

PubMed

Hill, Faith; Kendall, Kathleen; Galbraith, Kevin; Crossley, Jim

2009-04-01

The mini-clinical evaluation exercise (mini-CEX) is widely used in the UK to assess clinical competence, but there is little evidence regarding its implementation in the undergraduate setting. This study aimed to estimate the validity and reliability of the undergraduate mini-CEX and discuss the challenges involved in its implementation. A total of 3499 mini-CEX forms were completed. Validity was assessed by estimating associations between mini-CEX score and a number of external variables, examining the internal structure of the instrument, checking competency domain response rates and profiles against expectations, and by qualitative evaluation of stakeholder interviews. Reliability was evaluated by overall reliability coefficient (R), estimation of the standard error of measurement (SEM), and from stakeholders' perceptions. Variance component analysis examined the contribution of relevant factors to students' scores. Validity was threatened by various confounding variables, including: examiner status; case complexity; attachment specialty; patient gender, and case focus. Factor analysis suggested that competency domains reflect a single latent variable. Maximum reliability can be achieved by aggregating scores over 15 encounters (R = 0.73; 95% confidence interval [CI] +/- 0.28 based on a 6-point assessment scale). Examiner stringency contributed 29% of score variation and student attachment aptitude 13%. Stakeholder interviews revealed staff development needs but the majority perceived the mini-CEX as more reliable and valid than the previous long case. The mini-CEX has good overall utility for assessing aspects of the clinical encounter in an undergraduate setting. Strengths include fidelity, wide sampling, perceived validity, and formative observation and feedback. Reliability is limited by variable examiner stringency, and validity by confounding variables, but these should be viewed within the context of overall assessment strategies.

Concentrations of Water-Soluble Vitamins in Blood and Urinary Excretion in Patients with Diabetes Mellitus.

PubMed

Iwakawa, Hiromi; Nakamura, Yasuyuki; Fukui, Tomiho; Fukuwatari, Tsutomu; Ugi, Satoshi; Maegawa, Hiroshi; Doi, Yukio; Shibata, Katsumi

2016-01-01

We examined the concentrations of water-soluble vitamins in blood and urinary excretion of 22 patients with type 2 diabetes mellitus (type 2DM) and 20 healthy control participants. Macronutrient and vitamin intakes of type 2DM subjects were measured using a weighed food record method. Control participants consumed a semipurified diet for eight days. Multiple linear regression models were used to determine whether significant differences existed in vitamin concentrations in blood independent of age, sex, and other confounding factors. Concentrations of vitamins B2, B6, C, niacin, and folate in blood were significantly lower in type 2DM subjects than in controls, independent of confounding factors. Renal clearances of vitamins B6, C, niacin, and folate were significantly higher in type 2DM subjects than in controls. In conclusion, concentrations of vitamins B2, B6, C, niacin, and folate in blood were significantly lower in type 2DM subjects than in controls, independent of confounding factors; based on the evidence of increased urinary clearance of these vitamins, the lower levels were likely due to impaired reabsorption processes.

Residential proximity to electromagnetic field sources and birth weight: Minimizing residual confounding using multiple imputation and propensity score matching.

PubMed

de Vocht, Frank; Lee, Brian

2014-08-01

Studies have suggested that residential exposure to extremely low frequency (50 Hz) electromagnetic fields (ELF-EMF) from high voltage cables, overhead power lines, electricity substations or towers are associated with reduced birth weight and may be associated with adverse birth outcomes or even miscarriages. We previously conducted a study of 140,356 singleton live births between 2004 and 2008 in Northwest England, which suggested that close residential proximity (≤ 50 m) to ELF-EMF sources was associated with reduced average birth weight of 212 g (95%CI: -395 to -29 g) but not with statistically significant increased risks for other adverse perinatal outcomes. However, the cohort was limited by missing data for most potentially confounding variables including maternal smoking during pregnancy, which was only available for a small subgroup, while also residual confounding could not be excluded. This study, using the same cohort, was conducted to minimize the effects of these problems using multiple imputation to address missing data and propensity score matching to minimize residual confounding. Missing data were imputed using multiple imputation using chained equations to generate five datasets. For each dataset 115 exposed women (residing ≤ 50 m from a residential ELF-EMF source) were propensity score matched to 1150 unexposed women. After doubly robust confounder adjustment, close proximity to a residential ELF-EMF source remained associated with a reduction in birth weight of -116 g (95% confidence interval: -224:-7 g). No effect was found for proximity ≤ 100 m compared to women living further away. These results indicate that although the effect size was about half of the effect previously reported, close maternal residential proximity to sources of ELF-EMF remained associated with suboptimal fetal growth. Copyright © 2014 Elsevier Ltd. All rights reserved.

Good research practices for comparative effectiveness research: approaches to mitigate bias and confounding in the design of nonrandomized studies of treatment effects using secondary data sources: the International Society for Pharmacoeconomics and Outcomes Research Good Research Practices for Retrospective Database Analysis Task Force Report--Part II.

PubMed

Cox, Emily; Martin, Bradley C; Van Staa, Tjeerd; Garbe, Edeltraut; Siebert, Uwe; Johnson, Michael L

2009-01-01

The goal of comparative effectiveness analysis is to examine the relationship between two variables, treatment, or exposure and effectiveness or outcome. Unlike data obtained through randomized controlled trials, researchers face greater challenges with causal inference with observational studies. Recognizing these challenges, a task force was formed to develop a guidance document on methodological approaches to addresses these biases. The task force was commissioned and a Chair was selected by the International Society for Pharmacoeconomics and Outcomes Research Board of Directors in October 2007. This report, the second of three reported in this issue of the Journal, discusses the inherent biases when using secondary data sources for comparative effectiveness analysis and provides methodological recommendations to help mitigate these biases. The task force report provides recommendations and tools for researchers to mitigate threats to validity from bias and confounding in measurement of exposure and outcome. Recommendations on design of study included: the need for data analysis plan with causal diagrams; detailed attention to classification bias in definition of exposure and clinical outcome; careful and appropriate use of restriction; extreme care to identify and control for confounding factors, including time-dependent confounding. Design of nonrandomized studies of comparative effectiveness face several daunting issues, including measurement of exposure and outcome challenged by misclassification and confounding. Use of causal diagrams and restriction are two techniques that can improve the theoretical basis for analyzing treatment effects in study populations of more homogeneity, with reduced loss of generalizability.

Availability and structure of primary medical care services and population health and health care indicators in England

PubMed Central

Gulliford, Martin C; Jack, Ruth H; Adams, Geoffrey; Ukoumunne, Obioha C

2004-01-01

Background It has been proposed that greater availability of primary medical care practitioners (GPs) contributes to better population health. We evaluated whether measures of the supply and structure of primary medical services are associated with health and health care indicators after adjusting for confounding. Methods Data for the supply and structure of primary medical services and the characteristics of registered patients were analysed for 99 health authorities in England in 1999. Health and health care indicators as dependent variables included standardised mortality ratios (SMR), standardised hospital admission rates, and conceptions under the age of 18 years. Linear regression analyses were adjusted for Townsend score, proportion of ethnic minorities and proportion of social class IV/ V. Results Higher proportions of registered rural patients and patients ≥ 75 years were associated with lower Townsend deprivation scores, with larger partnership sizes and with better health outcomes. A unit increase in partnership size was associated with a 4.2 (95% confidence interval 1.7 to 6.7) unit decrease in SMR for all-cause mortality at 15–64 years (P = 0.001). A 10% increase in single-handed practices was associated with a 1.5 (0.2 to 2.9) unit increase in SMR (P = 0.027). After additional adjustment for percent of rural and elderly patients, partnership size and proportion of single-handed practices, GP supply was not associated with SMR (-2.8, -6.9 to 1.3, P = 0.183). Conclusions After adjusting for confounding with health needs of populations, mortality is weakly associated with the degree of organisation of practices as represented by the partnership size but not with the supply of GPs. PMID:15193157

Rates of Initial Virological Suppression and Subsequent Virological Failure After Initiating Highly Active Antiretroviral Therapy: The Impact of Aboriginal Ethnicity and Injection Drug Use

PubMed Central

Martin, L.J.; Houston, S.; Yasui, Y.; Wild, T.C.; Saunders, L.D.

2010-01-01

Objectives: To compare rates of initial virological suppression and subsequent virological failure by Aboriginal ethnicity after starting highly active antiretroviral therapy (HAART). Methods: We conducted a retrospective cohort study of antiretroviral-naïve HIV-patients starting HAART in January 1999-June 2005 (baseline), followed until December 31, 2005 in Alberta, Canada. We compared the odds of achieving initial virological suppression (viral load <500 copies/mL) by Aboriginal ethnicity using logistic regression and, among those achieving suppression, rates of virological failure (the first of two consecutive viral loads > 1000 copies/mL) by Aboriginal ethnicity using cumulative incidence curves and Cox proportional hazards models. Sex, injection drug use as an HIV exposure category (IDU), baseline age, CD4 cell count, viral load, calendar year, and HAART regimen were considered as potential confounders. Results: Of 461 study patients, 37% were Aboriginal and 48% were IDUs; 71% achieved initial virological suppression and were followed for 730.4 person-years. After adjusting for confounding variables, compared to non-Aboriginals with other exposures, the odds of achieving initial virological suppression were lower for Aboriginal IDUs (odds ratio (OR)=0.33, 95% CI=0.19-0.60, p=0.0002), non-Aboriginal IDUs (OR=0.30, 95% CI=0.15-0.60, p=0.0006), and Aboriginals with other exposures (OR=0.38, 95% CI=0.21-0.67, p=0.0009). Among those achieving suppression, Aboriginals experienced higher virological failure rates ≥1 year after suppression (hazard ratio=3.35, 95% CI=1.68-6.65, p=0.0006). Conclusions: Future research should investigate adherence among Aboriginals and IDUs treated with HAART and explore their treatment experiences to assess ways to improve outcomes. PMID:21187007

Associations Between Sleep Duration Patterns and Behavioral/Cognitive Functioning at School Entry

PubMed Central

Touchette, Évelyne; Petit, Dominique; Séguin, Jean R.; Boivin, Michel; Tremblay, Richard E.; Montplaisir, Jacques Y.

2007-01-01

Objective: The aim of the study was to investigate the associations between longitudinal sleep duration patterns and behavioral/cognitive functioning at school entry. Design, Setting, and Participants: Hyperactivity-impulsivity (HI), inattention, and daytime sleepiness scores were measured by questionnaire at 6 years of age in a sample of births from 1997 to 1998 in a Canadian province (N=1492). The Peabody Picture Vocabulary Test - Revised (PPVT-R) was administered at 5 years of age and the Block Design subtest (WISC-III) was administered at 6 years of age. Sleep duration was reported yearly by the children's mothers from age 2.5 to 6 years. A group-based semiparametric mixture model was used to estimate developmental patterns of sleep duration. The relationships between sleep duration patterns and both behavioral items and neurodevelopmental tasks were tested using weighted multivariate logistic regression models to control for potentially confounding psychosocial factors. Results: Four sleep duration patterns were identified: short persistent (6.0%), short increasing (4.8%),10-hour persistent (50.3%), and 11-hour persistent (38.9%). The association of short sleep duration patterns with high HI scores (P=0.001), low PPVT-R performance (P=0.002), and low Block Design subtest performance (P=0.004) remained significant after adjusting for potentially confounding variables. Conclusions: Shortened sleep duration, especially before the age of 41 months, is associated with externalizing problems such as HI and lower cognitive performance on neurodevelopmental tests. Results highlight the importance of giving a child the opportunity to sleep at least 10 hours per night throughout early childhood. Citation: Touchette E; Petit D; Séguin JR; Boivin M; Tremblay RE; Montplaisir JY. Associations between sleep duration patterns and behavioral/cognitive functioning at school entry. SLEEP 2007;30(9):1213-1219. PMID:17910393

Systematic review of the quality and generalizability of studies on the effects of opioids on driving and cognitive/psychomotor performance.

PubMed

Mailis-Gagnon, Angela; Lakha, Shehnaz Fatima; Furlan, Andrea; Nicholson, Keith; Yegneswaran, Balaji; Sabatowski, Rainer

2012-07-01

The effect of opioids on driving performance has been much debated. Driving is a complex task requiring integration of psychomotor, cognitive, motor and decision-making skills, visual-spatial abilities, divided attention, and behavioral and emotional control. The objective of this systematic review was to assess the quality of studies and to revisit the concept that patients on stable opioids are safe to drive as it applies to everyday practice. We searched MEDLINE, EMBASE, PSYCinfo, CENTRAL, TRANSPORT, CINAHL, reference lists of retrieved articles and narrative reviews, for studies on chronic cancer and noncancer pain patients on opioids, tested by driving, driving simulator, or cognitive/psychomotor tests. Methodological quality was assessed with Methodological Index for Nonrandomized Studies, cognitive/psychomotor tests were appraised regarding their sensitivity and validation, and whether confounding variables potentially affecting the study conclusions were recorded. The results were analyzed both quantitatively and qualitatively. We included 35 studies (2044 patients, 1994 controls), 9% of the studies were of poor, 54% of fair, and 37% of high quality; 3 quarters of the studies used high sensitivity cognitive tests. Amount and dose of opioids varied largely in many studies. Mean number of possible but unreported confounders was 2.2 (range, 0 to 4), relating to failure of the studies to mention co-prescriptions with psychotropic effects, pain severity, sleep disorder or daytime somnolence, and/or significant depressive or anxiety-related problems. The commonly held concept that "chronic pain patients on stable opioids are safe to drive" cannot be generalized to all such patients in everyday practice, but may be applicable only to a subset who meet certain criteria.

Witness of Intimate Partner Violence in Childhood and Perpetration of Intimate Partner Violence in Adulthood

PubMed Central

Roberts, Andrea L.; Gilman, Stephen E.; Fitzmaurice, Garrett; Decker, Michele R.; Koenen, Karestan C.

2011-01-01

Background At least half a million women are victims of intimate partner violence in the United States annually, resulting in substantial harm. However, the etiology of violence to intimate partners is not well understood. Witnessing such violence in childhood has been proposed as a principal cause of adulthood perpetration, yet it remains unknown whether the association between witnessing intimate partner violence and adulthood perpetration is causal. Method We conducted a propensity-score analysis of intimate partner violence perpetration to determine whether childhood witnessing is associated with perpetration in adulthood, independent of a wide range of potential confounding variables, and therefore might be a causal factor. We used data from 14,564 U.S. men ages 20 and older from the 2004–2005 wave of the National Epidemiologic Survey on Alcohol and Related Conditions. Results Nearly 4% of men reported violent behavior toward an intimate partner in the past year. In unadjusted models, we found a strong association between childhood witnessing of intimate partner violence and adulthood perpetration (for witnessing any intimate partner violence, risk ratio [RR] = 2.6 [95% confidence interval = 2.1–3.2]; for witnessing frequent or serious violence, 3.0 [2.3–3.9]). In propensity-score models, the association was substantially attenuated (for witnessing any intimate partner violence, adjusted RR = 1.6 [1.2–2.0]; for witnessing frequent or serious violence, 1.6 [1.2–2.3]). Conclusions Men who witness intimate partner violence in childhood are more likely to commit such acts in adulthood, compared with men who are otherwise similar with respect to a large range of potential confounders. Etiological models of intimate partner violence perpetration should consider a constellation of childhood factors. PMID:20811285

Voxel-wise motion artifacts in population-level whole-brain connectivity analysis of resting-state FMRI.

PubMed

Spisák, Tamás; Jakab, András; Kis, Sándor A; Opposits, Gábor; Aranyi, Csaba; Berényi, Ervin; Emri, Miklós

2014-01-01

Functional Magnetic Resonance Imaging (fMRI) based brain connectivity analysis maps the functional networks of the brain by estimating the degree of synchronous neuronal activity between brain regions. Recent studies have demonstrated that "resting-state" fMRI-based brain connectivity conclusions may be erroneous when motion artifacts have a differential effect on fMRI BOLD signals for between group comparisons. A potential explanation could be that in-scanner displacement, due to rotational components, is not spatially constant in the whole brain. However, this localized nature of motion artifacts is poorly understood and is rarely considered in brain connectivity studies. In this study, we initially demonstrate the local correspondence between head displacement and the changes in the resting-state fMRI BOLD signal. Than, we investigate how connectivity strength is affected by the population-level variation in the spatial pattern of regional displacement. We introduce Regional Displacement Interaction (RDI), a new covariate parameter set for second-level connectivity analysis and demonstrate its effectiveness in reducing motion related confounds in comparisons of groups with different voxel-vise displacement pattern and preprocessed using various nuisance regression methods. The effect of using RDI as second-level covariate is than demonstrated in autism-related group comparisons. The relationship between the proposed method and some of the prevailing subject-level nuisance regression techniques is evaluated. Our results show that, depending on experimental design, treating in-scanner head motion as a global confound may not be appropriate. The degree of displacement is highly variable among various brain regions, both within and between subjects. These regional differences bias correlation-based measures of brain connectivity. The inclusion of the proposed second-level covariate into the analysis successfully reduces artifactual motion-related group differences and preserves real neuronal differences, as demonstrated by the autism-related comparisons.

Relationship Between Circulating Concentrations of Thyrotropin, Free Thyroxine, and Free Triiodothyronine and 9-Year Mortality in Euthyroid Elderly Subjects

PubMed Central

Ceresini, Graziano; Marina, Michela; Lauretani, Fulvio; Maggio, Marcello; Bandinelli, Stefania; Ceda, Gian Paolo; Ferrucci, Luigi

2015-01-01

Objectives Thyroid dysfunction in the elderly is associated with adverse clinical outcomes, with mortality being associated with low TSH. However, it is still unknown whether variability of thyroid function test within the reference range is associated with mortality in older adults. We studied the association between plasma levels of TSH, free T3 (FT3), and free T4 (FT4), and all-cause mortality in older adults who had all three hormones within the normal range. Design Longitudinal study Setting Community-based Participants Total of 815 euthyroid participants of the InCHIANTI study, aged 65 years or older Measurements All subjects had TSH, FT3, and FT4 within the reference range at baseline. Plasma TSH, FT3 and FT4 were predictors and 9-year all-cause mortality was the outcome. Cox proportional hazards models adjusted for confounders were used to examine the relationship between quartiles of TSH, FT3, and FT4 and all-cause mortality over 9 years of follow-up. Results During the follow-up (mean persons-years 8643.74 [min-max, 35.36-16985.00]), 181 deaths occurred (22.2%). Participants with TSH in the lower quartile had higher mortality than the rest of the population. After adjusting for multiple confounders, participants with TSH in the lowest quartile (Hazard Ratio: 2.22; 95% Confidence Interval: 1.19–4.22) had significantly higher all-cause mortality than those with TSH in the highest quartile. Neither FT3 nor FT4 were associated with mortality. Conclusions In euthyroid elderly subjects, normal-low TSH represents an independent risk factor for all-cause mortality. PMID:27000328

Rimonabant’s Reductive Effects on High Densities of Food Reinforcement, but not Palatability, in Lean and Obese Zucker Rats

PubMed Central

Buckley, Jessica Lynn; Rasmussen, Erin B.

2014-01-01

Rationale Cannabinoid antagonists purportedly have greater effects in reducing the intake of highly palatable food compared to less palatable food. However, this assertion is based on free-feeding studies in which the amount of palatable food eaten under baseline conditions is often confounded with other variables, such as unequal access to both food options and differences in qualitative features of the foods. Objective We attempted to reduce these confounds by using a model of choice that programmed the delivery rates of sucrose and carrot-flavored pellets. Methods Lever-pressing of ten lean (Fa/Fa or Fa/fa) and ten obese (fa/fa) Zucker rats was placed under three conditions in which programmed ratios for food pellets on two levers were 5:1, 1:1, and 1:5. In Phase 1, responses on the two levers produced one type of pellet (sucrose or carrot); in Phase 2, responses on one lever produced sucrose pellets and on the other lever produced carrot pellets. After responses stabilized under each food ratio, acute doses of rimonabant (0, 3, and 10 mg/kg) were administered before experimental sessions. The number of reinforcers and responses earned per session under each ratio and from each lever was compared. Results and Conclusions Rimonabant reduced reinforcers in 1:5 and 5:1 food ratios in Phase 1, and across all ratios in Phase 2. Rimonabant reduced sucrose and carrot-flavored pellet consumption similarly; rimonabant did not affect bias toward sucrose, but increased sensitivity to amount differences in lean rats. This suggests that relative amount of food, not palatability, may be an important behavioral mechanism in the effects of rimonabant. PMID:24398820

Body mass index is not a clinically meaningful predictor of patient reported outcomes of primary hip replacement surgery: prospective cohort study

PubMed Central

Judge, Andy; Batra, Rajbir N; Thomas, Geraint; Beard, David; Javaid, M Kassim; Murray, David; Dieppe, Paul A; Dreinhoefer, Karsten; Peter-Guenther, Klaus; Field, Richard; Cooper, Cyrus; Arden, Nigel K

2014-01-01

Objectives To describe whether body mass index (BMI) is a clinically meaningful predictor of patient reported outcomes following primary total hip replacement (THR) surgery Design Combined data from prospective cohort studies. We obtained information from four cohorts of patients receiving primary THR for osteoarthritis: Exeter Primary Outcomes Study (n=1431); EUROHIP (n=1327); Elective Orthopaedic Centre (n=2832); and St. Helier (n=787). The exposure of interest was pre-operative BMI. Confounding variables included: age, sex, SF-36 mental health, comorbidities, fixed flexion, analgesic use, college education, OA in other joints, expectation of less pain, radiographic K&L grade, ASA grade, years of hip pain. The primary outcome was the Oxford Hip Score (OHS). Regression models describe the association of BMI on outcome adjusting for all confounders. Results For a 5-unit increase in BMI, the attained 12-month OHS decreases by 0.78 points 95%CI (0.27 to 1.28), p-value 0.001. Compared to people of normal BMI (20 to 25), those in the obese class II (BMI 35 to 40) would have a 12-month OHS that is 2.34 points lower. Although statistically significant this effect is small and not clinically meaningful in contrast to the substantial change in OHS seen across all BMI groupings. In obese class II patients achieved a 22.2 point change in OHS following surgery. Conclusions Patients achieved substantial change in OHS after THR across all BMI categories, which greatly outweighs the small difference in attained post-operative score. The findings suggest BMI should not present a barrier to access THR in terms of PROMs. PMID:24418679

Self-reported body silhouette trajectories across the lifespan and excessive daytime sleepiness in adulthood: a retrospective analysis. The Paris Prospective Study III

PubMed Central

Tafflet, Muriel; Charles, Marie-Aline; Thomas, Frédérique; Boutouyrie, Pierre; Guibout, Catherine; Haba-Rubio, José; Périer, Marie Cécile; Pannier, Bruno; Marques-Vidal, Pedro; Jouven, Xavier; Empana, Jean-Philippe

2018-01-01

Objectives Excessive daytime sleepiness (EDS) is a common sleep complaint in the population and is increasingly recognised as deleterious for health. Simple and sensitive tools allowing identifying individuals at greater risk of EDS would be of public health importance. Hence, we determined trajectories of body silhouette from early childhood to adulthood and evaluated their association with EDS in adulthood. Design A retrospective analysis in a prospective community-based study. Participants 6820 men and women self-reported their silhouette at ages 8, 15, 25, 35 and 45 using the body silhouettes proposed by Stunkard et al. EDS was defined by an Epworth Sleepiness Scale score ≥11. Main outcome measure Presence of EDS in adulthood. Results The study population comprised 6820 participants (mean age 59.8 years, 61.1% men). Five distinct body silhouettes trajectories over the lifespan were identified: 31.9% ‘lean stable’, 11.1% ‘lean increase’, 16.1% ‘lean-marked increase’, 32.5% ‘moderate stable’ and 8.4% ‘heavy stable’. Subjects with a ‘heavy-stable’ trajectory (OR 1.24, 95% CI 0.94 to 1.62) and those with a ‘lean-marked increase’ trajectory (OR 1.46, 95% CI 1.18 to 1.81) were more likely to have EDS when compared with the ‘lean-stable’ group after adjusting for confounding. Further adjustment for birth weight strengthened the magnitude of the ORs. Conclusion Increasing body silhouette and to a lesser extent constantly high body silhouette trajectory from childhood to adulthood are associated with increased likelihood of EDS, independently of major confounding variables. Trial registration number NCT00741728; Pre-results. PMID:29593025

The Relationship between Intake of Dairy Products and Polycystic Ovary Syndrome in Women Who Referred to Isfahan University of Medical Science Clinics in 2013

PubMed Central

Rajaeieh, Golnaz; Marasi, Mohamadreza; Shahshahan, Zahra; Hassanbeigi, Fatemmeh; Safavi, Seied Morteza

2014-01-01

Background: Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in reproductive women. Nearly 10% of young women in this period involved. Although factors such as Insulin Resistance, hyper insulinemia, obesity and dietary are suggested to be associated with PCOS, cause of PCOS is not completely understood. Dairy products (a key component of the usual diet) of participants can also affect the factors of this disease and may have beneficial effects on treatment of PCOS. However, research in this area is scarce. The purpose of this study was to evaluate the relationship between dairy products consumption and PCOS. Methods: This descriptive cross-sectional study of 400 women was conducted in Shahid Beheshti Hospital of Isfahan University of Medical Science, Iran. Dietary intake was evaluated by validated food frequency questionnaire. Other variables such as ovarian disease, inherited predisposition, age at menarche, physical activity and history of other diseases were evaluated using questionnaire. Data analysis was performed by a logistic regression test using SPSS software version 15 Predictive analytics software and solutions. Results: There were a significant association between PCOS and ovarian disease (P < 0.001), age (P < 0.001) and using medication (P = 0.001). Body mass index (BMI) was inversely associated with PCOS, but it was not significant (P = 0.068). There was a significant direct relationship between milk consumption and risk of PCOS after adjusting for confounding factors (P = 0.028). Conclusions: The findings of this study indicated that ovarian disease and medication use is directly linked to PCOS. Dairy consumption was not significantly correlated with PCOS. However, after adjustment for confounders, there was an direct relationship between milk consumption and risk of PCOS. PMID:25013687

Poor Sleep Quality, Antepartum Depression and Suicidal Ideation among Pregnant Women

PubMed Central

Gelaye, Bizu; Addae, Gifty; Neway, Beemnet; Larrabure-Torrealva, Gloria T.; Qiu, Chunfang; Stoner, Lee; Fernandez, Miguel Angel Luque; Sanchez, Sixto E.; Williams, Michelle A.

2016-01-01

Objective To evaluate the independent and combined associations of maternal self-reported poor sleep quality and antepartum depression with suicidal ideation during the third trimester Methods A cross-sectional study was conducted among 1,298 pregnant women (between 24 and 28 gestational weeks) attending prenatal clinics in Lima, Peru. Antepartum depression and suicidal ideation were assessed using the Patient Health Questionnaire-9 (PHQ-9). The Pittsburgh Sleep Quality Index (PSQI) questionnaire was used to assess sleep quality. Multivariate logistical regression procedures were used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) after adjusting for putative confounders. Results Approximately, 17% of women were classified as having poor sleep quality (defined using the recommended criteria of PSQI global score of >5 vs. ≤5). Further, the prevalence of antepartum depression and suicidal ideation were 10.3% and 8.5%, respectively in this cohort. After adjusting for confounders including depression, poor sleep quality was associated with a 2.81-fold increased odds of suicidal ideation (OR=2.81; 95% CI 1.78–4.45). When assessed as a continuous variable, each 1-unit increase in the global PSQI score resulted in a 28% increase in odds for suicidal ideation, even after adjusting for depression (OR=1.28; 95% CI 1.15–1.41). The odds of suicidal ideation was particularly high among depressed women with poor sleep quality (OR=13.56 95% CI 7.53–24.41) as compared with women without either risk factor. Limitations This cross-sectional study utilized self-reported data. Causality cannot be inferred, and results may not be fully generalizable. Conclusion Poor sleep quality, even after adjusting for depression, is associated with antepartum suicidal ideation. Our findings support the need to explore sleep-focused interventions for pregnant women. PMID:27930912

Effect of Exposure to Air Pollution on Placental Weight in Isfahan-Iran.

PubMed

Ghasemi-Tehrani, Hatav; Fallah, Setare; Mozafarian, Nafiseh; Miranzadeh, Sareh; Sadeghi, Shokooh; Azidhak, Azam

2017-06-01

Objective: To determine the effect of Air Quality Index (AQI) in the first trimester of pregnancy on birth weight, placental weight, and the ratio of placental weight to the birth weight (pw-bw) in Isfahan. Materials and methods: This cross-sectional study was done on 312 consecutive pregnant women in Beheshti Hospital in Isfahan city in 2013. Information on air pollution was received from the Environmental department of Isfahan. Average exposure to air pollution in the first trimester of pregnancy was calculated for eachpregnant woman. In order to compare quantitative and qualitative variables, analysis of variance (ANOVA), and chi-square were applied. After that, the multiple linear regression analysis was used to assess the association the Air Quality Index (AQI) on birth weight, placental weight and the ratio of pw-bw. Potential confounders including age, baby gender, smoking of husband, maternal BMI, maternal occupation, and education and mother's residential area were considered. A statistical significant association were considered for P-value less than 0.05. Results: The findings showed that there is inverse relationship between exposure to air pollution and placental weight in the first trimester of pregnancy after controlling potential confounders (β = -2.57, p-value = 0.008). The inverse relationship between air pollution and the ratio of pw-bw was found. (β = -0.001, p-value = 0.002). Conclusion: The results of this study suggest that air pollution is associated with newborns' health which in turn is a warning alarm for considering some actions in both sides of reducing the air pollution and teaching the pregnant women about the adverse effects of air pollution on the pregnancy outcomes.

Paternal education status significantly influences infants’ measles vaccination uptake, independent of maternal education status

PubMed Central

2012-01-01

Background Despite increased funding of measles vaccination programs by national governments and international aid agencies, structural factors encumber attainment of childhood measles immunisation to levels which may guarantee herd immunity. One of such factors is parental education status. Research on the links between parental education and vaccination has typically focused on the influence of maternal education status. This study aims to demonstrate the independent influence of paternal education status on measles immunisation. Methods Comparable nationally representative survey data were obtained from six countries with the highest numbers of children missing the measles vaccine in 2008. Logistic regression analysis was applied to examine the influence of paternal education on uptake of the first dose of measles vaccination, independent of maternal education, whilst controlling for confounding factors such as respondent’s age, urban/rural residence, province/state of residence, religion, wealth and occupation. Results The results of the analysis show that even if a mother is illiterate, having a father with an education of Secondary (high school) schooling and above is statistically significant and positively correlated with the likelihood of a child being vaccinated for measles, in the six countries analysed. Paternal education of secondary or higher level was significantly and independently correlated with measles immunisation uptake after controlling for all potential confounders. Conclusions The influence of paternal education status on measles immunisation uptake was investigated and found to be statistically significant in six nations with the biggest gaps in measles immunisation coverage in 2008. This study underscores the imperative of utilising both maternal and paternal education as screening variables to identify children at risk of missing measles vaccination prospectively. PMID:22568861

Gang membership and substance use: guilt as a gendered causal pathway

PubMed Central

Coffman, Donna L.; Melde, Chris; Esbensen, Finn-Aage

2014-01-01

Objectives We examine whether anticipated guilt for substance use is a gendered mechanism underlying the noted enhancement effect of gang membership on illegal drug use. We also demonstrate a method for making stronger causal inferences when assessing mediation in the presence of moderation and time-varying confounding. Methods We estimate a series of inverse propensity weighted models to obtain unbiased estimates of mediation in the presence of confounding of the exposure (i.e., gang membership) and mediator (i.e., anticipated guilt) using three waves of data from a multi-site panel study of a law-related education program for youth (N=1,113). Results The onset of gang membership significantly decreased anticipated substance use guilt among both male and female respondents. This reduction was significantly associated with increased frequency of substance use only for female respondents, however, suggesting that gender moderates the mechanism through which gang membership influences substance use. Conclusions Criminologists are often concerned with identifying causal pathways for antisocial and/or delinquent behavior, but confounders of the exposure, mediator, and outcome often interfere with efforts to assess mediation. Many new approaches have been proposed for strengthening causal inference for mediation effects. After controlling for confounding using inverse propensity weighting, our results suggest that interventions aimed at reducing substance use by current and former female gang members should focus on the normative aspects of these behaviors. PMID:26190954

Comparing a marginal structural model with a Cox proportional hazard model to estimate the effect of time-dependent drug use in observational studies: statin use for primary prevention of cardiovascular disease as an example from the Rotterdam Study.

PubMed

de Keyser, Catherine E; Leening, Maarten J G; Romio, Silvana A; Jukema, J Wouter; Hofman, Albert; Ikram, M Arfan; Franco, Oscar H; Stijnen, Theo; Stricker, Bruno H

2014-11-01

When studying the causal effect of drug use in observational data, marginal structural modeling (MSM) can be used to adjust for time-dependent confounders that are affected by previous treatment. The objective of this study was to compare traditional Cox proportional hazard models (with and without time-dependent covariates) with MSM to study causal effects of time-dependent drug use. The example of primary prevention of cardiovascular disease (CVD) with statins was examined using up to 17.7 years of follow-up from 4,654 participants of the observational prospective population-based Rotterdam Study. In the MSM model, the weight was based on measurements of established cardiovascular risk factors and co-morbidity. In general, we could not demonstrate important differences in results from the Cox models and MSM. Results from analysis on duration of statin use suggested that substantial residual confounding by indication was not accounted for during the period shortly after statin initiation. In conclusion, although on theoretical grounds MSM is an elegant technique, lack of data on the precise time-dependent confounders, such as indication of treatment or other considerations of the prescribing physician jeopardizes the calculation of valid weights. Confounding remains a hurdle in observational effectiveness research on preventive drugs with a multitude of prescription determinants.

Physical Activity and Bone Health in Schoolchildren: The Mediating Role of Fitness and Body Fat

PubMed Central

Torres-Costoso, Ana; Gracia-Marco, Luis; Sánchez-López, Mairena; Notario-Pacheco, Blanca; Arias-Palencia, Natalia; Martínez-Vizcaíno, Vicente

2015-01-01

Background The relationship between physical activity (PA) and bone health is well known, although the role of percent body fat (%BF) and fitness as confounders or mediators in this relationship remains uncertain. Objective To examine whether the association between PA and bone mineral content (BMC) is mediated by %BF and cardiorespiratory fitness (CRF). Methods In this cross sectional study, BMC, total %BF (by DXA), vigorous PA (VPA), CRF, age and height were measured in 132 schoolchildren (62 boys, aged 8–11 years). ANCOVA was used to test differences in BMC by %BF, CRF and VPA, controlling for different sets of confounders. Simple mediation analyses and serial multiple mediation analyses were fitted to examine whether the relationship between PA and BMC is mediated by %BF and fitness. Results Children with high %BF had higher total body BMC than their peers after controlling for all sets of confounders. Children with good CRF or VPA had significantly less total body BMC after controlling for age and sex but in children with good CRF this inverse relation disappeared after adjusting by %BF. %BF and CRF both act as a full mediator in the association between VPA and BMC, after inclusion of the potential confounders in the models. Conclusion Fitness and %BF seem to have a mediator role on the relationship between physical activity and bone mass. PMID:25915941

Advanced statistical methods to study the effects of gastric tube and non-invasive ventilation on functional decline and survival in amyotrophic lateral sclerosis.

PubMed

Atassi, Nazem; Cudkowicz, Merit E; Schoenfeld, David A

2011-07-01

A few studies suggest that non-invasive ventilation (1) and gastric tube (G-tube) may have a positive impact on survival but the effect on functional decline is unclear. Confounding by indication may have produced biased estimates of the benefit seen in some of these retrospective studies. The objective of this study was to evaluate the effects of G-tube and NIV on survival and functional decline using advanced statistical models that adjust for confounding by indications. A database of 331 subjects enrolled in previous clinical trials in ALS was available for analysis. Marginal structural models (MSM) were used to compare the mortality hazards and ALSFRS-R slopes between treatment and non-treatment groups, after adjusting for confounding by indication. Results showed that the placement of a G-tube was associated with an additional 1.42 units/month decline in the ALSFRS-R slope (p < 0.0001) and increased mortality hazard of 0.28 (p = 0.02). The use of NIV had no significant effect on ALSFRS-R decline or mortality. In conclusion, marginal structural models can be used to adjust for confounding by indication in retrospective ALS studies. G-tube placement could be followed by a faster rate of functional decline and increased mortality. Our results may suffer from some of the limitations of retrospective analyses.

Insomnia Severity, Subjective Sleep Quality, and Risk for Obstructive Sleep Apnea in Veterans With Gulf War Illness.

PubMed

Chao, Linda L; Abadjian, Linda R; Esparza, Iva L; Reeb, Rosemary

2016-09-01

Despite the fact that sleep disturbances are common in veterans with Gulf War Illness (GWI), there has been a paucity of published sleep studies in this veteran population to date. Therefore, the present study examined subjective sleep quality (assessed with the Pittsburgh Sleep Quality Index), insomnia severity (assessed with the Insomnia Severity Index), and risk for obstructive sleep apnea (assessed with the STOP questionnaire) in 98 Gulf War veterans. Veterans with GWI, defined either by the Kansas or Centers for Disease Control and Prevention criteria, had greater risk for obstructive sleep apnea (i.e., higher STOP scores) than veterans without GWI. This difference persisted even after accounting for potentially confounding demographic (e.g., age, gender) and clinical variables. Veterans with GWI, defined by either the Kansas or Centers for Disease Control and Prevention criteria, also had significantly greater insomnia severity and poorer sleep quality than veterans without GWI (p < 0.05), even after accounting for potentially confounding variables. Furthermore, there were significant, positive correlations between insomnia severity, subjective sleep quality, and GWI symptom severity (p ≤ 0.01). In stepwise linear regression models, insomnia severity significantly predicted GWI status over and above demographic and clinical variables. Together these findings provide good rationale for treating sleep disturbances in the management of GWI. Reprint & Copyright © 2016 Association of Military Surgeons of the U.S.

Coping strategies and quality of life in caregivers of dependent elderly relatives.

PubMed

Rodríguez-Pérez, Margarita; Abreu-Sánchez, Ana; Rojas-Ocaña, María Jesús; Del-Pino-Casado, Rafael

2017-04-14

Despite the importance of coping in caregiving, there are few studies on the relationship between coping and quality of life in caregivers of the frail dependent elderly. Thus, this study aims to analyze the relationship between coping strategies and quality of life dimensions in primary caregivers of dependent elderly relatives. A cross-sectional study was conducted from 86 caregivers. Predictive variables were coping strategies (problem-focused, emotion-focused, socially-supported, and dysfunctional); dependent variables were quality of life dimensions (psychological, physical, relational, and environmental); and potential confounding variables were age, gender, perceived health and burden of caregiver, and functional capacity of care receiver. Correlation coefficients were calculated and multiple linear regression analysis was performed. After controlling for potential confounders, dysfunctional coping was related to worse quality of life in the psychological dimension, while emotion-focused and socially-supported coping were related to superior psychological and environmental dimensions of quality of life. The physical and relational dimensions of quality of life were not related to coping strategies. 1) it is important to consider coping strategies in the assessment of primary caregivers of dependent elderly relatives; 2) the quality of life of caregivers is related to their coping strategies, 3) their quality of life can be worsened by avoidance-type coping, and 4) their quality of life can be improved by active emotion-focused coping and socially-supported coping.

Covariate selection with group lasso and doubly robust estimation of causal effects

PubMed Central

Koch, Brandon; Vock, David M.; Wolfson, Julian

2017-01-01

Summary The efficiency of doubly robust estimators of the average causal effect (ACE) of a treatment can be improved by including in the treatment and outcome models only those covariates which are related to both treatment and outcome (i.e., confounders) or related only to the outcome. However, it is often challenging to identify such covariates among the large number that may be measured in a given study. In this paper, we propose GLiDeR (Group Lasso and Doubly Robust Estimation), a novel variable selection technique for identifying confounders and predictors of outcome using an adaptive group lasso approach that simultaneously performs coefficient selection, regularization, and estimation across the treatment and outcome models. The selected variables and corresponding coefficient estimates are used in a standard doubly robust ACE estimator. We provide asymptotic results showing that, for a broad class of data generating mechanisms, GLiDeR yields a consistent estimator of the ACE when either the outcome or treatment model is correctly specified. A comprehensive simulation study shows that GLiDeR is more efficient than doubly robust methods using standard variable selection techniques and has substantial computational advantages over a recently proposed doubly robust Bayesian model averaging method. We illustrate our method by estimating the causal treatment effect of bilateral versus single-lung transplant on forced expiratory volume in one year after transplant using an observational registry. PMID:28636276

Covariate selection with group lasso and doubly robust estimation of causal effects.

PubMed

Koch, Brandon; Vock, David M; Wolfson, Julian

2018-03-01

The efficiency of doubly robust estimators of the average causal effect (ACE) of a treatment can be improved by including in the treatment and outcome models only those covariates which are related to both treatment and outcome (i.e., confounders) or related only to the outcome. However, it is often challenging to identify such covariates among the large number that may be measured in a given study. In this article, we propose GLiDeR (Group Lasso and Doubly Robust Estimation), a novel variable selection technique for identifying confounders and predictors of outcome using an adaptive group lasso approach that simultaneously performs coefficient selection, regularization, and estimation across the treatment and outcome models. The selected variables and corresponding coefficient estimates are used in a standard doubly robust ACE estimator. We provide asymptotic results showing that, for a broad class of data generating mechanisms, GLiDeR yields a consistent estimator of the ACE when either the outcome or treatment model is correctly specified. A comprehensive simulation study shows that GLiDeR is more efficient than doubly robust methods using standard variable selection techniques and has substantial computational advantages over a recently proposed doubly robust Bayesian model averaging method. We illustrate our method by estimating the causal treatment effect of bilateral versus single-lung transplant on forced expiratory volume in one year after transplant using an observational registry. © 2017, The International Biometric Society.

Complex Causal Process Diagrams for Analyzing the Health Impacts of Policy Interventions

PubMed Central

Joffe, Michael; Mindell, Jennifer

2006-01-01

Causal diagrams are rigorous tools for controlling confounding. They also can be used to describe complex causal systems, which is done routinely in communicable disease epidemiology. The use of change diagrams has advantages over static diagrams, because change diagrams are more tractable, relate better to interventions, and have clearer interpretations. Causal diagrams are a useful basis for modeling. They make assumptions explicit, provide a framework for analysis, generate testable predictions, explore the effects of interventions, and identify data gaps. Causal diagrams can be used to integrate different types of information and to facilitate communication both among public health experts and between public health experts and experts in other fields. Causal diagrams allow the use of instrumental variables, which can help control confounding and reverse causation. PMID:16449586

Effect of Placenta Previa on Preeclampsia

PubMed Central

Ying, Hao; Lu, Yi; Dong, Yi-Nuo; Wang, De-Fen

2016-01-01

Background The correlation between gestational hypertension-preeclampsia (GH-PE) and placenta previa (PP) is controversial. Specifically, it is unknown whether placenta previa has any effect on the various types of preeclampsia (PE), and the role PP with concurrent placenta accreta (PA) play in the occurrence of GH-PE are not well understood. Objective The aim of this study was to identify the effects of PP on GH, mild and severe preeclampsia (MPE and SPE), and early- and late-onset preeclampsia (EPE and LPE). Another aim of the study was to determine if concurrent PA impacts the relationship between PP and GH-PE. Methods A retrospective single-center study of 1,058 patients having singleton pregnancies with PP was performed, and 2,116 pregnant women were randomly included as controls. These cases were collected from a tertiary hospital and met the inclusion criteria for the study. Clinical information, including PP and the gestational age at the onset of GH-PE were collected. Binary and multiple logistic regression analyses were conducted after the confounding variables were controlled to assess the effects of PP on different types of GH-PE. Results There were 155 patients with GH-PE in the two groups. The incidences of GH-PE in the PP group and the control group were 2.5% (26/1058) and 6.1% (129/2116), respectively (P = 0.000). Binary and multiple regression analyses were conducted after controlling for confounding variables. Compared to the control group, in the PP group, the risk of GH-PE was reduced significantly by 78% (AOR: 0.216; 95% CI: 0.135–0.345); the risks of GH and PE were reduced by 55% (AOR: 0.451; 95% CI: 0.233–0.873) and 86% (AOR: 0.141; 95% CI: 0.073–0.271), respectively; the risks of MPE and SPE were reduced by 73% (AOR: 0.269; 95% CI: 0.087–0828) and 88% (AOR: 0.123; 95% CI: 0.055–0.279), respectively; and the risks of EPE and LPE were reduced by 95% (AOR: 0.047; 95% CI: 0.012–0.190) and 67% (AOR: 0.330; 95% CI: 0.153–0.715), respectively. The incidence of concurrent PA in women with PP was 5.86%; PP with PA did not significantly further reduce the incidence of GH-PE compared with PP without PA (1.64% vs. 2.51%, P>0.05). Binary logistic regression analyses were conducted after controlling for confounding variables, compared with the non-PP + GH-PE group, and the AOR of FGR in the non-PP + non-GH-PE group was 0.206 (0.124–0.342). Compared with the PP + GH-PE group, the AOR of FGR in the PP + non-GH-PE group was 0.430 (0.123–1.500). Conclusion PP is not only associated with a significant reduction in the incidence of GH-PE, but also is associated with a reduction in incidence of various types of PE. Concurrent PA and PP do not show association with a reduction in incidence of GH-PE. PMID:26731265

Cross-Sectional Associations of Depressive Symptom Severity and Functioning with Health Service Use by Older People in Low-and-Middle Income Countries

PubMed Central

Twomey, Conal D.; Prince, Martin; Cieza, Alarcos; Baldwin, David S.; Prina, A. Matthew

2015-01-01

Background: Comprehensive understanding of the determinants of health service use (HSU) by older people with depression is essential for health service planning for an ageing global population. This study aimed to determine the extent to which depressive symptom severity and functioning are associated with HSU by older people with depression in low and middle income countries (LMICs). Methods: A cross-sectional analysis of the 10/66 Dementia Research Group population-based surveys dataset. Participants (n = 4590) were those aged 65 or older, in the clinical range for depressive symptoms (defined as scoring four or more on the EURO-D), living in 13 urban and/or rural catchment areas in nine LMICs. Associations were calculated using Poisson regression and random-effects meta-analysis. Results: After adjustment for confounding variables, (EURO-D) depressive symptom severity was significantly associated with “any community HSU” (Pooled Prevalence Ratios = 1.02; 95% CI = 1.01–1.03) but not hospital admission. Conversely, after adjustment, (WHODAS-II) functioning was significantly associated with hospital admission (Pooled PR = 1.14; 95% CI = 1.02–1.26) but not “any community HSU”. Conclusions: Depressive symptom severity does not explain a large proportion of the variance in HSU by older people with depression in LMICs. The association of functioning with this HSU is worthy of further investigation. In LMICs, variables related to accessibility may be more important correlates of HSU than variables directly related to health problems. PMID:25849540

Estimation of Causal Mediation Effects for a Dichotomous Outcome in Multiple-Mediator Models using the Mediation Formula

PubMed Central

Nelson, Suchitra; Albert, Jeffrey M.

2013-01-01

Mediators are intermediate variables in the causal pathway between an exposure and an outcome. Mediation analysis investigates the extent to which exposure effects occur through these variables, thus revealing causal mechanisms. In this paper, we consider the estimation of the mediation effect when the outcome is binary and multiple mediators of different types exist. We give a precise definition of the total mediation effect as well as decomposed mediation effects through individual or sets of mediators using the potential outcomes framework. We formulate a model of joint distribution (probit-normal) using continuous latent variables for any binary mediators to account for correlations among multiple mediators. A mediation formula approach is proposed to estimate the total mediation effect and decomposed mediation effects based on this parametric model. Estimation of mediation effects through individual or subsets of mediators requires an assumption involving the joint distribution of multiple counterfactuals. We conduct a simulation study that demonstrates low bias of mediation effect estimators for two-mediator models with various combinations of mediator types. The results also show that the power to detect a non-zero total mediation effect increases as the correlation coefficient between two mediators increases, while power for individual mediation effects reaches a maximum when the mediators are uncorrelated. We illustrate our approach by applying it to a retrospective cohort study of dental caries in adolescents with low and high socioeconomic status. Sensitivity analysis is performed to assess the robustness of conclusions regarding mediation effects when the assumption of no unmeasured mediator-outcome confounders is violated. PMID:23650048

Poverty, Pregnancy, and Birth Outcomes: A Study of the Earned Income Tax Credit

PubMed Central

Rehkopf, David H.

2015-01-01

Background Economic interventions are increasingly recognized as a mechanism to address perinatal health outcomes among disadvantaged groups. In the United States, the earned income tax credit (EITC) is the largest poverty alleviation program. Little is known about its effects on perinatal health among recipients and their children. We exploit quasi-random variation in the size of EITC payments over time to examine the effects of income on perinatal health. Methods The study sample includes women surveyed in the 1979 National Longitudinal Survey of Youth (N=2,985) and their children born during 1986–2000 (N=4,683). Outcome variables include utilization of prenatal and postnatal care, use of alcohol and tobacco during pregnancy, term birth, birthweight, and breast-feeding status. We examine the health effects of both household income and EITC payment size using multivariable linear regressions. We employ instrumental variables analysis to estimate the causal effect of income on perinatal health, using EITC payment size as an instrument for household income. Results We find that household income and EITC payment size are associated with improvements in several indicators of perinatal health. Instrumental variables analysis, however, does not reveal a causal association between household income and these health measures. Conclusions Our findings suggest that associations between income and perinatal health may be confounded by unobserved characteristics, but that EITC income improves perinatal health. Future studies should continue to explore the impacts of economic interventions on perinatal health outcomes, and investigate how different forms of income transfers may have different impacts. PMID:26212041

Estimation of causal mediation effects for a dichotomous outcome in multiple-mediator models using the mediation formula.

PubMed

Wang, Wei; Nelson, Suchitra; Albert, Jeffrey M

2013-10-30

Mediators are intermediate variables in the causal pathway between an exposure and an outcome. Mediation analysis investigates the extent to which exposure effects occur through these variables, thus revealing causal mechanisms. In this paper, we consider the estimation of the mediation effect when the outcome is binary and multiple mediators of different types exist. We give a precise definition of the total mediation effect as well as decomposed mediation effects through individual or sets of mediators using the potential outcomes framework. We formulate a model of joint distribution (probit-normal) using continuous latent variables for any binary mediators to account for correlations among multiple mediators. A mediation formula approach is proposed to estimate the total mediation effect and decomposed mediation effects based on this parametric model. Estimation of mediation effects through individual or subsets of mediators requires an assumption involving the joint distribution of multiple counterfactuals. We conduct a simulation study that demonstrates low bias of mediation effect estimators for two-mediator models with various combinations of mediator types. The results also show that the power to detect a nonzero total mediation effect increases as the correlation coefficient between two mediators increases, whereas power for individual mediation effects reaches a maximum when the mediators are uncorrelated. We illustrate our approach by applying it to a retrospective cohort study of dental caries in adolescents with low and high socioeconomic status. Sensitivity analysis is performed to assess the robustness of conclusions regarding mediation effects when the assumption of no unmeasured mediator-outcome confounders is violated. Copyright © 2013 John Wiley & Sons, Ltd.

Educational Level Is Related to Physical Fitness in Patients with Type 2 Diabetes – A Cross-Sectional Study

PubMed Central

Allet, Lara; Giet, Olivier; Barral, Jérôme; Junod, Nicolas; Durrer, Dominique; Amati, Francesca; Sykiotis, Gerasimos P.; Marques-Vidal, Pedro; Puder, Jardena J.

2016-01-01

Introduction Low educational level (EL) and low physical fitness are both predictors of increased morbidity and mortality in patients with type 2 diabetes. It is unknown if EL is related to physical fitness. This would have important implication for the treatment approach of patients of low EL. Materials and Methods In 2011/12, we invited participants of a new nationwide Swiss physical activity program for patients with type 2 diabetes to participate in this study. EL was defined by self-report and categorized as low (mandatory education), middle (professional education) or high (high school/university). Physical fitness was determined using 5 validated measures that assessed aerobic fitness, functional lower limb muscle strength, walking speed, balance and flexibility. Potential confounder variables such as other socio-cultural factors, physical activity level, body composition, diabetes-related parameters and complications/co-morbidities as well as well-being were assessed. Results All invited 185 participants (mean age 59.6 ±9.8 yrs, 76 women) agreed to be included. Of all patients, 23.1% had a low, 32.7% a middle and 44.2% a high EL; 41.8% were professionally active. The study population had a mean BMI of 32.4±5.2 kg/m2 and an HbA1c of 7.3±1.3%. The mean diabetes duration was 8.8±7.4 years. In the baseline assessment, higher EL was associated with increased aerobic fitness, increased functional lower limb muscle strength, and increased walking speed using linear regression analysis (values for low, middle and high EL, respectively: 91.8 ± 27.9, 116.4 ± 49.7 and 134.9 ± 60.4 watts for aerobic fitness (p = 0.002), 15 ± 4.7, 13.9 ± 2.7, 12.6 ± 2.9 seconds for strength (p = 0.001) and 8.8 ± 1.6, 8.3 ± 1.4, 7.8 ± 1.4 seconds for walking speed (p = 0.004)). These associations were independent of potential confounders. Overall, aerobic fitness was 46%, functional limb muscle strength 16%, and walking speed 11% higher in patients of high compared to those of low EL. EL was not related to balance or flexibility. Discussion A main strength of the present study is that it addresses a population of importance and a factor (EL) whose understanding can influence future interventions. A second strength is its relatively large sample size of a high-risk population. Third, unlike studies that have shown an association between self-reported fitness and educational level we assessed physical fitness measures by a quantitative and validated test battery using assessors blinded to other data. Another novelty is the extensive evaluation of the role of many relevant confounder variables. Conclusions In conclusion, we show that in patients with type 2 diabetes EL correlates favorably and independently with important health-related physical fitness measures such as aerobic fitness, walking speed, and lower limb strength. Our findings underline that diabetic patients with low EL should be specifically encouraged to participate in physical activity intervention programs to further reduce social disparities in healthcare. Such programs should be structured and integrate the norms, needs and capacities (financial, time, physical capacities and self-efficacy) of this population, and their effectiveness should be tested in future studies. Trial Registration University of Lausanne clinicaltrials.gov NCT01289587 PMID:27732627

Gender differences in factors associated with suicidal ideation and depressive symptoms among middle-aged workers in Japan.

PubMed

Sugawara, Norio; Yasui-Furukori, Norio; Sasaki, Giro; Tanaka, Osamu; Umeda, Takashi; Takahashi, Ippei; Danjo, Kazuma; Matsuzaka, Masashi; Kaneko, Sunao; Nakaji, Shigeyuki

2013-01-01

The purpose of this study was to assess middle-aged Japanese workers for possible gender differences in the risk factors associated with depressive symptoms and suicidal ideation. 5,878 workers (40-60 yr of age) (3,631 males and 2,247 females) were recruited from randomly selected companies in northern Japan. Demographic and lifestyle factors, suicidal ideation rate, and the data for the Brief Job Stress Questionnaire (BJSQ) and the Center for Epidemiologic Studies for Depression scale (CES-D) were obtained from the self-report questionnaires. After adjusting for possible confounding variables, marital status, absent of stress reduction technique and low job compatibility were significant independent risk factors for suicidal ideation among males. In females, marital status, feeling of insufficient sleep and absence of stress reduction techniques were significant independent risk factors after adjusting for all variables. Under the same adjustments, temporary employment also showed a protective effect against female suicidal ideation. In conclusion, our results suggest that factors related to suicidal ideation differed by gender. Different approaches for each gender might be useful in the development of suicide prevention programs. However, interpretation of work-related effects, such as temporary employment, interpersonal conflict and transportation industry, was hampered by lack of data concerning personal income, working hours and organizational commitment. Additional studies are needed to examine the longitudinal relationships between the risk factors associated with suicidal ideation and depressive symptoms.

Dual diagnosis clients' treatment satisfaction - a systematic review

PubMed Central

2011-01-01

Background The aim of this systematic review is to synthesize existing evidence about treatment satisfaction among clients with substance misuse and mental health co-morbidity (dual diagnoses, DD). Methods We examined satisfaction with treatment received, variations in satisfaction levels by type of treatment intervention and by diagnosis (i.e. DD clients vs. single diagnosis clients), and the influence of factors other than treatment type on satisfaction. Peer-reviewed studies published in English since 1970 were identified by searching electronic databases using pre-defined search strings. Results Across the 27 studies that met inclusion criteria, high average satisfaction scores were found. In most studies, integrated DD treatment yielded greater client satisfaction than standard treatment without explicit DD focus. In standard treatment without DD focus, DD clients tended to be less satisfied than single diagnosis clients. Whilst the evidence base on client and treatment variables related to satisfaction is small, it suggested client demographics and symptom severity to be unrelated to treatment satisfaction. However, satisfaction tended to be linked to other treatment process and outcome variables. Findings are limited in that many studies had very small sample sizes, did not use validated satisfaction instruments and may not have controlled for potential confounders. A framework for further research in this important area is discussed. Conclusions High satisfaction levels with current treatment provision, especially among those in integrated treatment, should enhance therapeutic optimism among practitioners dealing with DD clients. PMID:21501510

The Association Between School Bonding and Smoking Amongst Chilean Adolescents.

PubMed

Gaete, Jorge; Montgomery, Alan; Araya, Ricardo

2015-01-01

The objective of the research was to study the association between school bonding dimensions (school commitment and school attachment) and current adolescent smoking in Chile, controlling for confounding variables using the fifth Chilean School Population National Substance Use Survey, 2003 (CHSS-2003) data set. The CHSS-2003 is a stratified cross-sectional survey that gathers information about personal, familial, peer, and school factors and cigarette use using a self-reported questionnaire. Complete data from 21,956 adolescent students for all the variables of interest were used in the analyses. An exploratory factor analysis (EFA) was performed in order to explore the construct validity of the questionnaire and create the main exposure and potential confounding variables. Multivariable logistic regression analyses were undertaken to study the association between school bonding and smoking. The construct validity of the school attachment and school commitment scales was mainly supported by the EFA. Multivariable analyses showed strong evidence that, after adjusting for factors from different domains, school commitment (student's good grades and school attendance) appears to have a clear inverse association with current smoking (odds ratio [OR]=0.46, 95% confidence interval [CI]: 0.38-0.56). On the other hand, school attachment (their feelings towards their school and their teachers) was not associated with adolescent smoking (OR=1.16, 95% CI: 0.88-1.53). School commitment was strongly associated with current smoking. It is important to further study this variable with the aim of ascertaining whether or not interventions that improve school commitment may prevent or reduce smoking amongst adolescent students.

Associations of Cannabis and Cigarette Use with Depression and Anxiety at Age 18: Findings from the Avon Longitudinal Study of Parents and Children

PubMed Central

Gage, Suzanne H.; Hickman, Matthew; Heron, Jon; Munafò, Marcus R.; Lewis, Glyn; Macleod, John; Zammit, Stanley

2015-01-01

Introduction Substance use is associated with common mental health disorders, but the causal effect of specific substances is uncertain. We investigate whether adolescent cannabis and cigarette use is associated with incident depression and anxiety, while attempting to account for confounding and reverse causation. Methods We used data from ALSPAC, a UK birth cohort study, to investigate associations between cannabis or cigarettes (measured at age 16) and depression or anxiety (measured at age 18), before and after adjustment for pre-birth, childhood and adolescent confounders. Our imputed sample size was 4561 participants. Results Both cannabis (unadjusted OR 1.50, 95% CI 1.26, 1.80) and cigarette use (OR 1.37, 95% CI 1.16, 1.61) increased the odds of developing depression. Adjustment for pre-birth and childhood confounders partly attenuated these relationships though strong evidence of association persisted for cannabis use. There was weak evidence of association for cannabis (fully adjusted OR 1.30, 95% CI 0.98, 1.72) and insufficient evidence for association for cigarette use (fully adjusted OR = 0.97, 95% CI 0.75, 1.24) after mutually adjusting for each other, or for alcohol or other substance use. Neither cannabis nor cigarette use were associated with anxiety after adjustment for pre-birth and childhood confounders. Conclusions Whilst evidence of association between cannabis use and depression persisted after adjusting for pre-term and childhood confounders, our results highlight the difficulties in trying to estimate and interpret independent effects of cannabis and tobacco on psychopathology. Complementary methods are required to robustly examine effects of cannabis and tobacco on psychopathology. PMID:25875443

Does sex have an independent effect on thermoeffector responses during exercise in the heat?

PubMed Central

Gagnon, Daniel; Kenny, Glen P

2012-01-01

Although a number of studies have examined potential differences in temperature regulation between males and females during heat stress, conclusions have remained limited as to whether reported differences are due to confounding physical characteristics or to actual differences in the physiological variables of temperature regulation. Recent observations suggest that sex differences in temperature regulation, particularly in sudomotor activity, go beyond those associated with physical characteristics. Females have recently been shown to have a lower sudomotor activity, as well as a lower thermosensitivity of the response compared to males during exercise performed at a fixed rate of metabolic heat production. Furthermore, sex differences in local and whole-body sudomotor activity are only evident above a certain combination of environmental conditions and rate of metabolic heat production. In contrast, both the onset threshold and thermosensitivity of cutaneous vasodilatation are similar between males and females. In theory, differences in the thermosensitivity of sudomotor activity could be related to either a central (neural activity/integration) and/or peripheral (effector organ) modulation of temperature regulation. Based on recent findings, sex differences in sudomotor activity appear to be mediated peripherally, although a central modulation has yet to be conclusively ruled out. Here we present a brief yet comprehensive review of the current state of knowledge pertaining to sex differences in temperature regulation during exercise in the heat. PMID:23045336

Bilingualism and Cognitive Decline: A Story of Pride and Prejudice.

PubMed

Woumans, Evy; Versijpt, Jan; Sieben, Anne; Santens, Patrick; Duyck, Wouter

2017-01-01

In a recent review, Mukadam, Sommerlad, and Livingston (2017) argue that bilingualism offers no protection against cognitive decline. The authors examined the results of 13 studies (five prospective, eight retrospective) in which monolinguals and bilinguals were compared for cognitive decline and onset of dementia symptoms. Analysis of four of the five prospective studies resulted in the conclusion that there was no difference between monolinguals and bilinguals, whereas seven of the eight retrospective studies actually showed bilingualism to result in a four-to-five year delay of symptom onset. The authors decided to ignore the results from the retrospective studies in favor of those from the prospective studies, reasoning that the former may be confounded by participants' cultural background and education levels. In this commentary, we argue that most of these studies actually controlled for these two variables and still found a positive effect of bilingualism. Furthermore, we argue that the meta-analysis of the prospective studies is not complete, lacking the results of two crucial reports. We conclude that the literature offers substantial evidence for a bilingual effect on the development of cognitive decline and dementia.

Identifying technical aliases in SELDI mass spectra of complex mixtures of proteins

PubMed Central

2013-01-01

Background Biomarker discovery datasets created using mass spectrum protein profiling of complex mixtures of proteins contain many peaks that represent the same protein with different charge states. Correlated variables such as these can confound the statistical analyses of proteomic data. Previously we developed an algorithm that clustered mass spectrum peaks that were biologically or technically correlated. Here we demonstrate an algorithm that clusters correlated technical aliases only. Results In this paper, we propose a preprocessing algorithm that can be used for grouping technical aliases in mass spectrometry protein profiling data. The stringency of the variance allowed for clustering is customizable, thereby affecting the number of peaks that are clustered. Subsequent analysis of the clusters, instead of individual peaks, helps reduce difficulties associated with technically-correlated data, and can aid more efficient biomarker identification. Conclusions This software can be used to pre-process and thereby decrease the complexity of protein profiling proteomics data, thus simplifying the subsequent analysis of biomarkers by decreasing the number of tests. The software is also a practical tool for identifying which features to investigate further by purification, identification and confirmation. PMID:24010718

Statistical aspects of point count sampling

USGS Publications Warehouse

Barker, R.J.; Sauer, J.R.; Ralph, C.J.; Sauer, J.R.; Droege, S.

1995-01-01

The dominant feature of point counts is that they do not census birds, but instead provide incomplete counts of individuals present within a survey plot. Considering a simple model for point count sampling, we demon-strate that use of these incomplete counts can bias estimators and testing procedures, leading to inappropriate conclusions. A large portion of the variability in point counts is caused by the incomplete counting, and this within-count variation can be confounded with ecologically meaningful varia-tion. We recommend caution in the analysis of estimates obtained from point counts. Using; our model, we also consider optimal allocation of sampling effort. The critical step in the optimization process is in determining the goals of the study and methods that will be used to meet these goals. By explicitly defining the constraints on sampling and by estimating the relationship between precision and bias of estimators and time spent counting, we can predict the optimal time at a point for each of several monitoring goals. In general, time spent at a point will differ depending on the goals of the study.

Age-related decline in cognitive control: the role of fluid intelligence and processing speed

PubMed Central

2014-01-01

Background Research on cognitive control suggests an age-related decline in proactive control abilities whereas reactive control seems to remain intact. However, the reason of the differential age effect on cognitive control efficiency is still unclear. This study investigated the potential influence of fluid intelligence and processing speed on the selective age-related decline in proactive control. Eighty young and 80 healthy older adults were included in this study. The participants were submitted to a working memory recognition paradigm, assessing proactive and reactive cognitive control by manipulating the interference level across items. Results Repeated measures ANOVAs and hierarchical linear regressions indicated that the ability to appropriately use cognitive control processes during aging seems to be at least partially affected by the amount of available cognitive resources (assessed by fluid intelligence and processing speed abilities). Conclusions This study highlights the potential role of cognitive resources on the selective age-related decline in proactive control, suggesting the importance of a more exhaustive approach considering the confounding variables during cognitive control assessment. PMID:24401034

Determinants of passive smoking in children in Edinburgh, Scotland.

PubMed Central

Jarvis, M J; Strachan, D P; Feyerabend, C

1992-01-01

OBJECTIVES. Using saliva cotinine as a quantitative marker, we examined the contribution of factors other than parental smoking to children's passive exposure to tobacco smoke. METHODS. Saliva specimens from a random sample of 734 7-year-old schoolchildren in Edinburgh, Scotland, were analyzed for cotinine. Their parents completed a questionnaire covering smoking habits and conditions in the home. RESULTS. A number of independent predictors of cotinine were identified in addition to the main one of smoking by household members. These predictors included home ownership, social class, day of the week, season of the year, number of parents present, crowding in the home, the number of children in the household, and sex. Cotinine was higher in children from less advantaged backgrounds, during winter, on Mondays, in girls, and when fewer other children were present. The effects were similar between children from nonsmoking and smoking homes. CONCLUSIONS. Questionnaire measures of parental smoking are insufficient to fully characterize young children's exposure to passive smoking. Because socioeconomic variables contribute to measured exposure, passive-smoking studies that treat class as a confounder and control for it may be overcontrolling. PMID:1503162

[Post-academic dental specialties. 11. Discomfort during atraumatic restorative treatment (ART) versus conventional restorative treatment].

PubMed

van Gemert-Schriks, M C M

2007-05-01

Although Atraumatic Restorative Treatment (ART) claims to be a patient-friendly method of treatment, little scientific proof of this is available. The aim of this study, therefore, was to acquire a reliable measurement of the degree of discomfort which children experience during dental treatment performed according to the ART approach and during the conventional method. A number of 403 Indonesian schoolchildren were randomly divided into 2 groups. In each child, one class II restoration was carried out on a deciduous molar either by means of ART or the use of rotary instruments (750 rpm). Discomfort scores were determined both by physiological measurements (heart rate) and behavioral observations (Venham scale). Venham scores showed a marked difference between the 2 groups, whereas heart rate scores only differed significantly during deep excavation. A correlation was found between Venham scores and heart rate measurements. Sex, initial anxiety and performing dentist were shown to be confounding variables. In conclusion it can be said that children treated according to the ART approach experience less discomfort than those treated with rotary instruments.

A biological evaluation of DNA damage detected by comet assay in healthy populations residing in areas that differ in lung cancer incidence.

PubMed

Heepchantree, Worapa; Paratasilpin, Thipmani; Kangwanpong, Daoroong

2006-06-01

The comet assay was performed to evaluate the effect of environmental exposure between human populations residing in two areas that differ in lung cancer incidence, Saraphi (n = 91) and Chom Thong (n = 94). Three parameters, the tail length, tail intensity, and tail moment, were used to detect DNA damage in peripheral blood and stimulated lymphocytes with and without the DNA repair inhibitor, aphidicolin. Internal standards, cryopreserved isolated lymphocytes, and isolated lymphocytes irradiated with 2 Gy gamma rays, were used to correct the interexperimental variability. Results revealed a significant difference between two populations only when the tail length was used to measure DNA damage. The evaluation of various potential confounding factors, such as gender, pesticide exposure, smoking, alcohol drinking, and fermented tea leaf or betel nut chewing, indicated no significant influence in DNA damage. In conclusion, significant difference in DNA damage, detected only by tail length between the two populations residing in the areas with different incidence of lung cancer, may reflect a nonhazardous level of exposure to toxic substances.

[Association between physical fitness parameters and health related quality of life in Chilean community-dwelling older adults].

PubMed

Guede Rojas, Francisco; Chirosa Ríos, Luis Javier; Fuentealba Urra, Sergio; Vergara Ríos, César; Ulloa Díaz, David; Campos Jara, Christian; Barbosa González, Paola; Cuevas Aburto, Jesualdo

2017-01-01

There is no conclusive evidence about the association between physical fitness (PF) and health related quality of life (HRQOL) in older adults. To seek for an association between PF and HRQOL in non-disabled community-dwelling Chilean older adults. One hundred and sixteen subjects participated in the study. PF was assessed using the Senior Fitness Test (SFT) and hand grip strength (HGS). HRQOL was assessed using eight dimensions provided by the SF-12v2 questionnaire. Binary multivariate logistic regression models were carried out considering the potential influence of confounder variables. Non-adjusted models, indicated that subjects with better performance in arm curl test (ACT) were more likely to score higher on vitality dimension (OR > 1) and those with higher HGS were more likely to score higher on physical functioning, bodily pain, vitality and mental health (OR > 1). The adjusted models consistently showed that ACT and HGS predicted a favorable perception of vitality and mental health dimensions respectively (OR > 1). HGS and ACT have a predictive value for certain dimensions of HRQOL.

Developing a spatial-statistical model and map of historical malaria prevalence in Botswana using a staged variable selection procedure

PubMed Central

Craig, Marlies H; Sharp, Brian L; Mabaso, Musawenkosi LH; Kleinschmidt, Immo

2007-01-01

Background Several malaria risk maps have been developed in recent years, many from the prevalence of infection data collated by the MARA (Mapping Malaria Risk in Africa) project, and using various environmental data sets as predictors. Variable selection is a major obstacle due to analytical problems caused by over-fitting, confounding and non-independence in the data. Testing and comparing every combination of explanatory variables in a Bayesian spatial framework remains unfeasible for most researchers. The aim of this study was to develop a malaria risk map using a systematic and practicable variable selection process for spatial analysis and mapping of historical malaria risk in Botswana. Results Of 50 potential explanatory variables from eight environmental data themes, 42 were significantly associated with malaria prevalence in univariate logistic regression and were ranked by the Akaike Information Criterion. Those correlated with higher-ranking relatives of the same environmental theme, were temporarily excluded. The remaining 14 candidates were ranked by selection frequency after running automated step-wise selection procedures on 1000 bootstrap samples drawn from the data. A non-spatial multiple-variable model was developed through step-wise inclusion in order of selection frequency. Previously excluded variables were then re-evaluated for inclusion, using further step-wise bootstrap procedures, resulting in the exclusion of another variable. Finally a Bayesian geo-statistical model using Markov Chain Monte Carlo simulation was fitted to the data, resulting in a final model of three predictor variables, namely summer rainfall, mean annual temperature and altitude. Each was independently and significantly associated with malaria prevalence after allowing for spatial correlation. This model was used to predict malaria prevalence at unobserved locations, producing a smooth risk map for the whole country. Conclusion We have produced a highly plausible and parsimonious model of historical malaria risk for Botswana from point-referenced data from a 1961/2 prevalence survey of malaria infection in 1–14 year old children. After starting with a list of 50 potential variables we ended with three highly plausible predictors, by applying a systematic and repeatable staged variable selection procedure that included a spatial analysis, which has application for other environmentally determined infectious diseases. All this was accomplished using general-purpose statistical software. PMID:17892584

Patient-independent variables affecting the assessment of aspirin responsiveness by serum thromboxane measurement.

PubMed

Petrucci, Giovanna; Rizzi, Alessandro; Cavalca, Viviana; Habib, Aida; Pitocco, Dario; Veglia, Fabrizio; Ranalli, Paola; Zaccardi, Francesco; Pagliaccia, Francesca; Tremoli, Elena; Patrono, Carlo; Rocca, Bianca

2016-10-28

The serum TXB 2 (sTXB 2 ) assay reflects the pharmacodynamics of platelet inhibition by low-dose aspirin. However, different studies reported variable sTXB 2 values. sTXB 2 assay requires whole blood incubation at 37 °C as a condition for optimal thrombin generation, arachidonic acid release and its metabolism by platelet cyclooxygenase-1 to form TXA 2 . Access to 37 °C incubation may be variably delayed, and different methods to quantitate sTXB 2 may contribute to variable results between different Centers. We investigated whether delaying 37 °C incubation and/or analytical issues affect sTXB 2 concentrations, biasing the assessment of aspirin responsiveness. Sixty-eight samples from 54 volunteers, on- and off-aspirin, were incubated at 37 °C immediately after sampling (reference sample) or after 5, 10, 15, 20, 30 or 60 minutes at room temperature (RT); 8 samples remained at RT 60 minutes, without subsequent incubation; 314 sera were measured by enzyme immunoassay (EIA) and liquid chromatography-tandem mass-spectrometry (LC/MS-MS) methods. sTXB 2 concentrations decreased exponentially as a function of the delay before 37 °C incubation, ranging from 94 ± 11 % at 5 minutes to 23 ± 22 % of the reference sample after 60 minutes at RT. There was high agreement between EIA and LC/MS-MS. Moreover, we simulated the influence of a 15- or 30-minute delayed incubation on 300 sTXB2 measurements from previously-studied, aspirin-treated patients. Delayed incubation reduced the percentage of aspirin 'non-responders' by 22 % to 52 %, depending on the response threshold. In conclusion, a variable delay in the 37 °C incubation of blood samples may affect the assessment of platelet cyclooxygenase-1 inhibition by aspirin and confound the characterization of the determinants of aspirin responsiveness.

Physical health-related quality of life in relation to metabolic health and obesity among men and women in Germany.

PubMed

Truthmann, Julia; Mensink, Gert B M; Bosy-Westphal, Anja; Hapke, Ulfert; Scheidt-Nave, Christa; Schienkiewitz, Anja

2017-06-10

This study examined sex-specific differences in physical health-related quality of life (HRQoL) across subgroups of metabolic health and obesity. We specifically asked whether (1) obesity is related to lower HRQoL independent of metabolic health status and potential confounders, and (2) whether associations are similar in men and women. We used cross-sectional data from the German Health Interview and Examination Survey 2008-11. Physical HRQoL was measured using the Short Form-36 version 2 physical component summary (PCS) score. Based on harmonized ATPIII criteria for the definition of the metabolic health and a body mass index ≥ 30 kg/m 2 to define obesity, individuals were classified as metabolically healthy non-obese (MHNO), metabolically unhealthy non-obese (MUNO), metabolically healthy obese (MHO), and metabolically unhealthy obese (MUO). Sex-specific analyses including multivariable linear regression analyses were based on PCS as the dependent variable, metabolic health and obesity category as the independent variable with three categories and MHNO as the reference, and age, education, lifestyle and comorbidities as confounders. This study included 6860 participants (3298 men, 3562 women). Compared to MHNO, all other metabolic health and obesity categories had significantly lower PCS in both sexes. As reflected by the beta coefficients [95% confidence interval] from bivariable linear regression models, a significant inverse association with PCS was strongest for MUO (men: -7.0 [-8.2; -5.8]; women: -9.0 [-10.2; -7.9]), intermediate for MUNO (men: -4.2 [-5.3; -3.1]; women: -5.6 [-6.8; -4.4]) and least pronounced for MHO (men: -2.2 [-3.6; -0.8]; women -3.9 [-5.4; -2.5]). Differences in relation to MHNO remained statistically significant for all groups after adjusting for confounders, but decreased in particular for MUNO (men:-1.3 [-2.3; -0.3]; women: -1.5 [-2.7; -0.3]. Obesity was significantly related to lower physical HRQoL, independent of metabolic health status. Potential confounders including age, educational status, health-related behaviors, and comorbidities explained parts of the inverse relationship. Associations were evident in both sexes and consistently more pronounced among women than men.

Simpson's Paradox and Confounding Factors in University Rankings: A Demonstration Using QS 2011-12 Data

ERIC Educational Resources Information Center

Soh, Kay Cheng

2012-01-01

University ranking has become ritualistic in higher education. Ranking results are taken as bona fide by rank users. Ranking systems usually use large data sets from highly heterogeneous universities of varied backgrounds. This poses the problem of Simpson's Paradox and the lurking variables causing it. Using QS 2011-2012 Ranking data, the dual…

Maternal Pre-Pregnancy Body Mass Index and Offspring Temperament and Behavior at 1 and 2 Years of Age

ERIC Educational Resources Information Center

Van Lieshout, Ryan J.; Schmidt, Louis A.; Robinson, Monique; Niccols, Alison; Boyle, Michael H.

2013-01-01

Recent research suggests that fetal exposure to increased maternal body mass index (BMI) during pregnancy may be associated with psychopathology later in life. When this link first emerges, and if it is due to intrauterine exposures or confounding variables is not known. We therefore assessed associations between maternal pre-pregnancy BMI and:…

The Effects of Age on Second Language Grammar and Speech Production

ERIC Educational Resources Information Center

Huang, Becky H.

2014-01-01

The current study examined the age of learning effect on second language (L2) acquisition. The research goals of the study were twofold: to test whether there is an independent age effect controlling for other potentially confounding variables, and to clarify the age effect across L2 grammar and speech production domains. The study included 118…

Reduced streamflow lowers dry-season growth of rainbow trout in a small stream

Treesearch

Bret C. Harvey; Rodney J. Nakamoto; Jason L. White

2006-01-01

A wide variety of resource management activities can affect surface discharge in small streams. Often, the effects of variation in streamflow on fish survival and growth can be difficult to estimate because of possible confounding with the effects of other variables, such as water temperature and fish density. We measured the effect of streamflow on survival and growth...

Individual tree differences confound effects of growth regulators in rooting sugar maple softwood cuttings

Treesearch

John R. Donnelly

1971-01-01

Softwood stem cuttings from three mature sugar maple trees were treated with several types and concentrations of growth regulators. Lack of statistical significance was due to extreme variability in tree response: low levels of auxin stimulated rooting in two study trees, while auxins inhibited rooting in the other tree. It is postulated that variations in rooting...

The Chabot Emotional Differentiation Scale: A Theoretically and Psychometrically Sound Instrument for Measuring Bowen's Intrapsychic Aspect of Differentiation

ERIC Educational Resources Information Center

Licht, Carolyn; Chabot, David

2006-01-01

Bowen's theory (1978) of differentiation is the personality variable most critical to mature development and the attainment of psychological health. The study of psychological differentiation has been confounded by confusion regarding the constructs being studied and the measurement tools used to assess them. The purpose of this review is to…

Measuring the wetting angle and perimeter of single wood pulp fibers : a modified method

Treesearch

John H. Klungness

1981-01-01

In pulp processing development it is often necessary to measure the effect of a process variable on individual pulp fiber wettability. Such processes would include drying of market pulps, recycling of secondary fibers, and surface modification of fibers as in sizing. However, if wettability is measured on a fiber sheet surface, the results are confounded by...

Do Fraternities and Sororities Still Enhance Socially Responsible Leadership? Evidence from the Fourth Year of College

ERIC Educational Resources Information Center

Hevel, Michael S.; Martin, Georgianna L.; Pascarella, Ernest T.

2014-01-01

We use a longitudinal national dataset to explore the effects of fraternity and sorority membership on students' socially responsible leadership in the fourth year of college. Controlling for a variety of potentially confounding variables, we find no net effect. These findings run counter to an earlier study based on the same students that found…

Uncovering noisy social signals: Using optimization methods from experimental physics to study social phenomena.

PubMed

Kaptein, Maurits; van Emden, Robin; Iannuzzi, Davide

2017-01-01

Due to the ubiquitous presence of treatment heterogeneity, measurement error, and contextual confounders, numerous social phenomena are hard to study. Precise control of treatment variables and possible confounders is often key to the success of studies in the social sciences, yet often proves out of the realm of control of the experimenter. To amend this situation we propose a novel approach coined "lock-in feedback" which is based on a method that is routinely used in high-precision physics experiments to extract small signals out of a noisy environment. Here, we adapt the method to noisy social signals in multiple dimensions and evaluate it by studying an inherently noisy topic: the perception of (subjective) beauty. We show that the lock-in feedback approach allows one to select optimal treatment levels despite the presence of considerable noise. Furthermore, through the introduction of an external contextual shock we demonstrate that we can find relationships between noisy variables that were hitherto unknown. We therefore argue that lock-in methods may provide a valuable addition to the social scientist's experimental toolbox and we explicitly discuss a number of future applications.

Social class, income, education, area of residence and psychological distress: does social class have an independent effect on psychological distress in Antalya, Turkey?

PubMed

Belek, I

2000-02-01

The aim of this study is to determine the separate effects of social class, income, education and area of residence on psychological distress. The study also assesses whether the association between prevalence of high score on the 12-item General Health Questionnaire (GHQ 12) and social class is independent of other variables. Psychological distress was assessed by means of the GHQ 12. The study covered 1,092 adults aged 15 years or more living in two different quarters of Antalya. Social class status was defined by occupational position, with income, education and area of residence treated as confounders. Chi-square and logistic regression analyses were used to evaluate the data. Large inequalities in psychological distress by all variables were observed. Psychological distress was significantly associated with class status, after adjusting for income, education, area of residence and other potential confounders (age, sex and marital status). Class inequalities in psychological distress were observed between blue-collar workers/unqualified employees and bourgeoisie. These findings support the view that the recent widening of inequalities among social classes in Turkey pose a substantial threat to health.

The influence of depression on personality traits in patients with fibromyalgia: a case-control study.

PubMed

Santos, Daniela M; Lage, Laís V; Jabur, Eleonora K; Kaziyama, Helena H S; Iosifescu, Dan V; De Lucia, Mara Cristina S; Fráguas, Renério

2017-01-01

We developed this study to investigate the association of fibromyalgia with personality traits, controlling for depression and other potential confounders. We assessed personality traits using the Cloninger's Temperament and Character Inventory (TCI) in 78 female patients with fibromyalgia and in a control group of 78 subjects without fibromyalgia. The Mini-International Neuropsychiatric Interview was used to assess depression and anxiety diagnoses. To investigate the association between fibromyalgia and the Cloninger's Temperament and Character Inventory we performed unadjusted and adjusted analyses of covariance, using the TCI score as dependent variable and adjusting the model for depression, anxiety and for clinical and socio-demographic variables. We used a backward selection method to choose the final model. In the unadjusted analysis, fibromyalgia was associated with all personality traits, except persistency. After adjusting for depression and anxiety, patients with fibromyalgia presented decreased novelty seeking compared to controls; the differences in other personality traits were no longer significant. Novelty seeking was also correlated with the length of history of fibromyalgia and pain intensity. Decreased novelty seeking may be a personality trait associated with fibromyalgia. Depression and anxiety should be considered potential confounders in the evaluation of personality traits in this population.

Uncovering noisy social signals: Using optimization methods from experimental physics to study social phenomena

PubMed Central

2017-01-01

Due to the ubiquitous presence of treatment heterogeneity, measurement error, and contextual confounders, numerous social phenomena are hard to study. Precise control of treatment variables and possible confounders is often key to the success of studies in the social sciences, yet often proves out of the realm of control of the experimenter. To amend this situation we propose a novel approach coined “lock-in feedback” which is based on a method that is routinely used in high-precision physics experiments to extract small signals out of a noisy environment. Here, we adapt the method to noisy social signals in multiple dimensions and evaluate it by studying an inherently noisy topic: the perception of (subjective) beauty. We show that the lock-in feedback approach allows one to select optimal treatment levels despite the presence of considerable noise. Furthermore, through the introduction of an external contextual shock we demonstrate that we can find relationships between noisy variables that were hitherto unknown. We therefore argue that lock-in methods may provide a valuable addition to the social scientist’s experimental toolbox and we explicitly discuss a number of future applications. PMID:28306728

Genetic Instrumental Variable Studies of Effects of Prenatal Risk Factors

PubMed Central

von Hinke Kessler Scholder, Stephanie

2013-01-01

Identifying the effects of maternal risk factors during pregnancy on infant and child health is an area of tremendous research interest. However, of interest to policy makers is unraveling the causal effects of prenatal risk factors, not their associations with child health, which may be confounded by several unobserved factors. In this paper, we evaluate the utility of genetic variants in three genes that have unequivocal evidence of being related to three major risk factors – CHRNA3 for smoking, ADH1B for alcohol use, and FTO for obesity – as instrumental variables for identifying the causal effects of such factors during pregnancy. Using two independent datasets, we find that these variants are overall predictive of the risk factors and are not systematically related to observed confounders, suggesting that they may be useful instruments. We also find some suggestive evidence that genetic effects are stronger during than before pregnancy. We provide an empirical example illustrating the use of these genetic variants as instruments to evaluate the effects of risk factors on birth weight. Finally, we offer suggestions for researchers contemplating the use of these variants as instruments. PMID:23701534

Confounder summary scores when comparing the effects of multiple drug exposures.

PubMed

Cadarette, Suzanne M; Gagne, Joshua J; Solomon, Daniel H; Katz, Jeffrey N; Stürmer, Til

2010-01-01

Little information is available comparing methods to adjust for confounding when considering multiple drug exposures. We compared three analytic strategies to control for confounding based on measured variables: conventional multivariable, exposure propensity score (EPS), and disease risk score (DRS). Each method was applied to a dataset (2000-2006) recently used to examine the comparative effectiveness of four drugs. The relative effectiveness of risedronate, nasal calcitonin, and raloxifene in preventing non-vertebral fracture, were each compared to alendronate. EPSs were derived both by using multinomial logistic regression (single model EPS) and by three separate logistic regression models (separate model EPS). DRSs were derived and event rates compared using Cox proportional hazard models. DRSs derived among the entire cohort (full cohort DRS) was compared to DRSs derived only among the referent alendronate (unexposed cohort DRS). Less than 8% deviation from the base estimate (conventional multivariable) was observed applying single model EPS, separate model EPS or full cohort DRS. Applying the unexposed cohort DRS when background risk for fracture differed between comparison drug exposure cohorts resulted in -7 to + 13% deviation from our base estimate. With sufficient numbers of exposed and outcomes, either conventional multivariable, EPS or full cohort DRS may be used to adjust for confounding to compare the effects of multiple drug exposures. However, our data also suggest that unexposed cohort DRS may be problematic when background risks differ between referent and exposed groups. Further empirical and simulation studies will help to clarify the generalizability of our findings.

Studying neuroanatomy using MRI.

PubMed

Lerch, Jason P; van der Kouwe, André J W; Raznahan, Armin; Paus, Tomáš; Johansen-Berg, Heidi; Miller, Karla L; Smith, Stephen M; Fischl, Bruce; Sotiropoulos, Stamatios N

2017-02-23

The study of neuroanatomy using imaging enables key insights into how our brains function, are shaped by genes and environment, and change with development, aging and disease. Developments in MRI acquisition, image processing and data modeling have been key to these advances. However, MRI provides an indirect measurement of the biological signals we aim to investigate. Thus, artifacts and key questions of correct interpretation can confound the readouts provided by anatomical MRI. In this review we provide an overview of the methods for measuring macro- and mesoscopic structure and for inferring microstructural properties; we also describe key artifacts and confounds that can lead to incorrect conclusions. Ultimately, we believe that, although methods need to improve and caution is required in interpretation, structural MRI continues to have great promise in furthering our understanding of how the brain works.

Reporting of methodological features in observational studies of pre-harvest food safety.

PubMed

Sargeant, Jan M; O'Connor, Annette M; Renter, David G; Kelton, David F; Snedeker, Kate; Wisener, Lee V; Leonard, Erin K; Guthrie, Alessia D; Faires, Meredith

2011-02-01

Observational studies in pre-harvest food safety may be useful for identifying risk factors and for evaluating potential mitigation strategies to reduce foodborne pathogens. However, there are no structured reporting guidelines for these types of study designs in livestock species. Our objective was to evaluate the reporting of observational studies in the pre-harvest food safety literature using guidelines modified from the human healthcare literature. We identified 100 pre-harvest food safety studies published between 1999 and 2009. Each study was evaluated independently by two reviewers using a structured checklist. Of the 38 studies that explicitly stated the observational study design, 27 were described as cross-sectional studies, eight as case-control studies, and three as cohort studies. Study features reported in over 75% of the selected studies included: description of the geographic location of the studies, definitions and sources of data for outcomes, organizational level and source of data for independent variables, description of statistical methods and results, number of herds enrolled in the study and included in the analysis, and sources of study funding. However, other features were not consistently reported, including details related to eligibility criteria for groups (such as barn, room, or pen) and individuals, numbers of groups and individuals included in various stages of the study, identification of primary outcomes, the distinction between putative risk factors and confounding variables, the identification of a primary exposure variable, the referent level for evaluation of categorical variable associations, methods of controlling confounding variables and missing variables, model fit, details of subset analysis, demographic information at the sampling unit level, and generalizability of the study results. Improvement in reporting of observational studies of pre-harvest food safety will aid research readers and reviewers in interpreting and evaluating the results of such studies. Copyright © 2010 Elsevier B.V. All rights reserved.

ABCB1 haplotype and OPRM1 118A > G genotype interaction in methadone maintenance treatment pharmacogenetics

PubMed Central

Barratt, Daniel T; Coller, Janet K; Hallinan, Richard; Byrne, Andrew; White, Jason M; Foster, David JR; Somogyi, Andrew A

2012-01-01

Background: Genetic variability in ABCB1, encoding the P-glycoprotein efflux transporter, has been linked to altered methadone maintenance treatment dose requirements. However, subsequent studies have indicated that additional environmental or genetic factors may confound ABCB1 pharmacogenetics in different methadone maintenance treatment settings. There is evidence that genetic variability in OPRM1, encoding the mu opioid receptor, and ABCB1 may interact to affect morphine response in opposite ways. This study aimed to examine whether a similar gene-gene interaction occurs for methadone in methadone maintenance treatment. Methods: Opioid-dependent subjects (n = 119) maintained on methadone (15–300 mg/day) were genotyped for five single nucleotide polymorphisms of ABCB1 (61A > G; 1199G > A; 1236C > T; 2677G > T; 3435C > T), as well as for the OPRM1 118A > G single nucleotide polymorphism. Subjects’ methadone doses and trough plasma (R)-methadone concentrations (Ctrough) were compared between ABCB1 haplotypes (with and without controlling for OPRM1 genotype), and between OPRM1 genotypes (with and without controlling for ABCB1 haplotype). Results: Among wild-type OPRM1 subjects, an ABCB1 variant haplotype group (subjects with a wild-type and 61A:1199G:1236C:2677T:3435T haplotype combination, or homozygous for the 61A:1199G:1236C:2677T:3435T haplotype) had significantly lower doses (median ± standard deviation 35 ± 5 versus 180 ± 65 mg/day, P < 0.01) and Ctrough (78 ± 22 versus 177 ± 97 ng/mL, P < 0.05) than ABCB1 wild-type subjects. Among subjects with the most common ABCB1 haplotype combination (wild-type with 61A:1199G:1236T:2677T:3435T), the OPRM1 118 A/G genotype was associated with a significantly higher Ctrough than 118 A/A (250 ± 126 versus 108 ± 36 ng/mL, P = 0.016). No ABCB1 haplotype group or OPRM1 genotype was associated with dose or Ctrough without taking into account confounding genetic variability at the other locus. Therefore, two interacting pharmacogenetic determinants of methadone maintenance treatment response were identified, ie, ABCB1, where variants are associated with lower methadone requirements, and OPRM1, where the variant is associated with higher methadone requirements. Conclusion: These opposing pharmacogenetic effects therefore need to be considered in combination when assessing methadone maintenance treatment pharmacogenetics. PMID:23226062

Effects of context and word class on lexical retrieval in Chinese speakers with anomic aphasia

PubMed Central

Law, Sam-Po; Kong, Anthony Pak-Hin; Lai, Loretta Wing-Shan; Lai, Christy

2014-01-01

Background Differences in processing nouns and verbs have been investigated intensely in psycholinguistics and neuropsychology in past decades. However, the majority of studies examining retrieval of these word classes have involved tasks of single word stimuli or responses. While the results have provided rich information for addressing issues about grammatical class distinctions, it is unclear whether they have adequate ecological validity for understanding lexical retrieval in connected speech which characterizes daily verbal communication. Previous investigations comparing retrieval of nouns and verbs in single word production and connected speech have reported either discrepant performance between the two contexts with presence of word class dissociation in picture naming but absence in connected speech, or null effects of word class. In addition, word finding difficulties have been found to be less severe in connected speech than picture naming. However, these studies have failed to match target stimuli of the two word classes and between tasks on psycholinguistic variables known to affect performance in response latency and/or accuracy. Aims The present study compared lexical retrieval of nouns and verbs in picture naming and connected speech from picture description, procedural description, and story-telling among 19 Chinese speakers with anomic aphasia and their age, gender, and education matched healthy controls, to understand the influence of grammatical class on word production across speech contexts when target items were balanced for confounding variables between word classes and tasks. Methods & Procedures Elicitation of responses followed the protocol of the AphasiaBank consortium (http://talkbank.org/AphasiaBank/). Target words for confrontation naming were based on well-established naming tests, while those for narrative were drawn from a large database of normal speakers. Selected nouns and verbs in the two contexts were matched for age-of-acquisition (AoA) and familiarity. Influence of imageability was removed through statistical control. Outcomes & Results When AoA and familiarity were balanced, nouns were retrieved better than verbs, and performance was higher in picture naming than connected speech. When imageability was further controlled for, only the effect of task remained significant. Conclusions The absence of word class effects when confounding variables are controlled for is similar to many previous reports; however, the pattern of better word retrieval in naming is rare but compatible with the account that processing demands are higher in narrative than naming. The overall findings have strongly suggested the importance of including connected speech tasks in any language assessment and evaluation of language rehabilitation of individuals with aphasia. PMID:25505810

Investigating the relationship between neighborhood poverty and mortality risk: A marginal structural modeling approach

PubMed Central

Do, D. Phuong; Wang, Lu; Elliott, Michael R.

2013-01-01

Extant observational studies generally support the existence of a link between neighborhood context and health. However, estimating the causal impact of neighborhood effects from observational data has proven to be a challenge. Omission of relevant factors may lead to overestimating the effects of neighborhoods on health while inclusion of time-varying confounders that may also be mediators (e.g., income, labor force status) may lead to underestimation. Using longitudinal data from the 1990 to 2007 years of the Panel Study of Income Dynamics, this study investigates the link between neighborhood poverty and overall mortality risk. A marginal structural modeling strategy is employed to appropriately adjust for simultaneous mediating and confounding factors. To address the issue of possible upward bias from the omission of key variables, sensitivity analysis to assess the robustness of results against unobserved confounding is conducted. We examine two continuous measures of neighborhood poverty – single-point and a running average. Both were specified as piece-wise linear splines with a knot at 20 percent. We found no evidence from the traditional naïve strategy that neighborhood context influences mortality risk. In contrast, for both the single-point and running average neighborhood poverty specifications, the marginal structural model estimates indicated a statistically significant increase in mortality risk with increasing neighborhood poverty above the 20 percent threshold. For example, below 20 percent neighborhood poverty, no association was found. However, after the 20 percent poverty threshold is reached, each 10 percentage point increase in running average neighborhood poverty was found to increase the odds for mortality by 89 percent [95% CI = 1.22, 2.91]. Sensitivity analysis indicated that estimates were moderately robust to omitted variable bias. PMID:23849239

A community study on emotional distress among Arab and Jewish Israelis over the age of 60.

PubMed

Shemesh, Annarosa Anat; Kohn, Robert; Blumstein, Tzvia; Geraisy, Nabil; Novikov, Ilya; Levav, Itzhak

2006-01-01

The elderly constitute a vulnerable group for psychopathology, yet research on their mental health among both Arab and Jews in Israel remains limited. The same is the case in Arab countries. This paper reports on the contrasting distribution of the mean emotional distress (ED) scores and rates of suspected clinical cases, and their related risk factors, among community residents over the age of 60. Several national agencies conducted a survey on 5,055 elderly individuals to investigate their health status, including ED. The interview included socio-demographic and behavioral health items, as well as a modified 12 item-GHQ as a measure of ED. Total ED scores and prevalence rates for suspected psychopathology were calculated. Their respective risk factors were examined using univariate and multivariate methods. The ED scores were highest among Muslim Arabs (4.9), followed by Christian Arabs (4.2), Jews (3.1) and Druzes (2.8). Their estimated prevalence rates were 43.4%, 37.0%, 21.4%, and 17.0%, respectively. The gradient of these results remained unchanged in the multivariate analysis for ED scores adjusting for confounding variables. In contrast, logistic regression analysis controlling for confounding variables did not find a differential risk for suspected psychopathology between Arabs and Jews. Conceivably, the higher demoralization scores among elderly Arabs are associated with their minority status affiliation, as well as with the rapid social changes that have taken place in their midst. A cultural response style may be entertained as a possible explanation. However, these factors do not impact the risk for suspected psychopathology where no differential risk was noted after adjustments for confounders. Copyright 2005 John Wiley & Sons, Ltd.

Accounting for Time-Varying Confounding in the Relationship Between Obesity and Coronary Heart Disease: Analysis With G-Estimation: The ARIC Study.

PubMed

Shakiba, Maryam; Mansournia, Mohammad Ali; Salari, Arsalan; Soori, Hamid; Mansournia, Nasrin; Kaufman, Jay S

2018-06-01

In longitudinal studies, standard analysis may yield biased estimates of exposure effect in the presence of time-varying confounders that are also intermediate variables. We aimed to quantify the relationship between obesity and coronary heart disease (CHD) by appropriately adjusting for time-varying confounders. This study was performed in a subset of participants from the Atherosclerosis Risk in Communities (ARIC) Study (1987-2010), a US study designed to investigate risk factors for atherosclerosis. General obesity was defined as body mass index (weight (kg)/height (m)2) ≥30, and abdominal obesity (AOB) was defined according to either waist circumference (≥102 cm in men and ≥88 cm in women) or waist:hip ratio (≥0.9 in men and ≥0.85 in women). The association of obesity with CHD was estimated by G-estimation and compared with results from accelerated failure-time models using 3 specifications. The first model, which adjusted for baseline covariates, excluding metabolic mediators of obesity, showed increased risk of CHD for all obesity measures. Further adjustment for metabolic mediators in the second model and time-varying variables in the third model produced negligible changes in the hazard ratios. The hazard ratios estimated by G-estimation were 1.15 (95% confidence interval (CI): 0.83, 1.47) for general obesity, 1.65 (95% CI: 1.35, 1.92) for AOB based on waist circumference, and 1.38 (95% CI: 1.13, 1.99) for AOB based on waist:hip ratio, suggesting that AOB increased the risk of CHD. The G-estimated hazard ratios for both measures were further from the null than those derived from standard models.

The role of job strain in understanding midlife common mental disorder: a national birth cohort study.

PubMed

Harvey, Samuel B; Sellahewa, Dilan A; Wang, Min-Jung; Milligan-Saville, Josie; Bryan, Bridget T; Henderson, Max; Hatch, Stephani L; Mykletun, Arnstein

2018-06-01

Long-standing concerns exist about reverse causation and residual confounding in the prospective association between job strain and risk of future common mental disorders. We aimed to address these concerns through analysis of data collected in the UK National Child Development Study, a large British cohort study. Data from the National Child Development Study (n=6870) were analysed by use of multivariate logistic regression to investigate the prospective association between job strain variables at age 45 years and risk of future common mental disorders at age 50 years, controlling for lifetime psychiatric history and a range of other possible confounding variables across the lifecourse. Population attributable fractions were calculated to estimate the public health effect of job strain on midlife mental health. In the final model, adjusted for all measured confounders, high job demands (odds ratio 1·70, 95% CI 1·25-2·32; p=0·0008), low job control (1·89, 1·29-2·77; p=0·0010), and high job strain (2·22, 1·59-3·09; p<0·0001) remained significant independent predictors of future onset of common mental disorder. If causality is assumed, our findings suggest that 14% of new cases of common mental disorder could have been prevented through elimination of high job strain (population attributable fraction 0·14, 0·06-0·20). High job strain appears to independently affect the risk of future common mental disorders in midlife. These findings suggest that modifiable work-related risk factors might be an important target in efforts to reduce the prevalence of common mental disorders. iCare Foundation and Mental Health Branch, NSW Health. Copyright © 2018 Elsevier Ltd. All rights reserved.

Combining evidence from multiple electronic health care databases: performances of one-stage and two-stage meta-analysis in matched case-control studies.

PubMed

La Gamba, Fabiola; Corrao, Giovanni; Romio, Silvana; Sturkenboom, Miriam; Trifirò, Gianluca; Schink, Tania; de Ridder, Maria

2017-10-01

Clustering of patients in databases is usually ignored in one-stage meta-analysis of multi-database studies using matched case-control data. The aim of this study was to compare bias and efficiency of such a one-stage meta-analysis with a two-stage meta-analysis. First, we compared the approaches by generating matched case-control data under 5 simulated scenarios, built by varying: (1) the exposure-outcome association; (2) its variability among databases; (3) the confounding strength of one covariate on this association; (4) its variability; and (5) the (heterogeneous) confounding strength of two covariates. Second, we made the same comparison using empirical data from the ARITMO project, a multiple database study investigating the risk of ventricular arrhythmia following the use of medications with arrhythmogenic potential. In our study, we specifically investigated the effect of current use of promethazine. Bias increased for one-stage meta-analysis with increasing (1) between-database variance of exposure effect and (2) heterogeneous confounding generated by two covariates. The efficiency of one-stage meta-analysis was slightly lower than that of two-stage meta-analysis for the majority of investigated scenarios. Based on ARITMO data, there were no evident differences between one-stage (OR = 1.50, CI = [1.08; 2.08]) and two-stage (OR = 1.55, CI = [1.12; 2.16]) approaches. When the effect of interest is heterogeneous, a one-stage meta-analysis ignoring clustering gives biased estimates. Two-stage meta-analysis generates estimates at least as accurate and precise as one-stage meta-analysis. However, in a study using small databases and rare exposures and/or outcomes, a correct one-stage meta-analysis becomes essential. Copyright © 2017 John Wiley & Sons, Ltd.

Cross-sectional analysis of food choice frequency, sleep confounding beverages, and psychological distress predictors of sleep quality.

PubMed

Knowlden, Adam P; Burns, Maranda; Harcrow, Andy; Shewmake, Meghan E

2016-03-16

Poor sleep quality is a significant public health problem. The role of nutrition in predicting sleep quality is a relatively unexplored area of inquiry. The purpose of this study was to evaluate the capacity of 10 food choice categories, sleep confounding beverages, and psychological distress to predict the sleep quality of college students. A logistic regression model comprising 10 food choice variables (healthy proteins, unhealthy proteins, healthy dairy, unhealthy dairy, healthy grains, unhealthy grains, healthy fruits and vegetables, unhealthy empty calories, healthy beverages, unhealthy beverages), sleep confounding beverages (caffeinated/alcoholic beverages), as well as psychological distress (low, moderate, serious distress) was computed to determine the capacity of the variables to predict sleep quality (good/poor). The odds of poor sleep quality were 32.4% lower for each unit of increased frequency of healthy proteins consumed (p<0.001; OR=0.676), 14.1% lower for each unit of increased frequency of healthy dairy food choices consumed (p=0.024; OR=0.859), 13.1% higher for each unit of increased frequency of empty calorie food choices consumed (p=0.003; OR=1.131), and 107.3% higher for those classified in the moderate psychological distress (p=0.016; OR=2.073). Collectively, healthy proteins, healthy dairy, unhealthy empty calories, and moderate psychological distress were moderately predictive of sleep quality in the sample (Nagelkerke R2=23.8%). Results of the study suggested higher frequency of consumption of healthy protein and healthy dairy food choices reduced the odds of poor sleep quality, while higher consumption of empty calories and moderate psychological distress increased the odds of poor sleep quality.

Five Steps to Successfully Implement and Evaluate Propensity Score Matching in Clinical Research Studies.

PubMed

Staffa, Steven J; Zurakowski, David

2018-01-09

In clinical research, the gold standard level of evidence is the randomized controlled trial (RCT). The availability of nonrandomized retrospective data is growing; however, a primary concern of analyzing such data is comparability of the treatment groups with respect to confounding variables. Propensity score matching (PSM) aims to equate treatment groups with respect to measured baseline covariates to achieve a comparison with reduced selection bias. It is a valuable statistical methodology that mimics the RCT, and it may create an "apples to apples" comparison while reducing bias due to confounding. PSM can improve the quality of anesthesia research and broaden the range of research opportunities. PSM is not necessarily a magic bullet for poor-quality data, but rather may allow the researcher to achieve balanced treatment groups similar to a RCT when high-quality observational data are available. PSM may be more appealing than the common approach of including confounders in a regression model because it allows for a more intuitive analysis of a treatment effect between 2 comparable groups.We present 5 steps that anesthesiologists can use to successfully implement PSM in their research with an example from the 2015 Pediatric National Surgical Quality Improvement Program: a validated, annually updated surgery and anesthesia pediatric database. The first step of PSM is to identify its feasibility with regard to the data at hand and ensure availability of data on any potential confounders. The second step is to obtain the set of propensity scores from a logistic regression model with treatment group as the outcome and the balancing factors as predictors. The third step is to match patients in the 2 treatment groups with similar propensity scores, balancing all factors. The fourth step is to assess the success of the matching with balance diagnostics, graphically or analytically. The fifth step is to apply appropriate statistical methodology using the propensity-matched data to compare outcomes among treatment groups.PSM is becoming an increasingly more popular statistical methodology in medical research. It often allows for improved evaluation of a treatment effect that may otherwise be invalid due to a lack of balance between the 2 treatment groups with regard to confounding variables. PSM may increase the level of evidence of a study and in turn increases the strength and generalizability of its results. Our step-by-step approach provides a useful strategy for anesthesiologists to implement PSM in their future research.

Identification and Sensitivity Analysis for Average Causal Mediation Effects with Time-Varying Treatments and Mediators: Investigating the Underlying Mechanisms of Kindergarten Retention Policy.

PubMed

Park, Soojin; Steiner, Peter M; Kaplan, David

2018-06-01

Considering that causal mechanisms unfold over time, it is important to investigate the mechanisms over time, taking into account the time-varying features of treatments and mediators. However, identification of the average causal mediation effect in the presence of time-varying treatments and mediators is often complicated by time-varying confounding. This article aims to provide a novel approach to uncovering causal mechanisms in time-varying treatments and mediators in the presence of time-varying confounding. We provide different strategies for identification and sensitivity analysis under homogeneous and heterogeneous effects. Homogeneous effects are those in which each individual experiences the same effect, and heterogeneous effects are those in which the effects vary over individuals. Most importantly, we provide an alternative definition of average causal mediation effects that evaluates a partial mediation effect; the effect that is mediated by paths other than through an intermediate confounding variable. We argue that this alternative definition allows us to better assess at least a part of the mediated effect and provides meaningful and unique interpretations. A case study using ECLS-K data that evaluates kindergarten retention policy is offered to illustrate our proposed approach.

Toward a clearer portrayal of confounding bias in instrumental variable applications.

PubMed

Jackson, John W; Swanson, Sonja A

2015-07-01

Recommendations for reporting instrumental variable analyses often include presenting the balance of covariates across levels of the proposed instrument and levels of the treatment. However, such presentation can be misleading as relatively small imbalances among covariates across levels of the instrument can result in greater bias because of bias amplification. We introduce bias plots and bias component plots as alternative tools for understanding biases in instrumental variable analyses. Using previously published data on proposed preference-based, geography-based, and distance-based instruments, we demonstrate why presenting covariate balance alone can be problematic, and how bias component plots can provide more accurate context for bias from omitting a covariate from an instrumental variable versus non-instrumental variable analysis. These plots can also provide relevant comparisons of different proposed instruments considered in the same data. Adaptable code is provided for creating the plots.

A Behavior Genetic Investigation of Adolescent Motherhood and Offspring Mental Health Problems

PubMed Central

Harden, K. Paige; Lynch, Stacy K.; Turkheimer, Eric; Emery, Robert E.; D’Onofrio, Brian M.; Slutske, Wendy S.; Waldron, Mary D.; Heath, Andrew C.; Statham, Dixie J.; Martin, Nicholas G.

2010-01-01

The present study examines the relations between adolescent motherhood and children’s behavior, substance use, and internalizing problems in a sample of 1,368 children of 712 female twins from Australia. Adolescent motherhood remained significantly associated with all mental health problems, even when using a quasiexperimental design capable of controlling for genetic and environmental confounds. However, the relation between adolescent motherhood and offspring behavior problems and substance use was partially confounded by family background variables that influence both generations. The results are consistent with a causal relation between adolescent motherhood and offspring mental health problems, and they highlight the usefulness of behavior genetic designs when examining putative environmental risks for the development of psychopathology. The generalizability of these results to the United States, which has a higher adolescent birth rate, is discussed. PMID:18020715

Model building strategy for logistic regression: purposeful selection.

PubMed

Zhang, Zhongheng

2016-03-01

Logistic regression is one of the most commonly used models to account for confounders in medical literature. The article introduces how to perform purposeful selection model building strategy with R. I stress on the use of likelihood ratio test to see whether deleting a variable will have significant impact on model fit. A deleted variable should also be checked for whether it is an important adjustment of remaining covariates. Interaction should be checked to disentangle complex relationship between covariates and their synergistic effect on response variable. Model should be checked for the goodness-of-fit (GOF). In other words, how the fitted model reflects the real data. Hosmer-Lemeshow GOF test is the most widely used for logistic regression model.

Exploring heterogeneity in clinical trials with latent class analysis

PubMed Central

Abarda, Abdallah; Contractor, Ateka A.; Wang, Juan; Dayton, C. Mitchell

2018-01-01

Case-mix is common in clinical trials and treatment effect can vary across different subgroups. Conventionally, a subgroup analysis is performed by dividing the overall study population by one or two grouping variables. It is usually impossible to explore complex high-order intersections among confounding variables. Latent class analysis (LCA) provides a framework to identify latent classes by observed manifest variables. Distal clinical outcomes and treatment effect can be different across these classes. This paper provides a step-by-step tutorial on how to perform LCA with R. A simulated dataset is generated to illustrate the process. In the example, the classify-analyze approach is employed to explore the differential treatment effects on distal outcomes across latent classes. PMID:29955579

Heart period variability and psychopathology in urban boys at risk for delinquency.

PubMed

Pine, D S; Wasserman, G A; Miller, L; Coplan, J D; Bagiella, E; Kovelenku, P; Myers, M M; Sloan, R P

1998-09-01

To examine associations between heart period variability (HPV) and psychopathology in young urban boys at risk for delinquency, a series of 697-11-year-old younger brothers of adjudicated delinquents received a standardized psychiatric evaluation and an assessment of heart period variability (HPV). Psychiatric symptoms were rated in two domains: externalizing and internalizing psychopathology. Continuous measures of both externalizing and internalizing psychopathology were associated with reductions in HPV components related to parasympathetic activity. These associations could not be explained by a number of potentially confounding variables, such as age, ethnicity, social class, body size, or family history of hypertension. Although familial hypertension predicted reduced HPV and externalizing psychopathology, associations between externalizing psychopathology and HPV were independent of familial hypertension. Psychiatric symptoms are associated with reduced HPV in young urban boys at risk for delinquency.

Beyond greening and browning: the need for an integrated understanding of Arctic change

NASA Astrophysics Data System (ADS)

Gamon, J. A.; Huemmrich, K. F.; Hmimina, G.; Yu, R.

2017-12-01

Satellite records and field observations povide contradictory evidence for "greening" or "browning" of Arctic tundra. Large-scale observations of apparent greening have been based on satellite vegetation indices (e.g NDVI). However, a clear interpretation of these trends are confounded by changing snow cover and surface hydrology, both of which influence NDVI and are known to be changing independently of any direct vegetation response. Field studies have demonstrated greening in some areas, but not others, and have also documented changing permafrost depth, surface hydrology and snow cover. Together, these confounding factors can explain some of the contradictory evidence based regarding greening and browning. Given the multiple influences on Arctic NDVI, simple conclusions regarding greening and browning from satellite data alone can be incorrect; when these confounding factors are taken into account, some areas that show apparent greening in the satellite record appear to be undergoing productivity declines due to surface drying. These contradictory interpretations have profound implications for our understanding of changing surface energy balance, biogeochemistry, and surface-atmosphere feedbacks. To better address Arctic ecosystem responses to a changing climate, an integrated, multi-scale, multivariate approach that considers hydrology, permafrost, snow cover and vegetation is needed.

Offspring ADHD as a Risk Factor for Parental Marital Problems: Controls for Genetic and Environmental Confounds

PubMed Central

Schermerhorn, Alice C.; D’Onofrio, Brian M.; Slutske, Wendy S.; Emery, Robert E.; Turkheimer, Eric; Harden, K. Paige; Heath, Andrew C.; Martin, Nicholas G.

2013-01-01

Background Previous studies have found that child attention-deficit/hyperactivity disorder (ADHD) is associated with more parental marital problems. The reasons for this association are unclear, however. The association might be due to genetic or environmental confounds that contribute to both marital problems and ADHD. Method Data were drawn from the Australian Twin Registry, including 1296 individual twins, their spouses, and offspring. We studied adult twins who were discordant for offspring ADHD. Using a discordant twin pairs design, we examined the extent to which genetic and environmental confounds, as well as measured parental and offspring characteristics, explain the ADHD-marital problems association. Results Offspring ADHD predicted parental divorce and marital conflict. The associations were also robust when comparing differentially exposed identical twins to control for unmeasured genetic and environmental factors, when controlling for measured maternal and paternal psychopathology, when restricting the sample based on timing of parental divorce and ADHD onset, and when controlling for other forms of offspring psychopathology. Each of these controls rules out alternative explanations for the association. Conclusion The results of the current study converge with those of prior research in suggesting that factors directly associated with offspring ADHD increase parental marital problems. PMID:22958575

Land-use change and infectious disease in West Africa

NASA Astrophysics Data System (ADS)

Thomson, M. C.; Ericksen, P. J.; Mohamed, A. Ben; Connor, S. J.

Land-use change has been associated with changes in the dynamics of infectious disease in West Africa. Here we describe the complex interactions of land-use change with three diseases (both vector- and non-vector-borne) of considerable public health significance in this region, namely, malaria and irrigation; epidemic meningitis and land degradation; onchocerciasis and deforestation. We highlight the confounding effect of climate variability, which acts as a driver of both land-use change and human health. We conclude, as have others, that the scale of observation always matters, and complex and dynamic feedbacks among social-ecological systems are not easily teased apart. We suggest that in order to establish the causal chain of interactions between land-use change and human health outcomes two approaches are necessary. The first is to have a thorough understanding of the aetiology of disease and the specific mechanisms by which land-use and climate variability affect the transmission of pathogens. This is achieved by focused, detailed studies encompassing a wide range of potential drivers, which are inevitably small scale and often cover short time periods. The second consists of large-scale studies of statistical associations between transmission indices or health outcomes and environmental variables stratified by known ecological or socio-economic confounders, and sufficient in size to overcome local biases in results. Such research activities need to be designed to inform each other if we are to develop predictive models for monitoring these diseases and to develop integrated programs for human health and sustainable land use.

Watching television for more than two hours increases the likelihood of reporting poor sleep quality among Brazilian schoolteachers.

PubMed

de Souza, Sara Carolina Scremin; Campanini, Marcela Zambrim; de Andrade, Selma Maffei; González, Alberto Durán; de Melo, Juliana Moura; Mesas, Arthur Eumann

2017-10-01

Although time spent watching television and sleep problems have increased in the last few decades, it is unclear whether these conditions are associated in working adults after controlling for lifestyle, job characteristics and other individual aspects. The present study analyzed the association between time spent watching television and sleep quality among teachers from public schools in Londrina, Brazil. In this cross-sectional study, information from the Pittsburgh Sleep Quality Index (PSQI) and about time spent watching television was obtained during personal interviews. Logistic regression models adjusted by the main confounders (sociodemographic, occupational and lifestyle variables) were used in the analyses. Among the 959 studied teachers (68.2% women, median age: 42years), teachers who watched >120min/day had a higher likelihood of reporting poor sleep quality (PSQI>5) (odds ratio=1.41; 95% confidence interval=1.01; 1.98) compared with those who watched television for up to 60min/day, regardless of gender, age, work hours, leisure time physical activity and other lifestyle variables. This association did not remain significant after the adjustment for health conditions, i.e., obesity, anxiety, depression and chronic pain, which may act as confounding variables in the relationship between watching television and poor sleep quality. Watching television for >120min/day was independently associated with poorer sleep quality, which should be considered in the prevention and treatment of sleep disturbances among working population. Copyright © 2017 Elsevier Inc. All rights reserved.

Brain tumors in children and occupational exposure of parents.

PubMed

Peters, F M; Preston-Martin, S; Yu, M C

1981-07-10

Ninety-two cases of brain tumor in children less than 10 years old were compared with 92 matched controls for parental occupational history. Cases were more likely than controls to show material occupations involving chemical exposure, paternal occupations involving solvents, and employment of father in the aircraft industry. These three factors were not affected by adjustment for the potential confounding variables examined in this study.

Thyroid disorders in older adults.

PubMed

Visser, W Edward; Visser, Theo J; Peeters, Robin P

2013-06-01

This article summarizes the current literature about serum thyroid parameters and thyroid disease during aging. Changes in thyroid function tests may be part of the physiology of aging, after exclusion of confounding variables. Overt thyroid disease requires immediate treatment. Treatment of subclinical hyperthyroidism in the elderly can be advocated, while watchful waiting may be an appropriate approach for subclinical hypothyroidism. Copyright © 2013 Elsevier Inc. All rights reserved.

The Effects of Fraternity and Sorority Membership in the Fourth Year of College: A Detrimental or Value-Added Component of Undergraduate Education?

ERIC Educational Resources Information Center

Hevel, Michael S.; Martin, Georgianna L.; Weeden, Dustin D.; Pascarella, Ernest T.

2015-01-01

We use a longitudinal national dataset to explore the direct and conditional effects of fraternity/sorority membership on students' educational outcomes in the 4th year of college. Controlling for a variety of potentially confounding variables, including pretest measures of the outcomes, we find no direct effect of fraternity/sorority membership…

An Assessment of the Influence of Attention to the Task in the Measurement of Visual Perceptual Abilities. Final Report.

ERIC Educational Resources Information Center

Rodenborn, Leo V., Jr.

The project's purpose was to determine whether attention to the task during testing was a confounding variable in measures of visual perception ability. Samples of 30 perceptually handicapped (PH) and 30 normal subjects (N) were randomly selected from children so classified on the Frostig DTVP, providing they had IQ scores between 85 and 115 on…

Sample size calculations for case-control studies

Cancer.gov

This R package can be used to calculate the required samples size for unconditional multivariate analyses of unmatched case-control studies. The sample sizes are for a scalar exposure effect, such as binary, ordinal or continuous exposures. The sample sizes can also be computed for scalar interaction effects. The analyses account for the effects of potential confounder variables that are also included in the multivariate logistic model.

Reducing the Language Content in ToM Tests: A Developmental Scale

ERIC Educational Resources Information Center

Burnel, Morgane; Perrone-Bertolotti, Marcela; Reboul, Anne; Baciu, Monica; Durrleman, Stephanie

2018-01-01

The goal of the current study was to statistically evaluate the reliable scalability of a set of tasks designed to assess Theory of Mind (ToM) without language as a confounding variable. This tool might be useful to study ToM in populations where language is impaired or to study links between language and ToM. Low verbal versions of the ToM tasks…

An evidence-based approach to globally assess the covariate-dependent effect of the MTHFR single nucleotide polymorphism rs1801133 on blood homocysteine: a systematic review and meta-analysis.

PubMed

Jin, Huifeng; Cheng, Haojie; Chen, Wei; Sheng, Xiaoming; Levy, Mark A; Brown, Mark J; Tian, Junqiang

2018-05-01

The single nucleotide polymorphism of the gene 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T (or rs1801133) is the most established genetic factor that increases plasma total homocysteine (tHcy) and consequently results in hyperhomocysteinemia. Yet, given the limited penetrance of this genetic variant, it is necessary to individually predict the risk of hyperhomocysteinemia for an rs1801133 carrier. We hypothesized that variability in this genetic risk is largely due to the presence of factors (covariates) that serve as effect modifiers, confounders, or both, such as folic acid (FA) intake, and aimed to assess this risk in the complex context of these covariates. We systematically extracted from published studies the data on tHcy, rs1801133, and any previously reported rs1801133 covariates. The resulting metadata set was first used to analyze the covariates' modifying effect by meta-regression and other statistical means. Subsequently, we controlled for this modifying effect by genotype-stratifying tHcy data and analyzed the variability in the risk resulting from the confounding of covariates. The data set contains data on 36 rs1801133 covariates that were collected from 114,799 participants and 256 qualified studies, among which 6 covariates (sex, age, race, FA intake, smoking, and alcohol consumption) are the most frequently informed and therefore included for statistical analysis. The effect of rs1801133 on tHcy exhibits significant variability that can be attributed to effect modification as well as confounding by these covariates. Via statistical modeling, we predicted the covariate-dependent risk of tHcy elevation and hyperhomocysteinemia in a systematic manner. We showed an evidence-based approach that globally assesses the covariate-dependent effect of rs1801133 on tHcy. The results should assist clinicians in interpreting the rs1801133 data from genetic testing for their patients. Such information is also important for the public, who increasingly receive genetic data from commercial services without interpretation of its clinical relevance. This study was registered at Research Registry with the registration number reviewregistry328.

Child maltreatment and educational attainment in young adulthood: results from the Ontario Child Health Study.

PubMed

Tanaka, Masako; Georgiades, Katholiki; Boyle, Michael H; MacMillan, Harriet L

2015-01-01

There is increasing evidence for the adverse effects of child maltreatment on academic performance; however, most of these studies used selective samples and did not account for potential confounding or mediating factors. We examined the relationship between child physical abuse (PA; severe and non-severe) and sexual abuse (SA) and educational attainment (years of education, failure to graduate from high school) with a Canadian community sample. We used data from the Ontario Child Health Study (N = 1,893), a province-wide longitudinal survey. Potential confounding variables (family socio-demographic and parental capacity) and child-level characteristics were assessed in 1983, and child abuse was determined in 2000-2001 based on retrospective self-report. Results showed that PA and SA were associated with several factors indicative of social disadvantage in childhood. Multilevel regression analyses for years of education revealed a significant estimate for severe PA based on the unadjusted model (-0.60 years, 95% CI = [-0.45, -0.76]); estimates for non-severe PA (0.05 years, CI = [-0.15, 0.26]) and SA (-0.25 years, CI = [-0.09, -0.42]) were not significant. In the adjusted full model, the only association to reach significance was between severe PA and reduced years of education (-0.31 years, CI = [-0.18, -0.44]). Multilevel regression analyses for failure to graduate from high school showed significant unadjusted estimates for severe PA (OR = 1.77, 95% CI = [1.21, 2.58]) and non-severe PA (OR = 1.61, CI = [1.01, 2.57]); SA was not associated with this outcome (OR = 1.40, CI = [0.94, 2.07]). In the adjusted full models, there were no significant associations between child abuse variables and failure to graduate. The magnitude of effect of PA on both outcomes was reduced largely by child individual characteristics. These findings generally support earlier research, indicating the adverse effects of child maltreatment on educational attainment. Of particular note, severe PA was associated with reduced years of education after accounting for a comprehensive set of potential confounding variables and child characteristics. © The Author(s) 2014.

Impact of singlehood during pregnancy on dietary intake and birth outcomes- a study in the Norwegian Mother and Child Cohort Study.

PubMed

Farbu, Jorunn; Haugen, Margaretha; Meltzer, Helle Margrete; Brantsæter, Anne Lise

2014-12-05

Little attention has been given to the impact of singlehood during pregnancy. The aim of this study was to examine the impact of marital status on diet during pregnancy and pregnancy outcome. The study population comprised 62,773 women participating in the Norwegian Mother and Child Cohort Study. Marital status was categorised into singles living alone, singles living with parents and married/cohabiting (reference group). Participants answered a general health questionnaire in gestational week 15-17 and a food frequency questionnaire in gestational week 22. We used nonparametric tests to compare dietary intakes by marital status, and multiple logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) for infants being small for gestational age (SGA), large for gestational age (LGA), and preterm delivery (defined as delivery before gestational week 37). Single women living with parents had lower intakes of fruits and vegetables, higher intake of total energy, higher proportion of energy from added sugar, and lower intake of fibre than the reference group. Singles living alone also had a higher intake of added sugar. In both of the single groups, daily smoking was more prevalent than in women living with a partner. In analyses adjusted for maternal age, pre-pregnancy BMI, energy intake, energy contributed by protein, education, income, parity and nausea, single women living alone had increased risk of SGA with OR = 1.27 (95% CI: 1.05, 1.55). When smoking was included among the confounding variables, the association was no longer significant. Likewise, singles living alone had increased risk of preterm delivery, with OR = 1.32 (95% CI: 1.01, 1.72) in a partly adjusted model, but the association did not remain significant in a model fully adjusted for confounding variables. Single mothers had lower dietary quality and included more smokers than women who lived with a partner. Single mothers living alone had higher prevalence of SGA and preterm delivery, but the associations with adverse pregnancy outcomes were confounded by other variables. This study shows that single mothers should be given special attention during antenatal care and counselling.

Predictors of Hyporesponsiveness to Erythropoiesis-Stimulating Agents in Hemodialysis Patients

PubMed Central

Kalantar-Zadeh, Kamyar; Lee, Grace H; Miller, Jessica E.; Streja, Elani; Jing, Jennie; Robertson, John A; Kovesdy, Csaba P.

2009-01-01

Background Identification of predictors of hyporesponsiveness to erythropoietin-stimulating agents (ESA) in hemodialysis (HD) patients may help improve anemia management and reduce hemoglobin variability. Study Design We conducted repeated measure and logistic regression analyses in a retrospective cohort of long-term HD patients to examine the association of iron markers and measures of renal osteodystrophy with ESA-responsiveness. The ESA-response coefficient at the individual level, i.e., the least-confounded dose-response association, was separated from the population level, assumed to represent confounding by medical indication. Setting/Participants The national database of a large dialysis organization (DaVita) with 38,328 surviving prevalent HD patients over 12 months, who received ESA for at least 3 consecutive calendar quarters, was examined. Predictors Serum levels of ferritin, iron saturation ratio (ISAT), intact parathyroid hormone (PTH) and alkaline phosphatase levels. Outcomes/Other Measurements The main outcome was case-mix adjusted hemoglobin response to quarterly averaged ESA dose at individual level. The odds ratio (OR) of the greatest vs. poorest ESA-response quartile at patient level was calculated. OR<1.0 indicated ESA hyporesponsiveness and OR>1.0 enhanced responsiveness. Results The mean (±SD) ESA-response coefficients of the least to most responsive quartiles were 0.301±0.033, 0.344±0.004, 0.357±0.004, and 0.389±0.026 g/dL higher hemoglobin per 1,000 units/week higher ESA dose in each quarter, respectively. The ORs of the greatest vs. poorest ESA-responsiveness at patient level were the following: Serum ferritin<200 ng/ml: 0.77 [95% confidence interval: 0.70–0.86] (reference: 200–500 ng/ml), ISAT<20%: 0.54 [0.49–0.59] (reference: 20–30%), intact PTH≥600 pg/ml: 0.54 [0.49–0.60] (reference: 150–300 pg/ml), and alkaline phosphatase ≥160 IU/L: 0.64 [0.58–0.70] (reference: 80–120 IU/L). Lower estimated dietary protein intake and serum levels of nutritional markers were also associated with higher risk of ESA-hyporesponsiveness. Limitations Our results may incorporate uncontrolled confounding. Achieved hemoglobin may have different associations than targeted hemoglobin. Conclusions In long-term HD patients, low iron stores, hyperparathyroidism and high turnover bone disease are associated with significant ESA-hyporesponsiveness. Prospective studies are needed to verify these associations. PMID:19339087

Diet and lifestyle factors associated with fish consumption in men and women: a study of whether gender differences can result in gender-specific confounding

PubMed Central

2012-01-01

Background Fish consumption and intake of omega-3 fatty acids from fish are associated with a lower risk of cardiovascular disease. However, a prospective study from northern Sweden showed that high consumption of fish is associated with an increased risk of stroke in men, but not in women. The current study aimed to determine if fish consumption is differently related to lifestyle in men compared with women in northern Sweden. Methods Lifestyle information on 32,782 men and 34,866 women (aged 30–60 years) was collected between 1992 and 2006 within the Västerbotten Intervention Programme (a health intervention in northern Sweden). Spearman correlations coefficients (Rs) were calculated between self-reported consumption of fish and other food items. Lifestyle variables were compared between fish consumption categories. Results Fish consumption was positively associated with other foods considered healthy (e.g., root vegetables, lettuce/cabbage/spinach/broccoli, chicken, and berries; Rs = 0.21-0.30), as well as with other healthy lifestyle factors (e.g., exercise and not smoking) and a higher educational level, in both men and women. The only gender difference found, concerned the association between fish consumption and alcohol consumption. Men who were high consumers of fish had a higher intake of all types of alcohol compared with low to moderate fish consumers. For women, this was true only for wine. Conclusions Except for alcohol, the association between fish consumption and healthy lifestyle did not differ between men and women in northern Sweden. It is important to adjust for other lifestyle variables and socioeconomic variables in studies concerning the effect of fish consumption on disease outcome. PMID:23210480

The pulse-mass index as a predictor of cardiovascular events in women with systemic lupus erythematosus.

PubMed

García-Villegas, Elsy Aidé; Márquez-González, Horacio; Flores-Suárez, Luis Felipe; Villa-Romero, Antonio Rafael

2017-01-20

Patients with systemic lupus erythematosus (SLE) have 3times the risk of death compared to the rest of the population, with cardiovascular events (CVD) being one of the main causes. Índices such as waist-height (W-Ht I), waist-hip (W-Hp I) and pulse-mass (PMI) predict CVD, though the behaviour is unknown in patients with SLE. The aim of this study was to determine the prognostic value of PMI in the development of CVD in premenopausal women with SLE. Cohort study. Included were premenopausal women with SLE without prior CVD; excluded were those patients with antiphospholipid syndrome (APS), pregnancy, thyroid disease, recent liposuction, and chronic kidney disease. Exposure variables were: PMI, W-Ht I, W-Hp I and metabolic syndrome at onset of the cohort. Considered confounding variables were time of evolution, disease activity, cumulative damage and treatment. Through semi-annual appointments, accident and emergency admittance and hospitalisation records the CVD were screened. Analysis was performed with Cox for proportional hazards and survival with Kaplan Meier. We included 238 women with a median age of 31 (18-52) years, with a follow-up of 8years. We identified 22 (9.6%) cases of CVD. In the Cox proportional hazards analysis, the prognostic variables were: PMI with HR=8.1 (95% CI: 1.1-65), metabolic syndrome with 2.4 (95% CI: 1-5.8), cumulative damage with HR=1.5 (95% CI: 1.1-2.2) and body fat percentage HR=2.8 (95% CI: 1.1-6.9) CONCLUSIONS: The PMI is a better predictor factor of CVD in women with SLE. Copyright © 2016 Elsevier España, S.L.U. All rights reserved.

Prevalence and factors associated with sedentary behavior in adolescents

PubMed Central

Dias, Paula Jaudy Pedroso; Domingos, Isabela Prado; Ferreira, Márcia Gonçalves; Muraro, Ana Paula; Sichieri, Rosely; Gonçalves-Silva, Regina Maria Veras

2014-01-01

OBJECTIVE To analyze the prevalence of sedentary behavior and associated factors in adolescents. METHODS A cross-sectional study with adolescents aged 10 to 17 years, of both sexes, belonging to a 1994-1999 birth cohort in the city of Cuiabá, MT, Central Western Brazil. Data were collected using a questionnaire containing sociodemographic, economic, lifestyle and anthropometric variables. Sedentary behavior was determined as using television and/or computer/video games for a time greater than or equal to 4 hours/day. Associations with sedentary behavior were evaluated using body mass index in childhood and adolescence and sociodemographic and behavioral variables using hierarchical logistic regression. RESULTS The overall prevalence of sedentary behavior was 58.1%. Of the 1,716 adolescents evaluated, 50.7% (n = 870) were male. In multivariate analysis, after adjustment for confounding factors, the variables that remained associated with sedentary behavior were: age (14 and over) (OR = 3.51, 95%CI 2.19;5.60); higher socioeconomic class (OR = 3.83, 95%CI 2.10;7.01), higher level of maternal education (OR = 1.81, 95%CI 1.09;3.01); living in the country (OR = 0.49, 95%CI 0.30;0.81); insufficient physical activity (OR = 1.25, 95%CI 1.02;1.53); experimentation with alcoholic beverages (OR = 1.34, 95%CI 1.08;1.66) and being overweight in adolescence (OR = 1.33, 95%CI 1.06;1.68). CONCLUSIONS The high proportion of adolescents in sedentary activities and the lack of association with being overweight in childhood, indicates the need for educational initiatives to reduce multiple risk behaviors. Encouraging physical activity in young people as a way of reducing sedentary behavior and, consequently, being overweight is fundamental. PMID:24897048

Effects of diazoxide in multiple sclerosis

PubMed Central

Rovira, Alex; Montalban, Xavier; Arroyo, Rafael; Paul, Friedemann; Meca-Lallana, Virginia; Ramo, Cristina; Fernandez, Oscar; Saiz, Albert; Garcia-Merino, Antonio; Ramió-Torrentà, Lluís; Casanova, Bonaventura; Oreja-Guevara, Celia; Muñoz, Delicias; Martinez-Rodriguez, Jose Enrique; Lensch, Eckart; Prieto, Jose Maria; Meuth, Sven G.; Nuñez, Xavier; Campás, Clara; Pugliese, Marco

2015-01-01

Objective: The aim of this study was to test the safety of diazoxide and to search for signs of efficacy in patients with relapsing-remitting multiple sclerosis (RRMS). Methods: In this multicenter, randomized, placebo-controlled, double-blind trial (treatment allocation was concealed), 102 patients with RRMS were randomized to receive a daily oral dose of diazoxide (0.3 and 4 mg/d) or placebo for 24 weeks (NCT01428726). The primary endpoint was the cumulative number of new T1 gadolinium-enhancing lesions per patient, recorded every 4 weeks from week 4 to week 24. Secondary endpoints included brain MRI variables such as the number of new/enlarging T2 lesions and the percentage brain volume change (PBVC); clinical variables such as the percentage of relapse-free patients, relapse rate, and change in the Expanded Disability Status Scale score; and safety and tolerability. Results: Diazoxide was well-tolerated and it produced no serious adverse events other than 1 case of Hashimoto disease. At the 2 doses tested, diazoxide did not improve the primary endpoint or the MRI and clinical variables related to the presence of new lesions or relapses. Patients treated with diazoxide showed reduced PBVC compared with the placebo group, although such changes could be confounded by the higher disease activity of the treated group and the vascular effects of diazoxide. Conclusion: At the doses tested, oral diazoxide did not decrease the appearance of new lesions evident by MRI. The effects in slowing the progression of brain atrophy require further validation. Classification of evidence: This study provides Class I evidence that for patients with RRMS, diazoxide (0.3 and 4 mg/d) does not significantly change the number of new MRI T1 gadolinium-enhancing lesions. PMID:26405686

Depressive Symptoms and Heart Rate Variability: Evidence for a Shared Genetic Substrate in a Study of Twins

PubMed Central

Vaccarino, Viola; Lampert, Rachel; Bremner, J. Douglas; Lee, Forrester; Su, Shaoyong; Maisano, Carisa; Murrah, Nancy V.; Jones, Linda; Jawed, Farhan; Afzal, Nadeem; Ashraf, Ali; Goldberg, Jack

2018-01-01

Objective To clarify the relationship between depression and heart rate variability (HRV) in a sample of twins. Reduced HRV, a measure of autonomic dysfunction, has been linked to depression but many studies have inadequately controlled for familial and environmental factors. Furthermore, little is known about whether depression and HRV share common genetic pathways. Methods We performed power spectral analysis on 24-hour ambulatory electrocardiograms in 288 middle-aged male twins. Log-normalized ultra low, very low, low, high frequency, and total power were calculated. A lifetime history of major depressive disorder (MDD) was determined, using the Structured Clinical Interview for Psychiatry Disorders, and current depressive symptoms were measured with the Beck Depression Inventory. Mixed-effect regression models were used to account for intrapair variability and estimate within-pair effects at the same time controlling for potential confounders. Results Both current depressive symptoms and a history of MDD were significantly associated with lower HRV. There was a graded effect, and power in each frequency band was 29% to 36% lower in the lowest band compared with the highest BDI category. All HRV measures except high frequency remained significantly associated with current depressive symptoms in multivariable analysis, but not with lifetime history of MDD. When analyses were stratified by zygosity, a significant within-pair association between BDI score and HRV was found in the dizygotic but not in the monozygotic twins, suggesting a genetic influence on the association. Conclusions A shared, genetically influenced biological pathway underlies the association between depression and lower HRV. These two phenotypes may be the expression of a generalized neurobiological perturbation. PMID:18606724

Sleep and motor learning: Is there room for consolidation?

PubMed

Pan, Steven C; Rickard, Timothy C

2015-07-01

It is widely believed that sleep is critical to the consolidation of learning and memory. In some skill domains, performance has been shown to improve by 20% or more following sleep, suggesting that sleep enhances learning. However, recent work suggests that those performance gains may be driven by several factors that are unrelated to sleep consolidation, inviting a reconsideration of sleep's theoretical role in the consolidation of procedural memories. Here we report the first comprehensive investigation of that possibility for the case of motor sequence learning. Quantitative meta-analyses involving 34 articles, 88 experimental groups and 1,296 subjects confirmed the empirical pattern of a large performance gain following sleep and a significantly smaller gain following wakefulness. However, the results also confirm strong moderating effects of 4 previously hypothesized variables: averaging in the calculation of prepost gain scores, build-up of reactive inhibition over training, time of testing, and training duration, along with 1 supplemental variable, elderly status. With those variables accounted for, there was no evidence that sleep enhances learning. Thus, the literature speaks against, rather than for, the enhancement hypothesis. Overall there was relatively better performance after sleep than after wakefulness, suggesting that sleep may stabilize memory. That effect, however, was not consistent across different experimental designs. We conclude that sleep does not enhance motor learning and that the role of sleep in the stabilization of memory cannot be conclusively determined based on the literature to date. We discuss challenges and opportunities for the field, make recommendations for improved experimental design, and suggest approaches to data analysis that eliminate confounds due to averaging over online learning. (PsycINFO Database Record (c) 2015 APA, all rights reserved).

Correlation of Vitamin D status and orthodontic-induced external apical root resorption

PubMed Central

Tehranchi, Azita; Sadighnia, Azin; Younessian, Farnaz; Abdi, Amir H.; Shirvani, Armin

2017-01-01

Background: Adequate Vitamin D is essential for dental and skeletal health in children and adult. The purpose of this study was to assess the correlation of serum Vitamin D level with external-induced apical root resorption (EARR) following fixed orthodontic treatment. Materials and Methods: In this cross-sectional study, the prevalence of Vitamin D deficiency (defined by25-hydroxyvitamin-D) was determined in 34 patients (23.5% male; age range 12–23 years; mean age 16.63 ± 2.84) treated with fixed orthodontic treatment. Root resorption of four maxillary incisors was measured using before and after periapical radiographs (136 measured teeth) by means of a design-to-purpose software to optimize data collection. Teeth with a maximum percentage of root resorption (%EARR) were indicated as representative root resorption for each patient. A multiple linear regression model and Pearson correlation coefficient were used to assess the association of Vitamin D status and observed EARR. P < 0.05 was considered statistically significant. Results: The Pearson coefficient between these two variables was determined about 0.15 (P = 0.38). Regression analysis revealed that Vitamin D status of the patients demonstrated no significant statistical correlation with EARR, after adjustment of confounding variables using linear regression model (P > 0.05). Conclusion: This study suggests that Vitamin D level is not among the clinical variables that are potential contributors for EARR. The prevalence of Vitamin D deficiency does not differ in patients with higher EARR. These data suggest the possibility that Vitamin D insufficiency may not contribute to the development of more apical root resorption although this remains to be confirmed by further longitudinal cohort studies. PMID:29238379

Secondhand tobacco smoke exposure and pulmonary function: a cross-sectional study among non-smoking employees of bar and restaurants in Santiago, Chile

PubMed Central

Parro, Javiera; Aceituno, Paulina; Droppelmann, Andrea; Mesías, Sthepanie; Muñoz, Claudio; Marchetti, Nella; Iglesias, Verónica

2017-01-01

Introduction The workplace remains a significant source of secondhand smoke (SHS) exposure. This pollutant is known to be associated with respiratory and cardiovascular problems, but its effects on specific pulmonary function parameters remain largely unexplored. The objectives of this study were to measure SHS exposure among non-smoking employees of bar and restaurants in Santiago, Chile and to evaluate the effects of such exposure on pulmonary function. Methods Cross-sectional design. The study sample included non-smoking workers from 57 restaurants and bars in Santiago, Chile. The outcome variable was pulmonary function and the exposure variables were urine cotinine concentration, a biomarker for current SHS exposure, and years of SHS exposure in the workplace as proxy of chronic exposure. Personal and occupational variables were also recorded. Data analysis was performed using linear regression models adjusted by confounders. Results The median age of the workers was 35 years and the median employment duration at the analysed venues was 1 year. Workers in smoking facilities reported greater SHS exposure (36 hours per week) than workers in smoke-free locations (4 hours per week). Urine cotinine levels were inversely correlated with forced vital capacity, but the finding was not statistically significant (β=−0.0002; 95% CI −0.007 to 0.006). Years of exposure to SHS showed to be significantly associated with forced expiratory flow25/75 (β=−0.006; 95% CI −0.010 to −0.0004). Conclusion These findings suggest that cumulative exposure to SHS at work may contribute to deterioration of pulmonary function in non-smoking employees. PMID:28988182

Factors associated with disease expression patterns in systemic lupus erythematosus patients: results from LUMINA (LXXVII), a multiethnic US cohort.

PubMed

Ugarte-Gil, M F; Pimentel-Quiroz, V R; Vilá, L M; Reveille, J D; McGwin, G; Alarcón, G S

2017-05-01

Objective The objective of this study was to determine the association of disease expression patterns with demographic and clinical characteristics in SLE. Methods Patients from a multi-ethnic SLE cohort were included. Disease expression patterns were defined as acute SLE and insidious SLE; this group was divided into those who accrued three ACR criteria and then accrued the fourth (insidious pattern A) and those who have one or two and then accrued four criteria (insidious pattern B). Disease activity was ascertained with the SLAM-R and disease damage with SLICC/ACR damage index. Variables were compared using analysis of variance for numeric variables and χ 2 for categorical variables. Multivariable analyses adjusting for possible confounders were performed. Results Six hundred and forty patients were included; the most frequent pattern was the insidious pattern B, with 415 (64.8%) patients, followed by the acute SLE group with 115 (18.0%) and the insidious pattern A with 110 (17.2%) patients. Patients from the insidious pattern A were older at diagnosis (pattern A: 39.8 vs pattern B: 36.7 vs acute: 32.4 years; p < 0.0001), more educated (13.6 vs 13.1 vs 12.1; p = 0.0008) and with a less active disease at baseline (8.8 vs 9.2 vs 10.7; p = 0.0227). Caucasian and Hispanic (Puerto Rico) ethnicities were overrepresented in this group (40.0% vs 27.7% vs 19.1% and 18.2% vs 17.1% vs 9.6%; p = 0.0003). Conclusions More insidious onset is associated with older age, Caucasian ethnicity, higher level of education, and lower disease activity than those with acute onset. However, after multivariable analyses, disease activity was not associated with any disease expression pattern.

Terminal illness and the increased mortality risk of conventional antipsychotics in observational studies: a systematic review.

PubMed

Luijendijk, Hendrika J; de Bruin, Niels C; Hulshof, Tessa A; Koolman, Xander

2016-02-01

Numerous large observational studies have shown an increased risk of mortality in elderly users of conventional antipsychotics. Health authorities have warned against use of these drugs. However, terminal illness is a potentially strong confounder of the observational findings. So, the objective of this study was to systematically assess whether terminal illness may have biased the observational association between conventional antipsychotics and risk of mortality in elderly patients. Studies were searched in PubMed, CINAHL, Embase, the references of selected studies and articles referring to selected studies (Web of Science). Inclusion criteria were (i) observational studies that estimated (ii) the risk of all-cause mortality in (iii) new elderly users of (iv) conventional antipsychotics compared with atypical antipsychotics or no use. Two investigators assessed the characteristics of the exposure and reference groups, main results, measured confounders and methods used to adjust for unmeasured confounders. We identified 21 studies. All studies were based on administrative medical and pharmaceutical databases. Sicker and older patients received conventional antipsychotics more often than new antipsychotics. The risk of dying was especially high in the first month of use, and when haloperidol was administered per injection or in high doses. Terminal illness was not measured in any study. Instrumental variables that were used were also confounded by terminal illness. We conclude that terminal illness has not been adjusted for in observational studies that reported an increased risk of mortality risk in elderly users of conventional antipsychotics. As the validity of the evidence is questionable, so is the warning based on it. Copyright © 2015 John Wiley & Sons, Ltd.

Psychotic experiences and risk of self-injurious behaviour in the general population: a systematic review and meta-analysis.

PubMed

Honings, S; Drukker, M; Groen, R; van Os, J

2016-01-01

Recent studies suggest that psychotic experiences (PE) in the general population are associated with an increased risk of self-injurious behaviour. Both the magnitude of this association and the level of adjustment for confounders vary among studies. A meta-analysis was performed to integrate the available evidence. The influence of possible confounders, including variably defined depression, was assessed. A systematic review and meta-analysis was conducted including general population studies reporting on the risk of self-injurious behaviour in individuals with PE. Studies were identified by a systematic search strategy in Pubmed, PsycINFO and Embase. Reported effect sizes were extracted and meta-analytically pooled. The risk of self-injurious behaviour was 3.20 times higher in individuals with PE compared with those without. Subanalyses showed that PE were associated with self-harm, suicidal ideation as well as suicidal attempts. All studies had scope for considerable residual confounding; effect sizes adjusted for depression were significantly smaller than effect sizes unadjusted for depression. In the longitudinal studies, adjustment for psychopathology resulted in a 74% reduction in excess risk. PE are associated with self-injurious behaviour, suggesting they have potential as passive markers of suicidality. However, the association is confounded and several methodological issues remain, particularly how to separate PE from the full range of connected psychopathology in determining any specific association with self-injurious behaviour. Given evidence that PE represent an indicator of severity of non-psychotic psychopathology, the association between PE and self-injurious behaviour probably reflects a greater likelihood of self-injurious behaviour in more severe states of mental distress.

Factors associated with the choice of general medicine as a career among Japanese medical students

PubMed Central

Kawamoto, Ryuichi; Ninomiya, Daisuke; Kasai, Yoshihisa; Kusunoki, Tomo; Ohtsuka, Nobuyuki; Kumagi, Teru; Abe, Masanori

2016-01-01

Background In Japan, there is a shortage of young physicians in various specialties; the present situation of general medicine or family medicine (GM/FM) in particular is risky. The factors influencing the career choice of Japanese medical students are poorly understood. This study aims to identify factors related to choosing GM/FM as a career. Methods The study was designed as a cross-sectional survey. Students at one medical school in Japan filled out a questionnaire. Students were asked to state their intended medical specialty, and they rated the importance of specific individual and occupational aspects using a 4-point likert scale. Factor analysis was performed on the variables. Reliability of the factor scores was estimated using Cronbach‘s alpha coefficients; biserial correlations between the factors and career choices were calculated. Furthermore, multiple linear regression analysis was performed using career choice (GM/FM vs. others) as the criterion variable and the factors plus demographic characteristics as confounding variables. Results Factor analysis produced six factors that explained future career plans. Medical students in this study had a positive and realistic idea about GM/FM, but only 18.8% of them chose GM/FM first as a career. The significant variables associated with choosing GM/FM first as a career were: ‘Admission from hometown’ (β=0.189, P=0.001), ‘Student preparing for the entrance exam’ (β=0.172; P=0.001), ‘Intent for rural practice’ (β=0.123, P=0.016), and ‘Work–life balance’ (β=0.126, P=0.013). While significant variables that were negatively associated with choosing GM/FM were ‘Presence of medical relatives’ (β=−0.107, P=0.037) and ‘Scientific orientation’ (β=−0.125, P=0.013). Conclusions Strategies have been suggested, such as recruiting medical students with significant variables that were associated with choosing GM/FM first as a career. By engaging students early in their choice of career, we may be able to increase enthusiasm for this specialty. PMID:27172894

Striatal action-value neurons reconsidered.

PubMed

Elber-Dorozko, Lotem; Loewenstein, Yonatan

2018-05-31

It is generally believed that during economic decisions, striatal neurons represent the values associated with different actions. This hypothesis is based on studies, in which the activity of striatal neurons was measured while the subject was learning to prefer the more rewarding action. Here we show that these publications are subject to at least one of two critical confounds. First, we show that even weak temporal correlations in the neuronal data may result in an erroneous identification of action-value representations. Second, we show that experiments and analyses designed to dissociate action-value representation from the representation of other decision variables cannot do so. We suggest solutions to identifying action-value representation that are not subject to these confounds. Applying one solution to previously identified action-value neurons in the basal ganglia we fail to detect action-value representations. We conclude that the claim that striatal neurons encode action-values must await new experiments and analyses. © 2018, Elber-Dorozko et al.

Residential proximity to industrial sites in the area of Taranto (Southern Italy). A case-control cancer incidence study.

PubMed

Marinaccio, Alessandro; Belli, Stefano; Binazzi, Alessandra; Scarselli, Alberto; Massari, Stefania; Bruni, Antonella; Conversano, Michele; Crosignani, Paolo; Minerba, Aldo; Zona, Amerigo; Comba, Pietro

2011-01-01

The association between cancer incidence and the residence near polluting facilities in an industrial area nearby Taranto has been investigated. Age, sex and occupational exposure were controlled as confounding variables in a case-control study (658 cases, 2092 controls). High risks were evidenced close to the steel mill (OR: 3.54), coke plant (OR: 4.80), mineral deposit (OR: 3.33) and shipbuilding (OR: 4.29) for pleural neoplasm, and to the steel mill (OR: 1.65) and shipbuilding (OR: 1.79) for lung cancer. After adjustment for occupational exposure, increasing trends of risk were observed both for lung and bladder cancers. Cancer risks were evidenced near industrial sites and the introduction of "occupational exposure" as a confounder modified significantly the risks with respect to distance from the source of pollution, particularly for pleural, lung and bladder cancers.

Memory Test Performance on Analogous Verbal and Nonverbal Memory Tests in Patients with Frontotemporal Dementia and Alzheimer's Disease.

PubMed

Baldock, Deanna; Miller, Justin B; Leger, Gabriel C; Banks, Sarah Jane

2016-01-01

Patients with frontotemporal dementia (FTD) typically have initial deficits in language or changes in personality, while the defining characteristic of Alzheimer's disease (AD) is memory impairment. Neuropsychological findings in the two diseases tend to differ, but can be confounded by verbal impairment in FTD impacting performance on memory tests in these patients. Twenty-seven patients with FTD and 102 patients with AD underwent a neuropsychological assessment before diagnosis. By utilizing analogous versions of a verbal and nonverbal memory test, we demonstrated differences in these two modalities between AD and FTD. Better differentiation between AD and FTD is found in a nonverbal memory test, possibly because it eliminates the confounding variable of language deficits found in patients with FTD. These results highlight the importance of nonverbal learning tests with multiple learning trials in diagnostic testing.

No Evidence of Sex-Related Survival Disparities among Head and Neck Cancer Patients Receiving Similar Multidisciplinary Care: A Matched-Pair Analysis

PubMed Central

Roberts, Jess C.; Li, Guojun; Reitzel, Lorraine R.; Wei, Qingyi; Sturgis, Erich M.

2010-01-01

Purpose It is unknown whether there are survival disparities between men and women with squamous cell carcinoma of the head and neck (SCCHN), though some data suggest that men have worse outcomes. We conducted a matched-pair study that controlled for several potentially confounding prognostic variables to assess whether a survival advantage exists for female compared with male SCCHN patients receiving similar care. Experimental Design We selected 286 female patients and 286 matched male patients from within a prospective epidemiologic study of 1654 patients with incident SCCHN evaluated and treated at a single large multidisciplinary cancer center. Matching variables included age (± 10 years), race/ethnicity, smoking status (never versus ever), tumor site (oral cavity versus oropharynx versus larynx versus hypopharynx), tumor classification (T1–2 versus T3–4), nodal status (negative versus positive), and treatment (surgery, radiation therapy, surgery and radiation therapy, surgery and chemotherapy, chemoradiotherapy, or surgery and chemoradiotherapy). Results Matched-pair and log-rank analyses showed no significant differences between women and men in recurrence-free, disease-specific, or overall survival. When the analysis was restricted to individual sites (oral cavity, oropharynx, or larynx/hypopharynx), there was also no evidence of a disparity in survival associated with sex. Conclusions We conclude that there is no evidence to suggest that a survival advantage exists for women as compared to men with SCCHN receiving similar multidisciplinary directed care at a tertiary cancer center. PMID:20943762

Outcomes of Extremely Low Birth Weight Infants with Acidosis at Birth

PubMed Central

Randolph, David A.; Nolen, Tracy L.; Ambalavanan, Namasivayam; Carlo, Waldemar A.; Peralta-Carcelen, Myriam; Das, Abhik; Bell, Edward F.; Davis, Alexis S.; Laptook, Abbot R.; Stoll, Barbara J.; Shankaran, Seetha; Higgins, Rosemary D.

2014-01-01

OBJECTIVES To test the hypothesis that acidosis at birth is associated with the combined primary outcome of death or neurodevelopmental impairment (NDI) in extremely low birth weight (ELBW) infants, and to develop a predictive model of death/NDI exploring perinatal acidosis as a predictor variable. STUDY DESIGN The study population consisted of ELBW infants born between 2002-2007 at NICHD Neonatal Research Network hospitals. Infants with cord blood gas data and documentation of either mortality prior to discharge or 18-22 month neurodevelopmental outcomes were included. Multiple logistic regression analysis was used to determine the contribution of perinatal acidosis, defined as a cord blood gas with a pH<7 or base excess (BE)<-12, to death/NDI in ELBW infants. In addition, a multivariable model predicting death/NDI was developed. RESULTS 3979 patients were identified of whom 249 had a cord gas pH<7 or BE<-12 mEq/L. 2124 patients (53%) had the primary outcome of death/NDI. After adjustment for confounding variables, pH<7 and BE<-12 mEq/L were each significantly associated with death/NDI (OR=2.5[1.6,4.2]; and OR=1.5[1.1,2.0], respectively). However, inclusion of pH or BE did not improve the ability of the multivariable model to predict death/NDI. CONCLUSIONS Perinatal acidosis is significantly associated with death/NDI in ELBW infants. Perinatal acidosis is infrequent in ELBW infants, however, and other factors are more important in predicting death/NDI. PMID:24554564

Prevalence of sedentary behavior and its correlates among primary and secondary school students

PubMed Central

Ferreira, Rodrigo Wiltgen; Rombaldi, Airton José; Ricardo, Luiza Isnardi Cardoso; Hallal, Pedro Curi; Azevedo, Mario Renato

2016-01-01

Abstract Objective: To determine the students’ exposure to four different sedentary behavior (SB) indicators and their associations with gender, grade, age, economic status and physical activity level. Methods: A cross-sectional study was conducted in 2013. The SB was collected using the HELENA instrument, composed by screen time questions (TV, video games and internet) and sitting activities on school opposite shift. The cut point of ≥2h/day was used to categorize the outcome. The Poisson regression was used for associations between the outcome and the independent variables (95% significance level), controlling for confounding variables and the possible design effect. Results: The sample was composed by 8661 students. The overall prevalence of SB was 69.2% (CI95% 68.1–70.2) on weekdays, and 79.6% (CI95% 78.7–80.5) on weekends. Females were more associated with the outcome, except to electronic games. Advanced grades students were more involved in sitting tasks when compared to the early grades. Older students were more likely to surf on net for ≥2h/day. Higher economic level students were more likely to engage in video games and internet. Active individuals were less likely to engage in SB on weekdays. Conclusions: The prevalence of SB was high, mainly on weekends. The associations with sex, age, grade and physical activity level should be considered into elaboration of more efficient interventions on SB control. PMID:26826878

Gender Inequality in the Couple Relationship and Leisure-Based Physical Exercise

PubMed Central

Annandale, Ellen; Hammarström, Anne

2015-01-01

Aims To analyse whether gender inequality in the couple relationship was related to leisure-based physical activity, after controlling for earlier physical activity and confounders. Methods Data drawn from the Northern Swedish Cohort of all pupils in their final year of compulsory schooling in a town in the North of Sweden. The sample consisted of 772 respondents (n = 381 men, n = 391 women) in the 26-year follow-up (in 2007, aged 42) who were either married or cohabiting. Ordinal regression, for men and women separately, was used to assess the association between gender inequality (measured as self-perceived equality in the couple relationship using dummy variables) and a measure of exercise frequency, controlling for prior exercise frequency, socioeconomic status, the presence of children in the home, and longer than usual hours in paid work. Results The perception of greater gender equality in the couple relationship was associated with higher levels of physical activity for both men and women. This remained significant when the other variables were controlled for. Amongst men the confidence intervals were high. Conclusions The results point to the potential of perceived gender equality in the couple relationship to counteract the general time poverty and household burden that often arises from the combination of paid work and responsibility for children and the home, especially for women. The high confidence intervals among men indicate the need for more research within the field with larger samples. PMID:26196280

Anxiety Disorders are Associated with Reduced Heart Rate Variability: A Meta-Analysis

PubMed Central

Chalmers, John A.; Quintana, Daniel S.; Abbott, Maree J.-Anne; Kemp, Andrew H.

2014-01-01

Background: Anxiety disorders increase risk of future cardiovascular disease (CVD) and mortality, even after controlling for confounds including smoking, lifestyle, and socioeconomic status, and irrespective of a history of medical disorders. While impaired vagal function, indicated by reductions in heart rate variability (HRV), may be one mechanism linking anxiety disorders to CVD, prior studies have reported inconsistent findings highlighting the need for meta-analysis. Method: Studies comparing resting-state HRV recordings in patients with an anxiety disorder as a primary diagnosis and healthy controls were considered for meta-analysis. Results: Meta-analyses were based on 36 articles, including 2086 patients with an anxiety disorder and 2294 controls. Overall, anxiety disorders were characterized by lower HRV [high frequency (HF): Hedges’ g = −0.29. 95% CI: −0.41 to −0.17, p < 0.001; time domain: Hedges’ g = −0.45, 95% CI: −0.57 to −0.33, p < 0.001] than controls. Panic disorder (n = 447), post-traumatic stress disorder (n = 192), generalized anxiety disorder (n = 68), and social anxiety disorder (n = 90), but not obsessive–compulsive disorder (n = 40), displayed reductions in HF HRV relative to controls (all ps < 0.001). Conclusion: Anxiety disorders are associated with reduced HRV, findings associated with a small-to-moderate effect size. Findings have important implications for future physical health and well-being of patients, highlighting a need for comprehensive cardiovascular risk reduction. PMID:25071612

Influence of management history and landscape variables on soil organic carbon and soil redistribution

USGS Publications Warehouse

Venteris, E.R.; McCarty, G.W.; Ritchie, J.C.; Gish, T.

2004-01-01

Controlled studies to investigate the interaction between crop growth, soil properties, hydrology, and management practices are common in agronomy. These sites (much as with real world farmland) often have complex management histories and topographic variability that must be considered. In 1993 an interdisiplinary study was started for a 20-ha site in Beltsville, MD. Soil cores (271) were collected in 1999 in a 30-m grid (with 5-m nesting) and analyzed as part of the site characterization. Soil organic carbon (SOC) and 137Cesium (137Cs) were measured. Analysis of aerial photography from 1992 and of farm management records revealed that part of the site had been maintained as a swine pasture and the other portion as cropped land. Soil properties, particularly soil redistribution and SOC, show large differences in mean values between the two areas. Mass C is 0.8 kg m -2 greater in the pasture area than in the cropped portion. The pasture area is primarily a deposition site, whereas the crop area is dominated by erosion. Management influence is suggested, but topographic variability confounds interpretation. Soil organic carbon is spatially structured, with a regionalized variable of 120 m. 137Cs activity lacks spatial structure, suggesting disturbance of the profile by animal activity and past structures such as swine shelters and roads. Neither SOC nor 137Cs were strongly correlated to terrain parameters, crop yields, or a seasonal soil moisture index predicted from crop yields. SOC and 137Cs were weakly correlated (r2 ???0.2, F-test P-value 0.001), suggesting that soil transport controls, in part, SOC distribution. The study illustrates the importance of past site history when interpreting the landscape distribution of soil properties, especially those strongly influenced by human activity. Confounding variables, complex soil hydrology, and incomplete documentation of land use history make definitive interpretations of the processes behind the spatial distributions difficult. Such complexity may limit the accuracy of scaling approaches to mapping SOC and soil redistribution.

Acute Alcohol Consumption, Alcohol Outlets, and Gun Suicide

PubMed Central

Branas, Charles C.; Richmond, Therese S.; Ten Have, Thomas R.; Wiebe, Douglas J.

2014-01-01

A case–control study of 149 intentionally self-inflicted gun injury cases (including completed gun suicides) and 302 population-based controls was conducted from 2003 to 2006 in a major US city. Two focal independent variables, acute alcohol consumption and alcohol outlet availability, were measured. Conditional logistic regression was adjusted for confounding variables. Gun suicide risk to individuals in areas of high alcohol outlet availability was less than the gun suicide risk they incurred from acute alcohol consumption, especially to excess. This corroborates prior work but also uncovers new information about the relationships between acute alcohol consumption, alcohol outlets, and gun suicide. Study limitations and implications are discussed. PMID:21929327

Acute alcohol consumption, alcohol outlets, and gun suicide.

PubMed

Branas, Charles C; Richmond, Therese S; Ten Have, Thomas R; Wiebe, Douglas J

2011-01-01

A case-control study of 149 intentionally self-inflicted gun injury cases (including completed gun suicides) and 302 population-based controls was conducted from 2003 to 2006 in a major US city. Two focal independent variables, acute alcohol consumption and alcohol outlet availability, were measured. Conditional logistic regression was adjusted for confounding variables. Gun suicide risk to individuals in areas of high alcohol outlet availability was less than the gun suicide risk they incurred from acute alcohol consumption, especially to excess. This corroborates prior work but also uncovers new information about the relationships between acute alcohol consumption, alcohol outlets, and gun suicide. Study limitations and implications are discussed.

Exploratory reconstructability analysis of accident TBI data

NASA Astrophysics Data System (ADS)

Zwick, Martin; Carney, Nancy; Nettleton, Rosemary

2018-02-01

This paper describes the use of reconstructability analysis to perform a secondary study of traumatic brain injury data from automobile accidents. Neutral searches were done and their results displayed with a hypergraph. Directed searches, using both variable-based and state-based models, were applied to predict performance on two cognitive tests and one neurological test. Very simple state-based models gave large uncertainty reductions for all three DVs and sizeable improvements in percent correct for the two cognitive test DVs which were equally sampled. Conditional probability distributions for these models are easily visualized with simple decision trees. Confounding variables and counter-intuitive findings are also reported.

Fish Oil Supplementation and Fatty Acid Synthase Expression in the Prostate: A Randomized Controlled Trial

DTIC Science & Technology

2010-03-20

olive oil (placebo) capsules (treatment 2). Potential confounding variables are assessed through completion of a comprehensive diet history...AD_________________ Award Number: W81XWH-04-1-0296 TITLE: Fish Oil Supplementation and Fatty Acid...FORM TO THE ABOVE ADDRESS. 31-03-2010 1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 0 3. DATES COVERED (From - To) Fish Oil Supplementation and

Equal Pay for Equal Work in Academic Obstetrics and Gynecology.

PubMed

Eichelberger, Kacey Y

2018-02-01

The most compelling data suggest women in academic obstetrics and gynecology earn approximately $36,000 less than male colleagues per year in regression models correcting for commonly cited explanatory variables. Although residual confounding may exist, academic departments in the United States should consider rigorous examination of their own internal metrics around salary to ensure gender-neutral compensation, commonly referred to as equal pay for equal work.

Nutritional status and the influence of TV consumption on female body size ideals in populations recently exposed to the media.

PubMed

Jucker, Jean-Luc; Thornborrow, Tracey; Beierholm, Ulrik; Burt, D Michael; Barton, Robert A; Evans, Elizabeth H; Jamieson, Mark A; Tovée, Martin J; Boothroyd, Lynda G

2017-08-16

Television consumption influences perceptions of attractive female body size. However, cross-cultural research examining media influence on body ideals is typically confounded by differences in the availability of reliable and diverse foodstuffs. 112 participants were recruited from 3 Nicaraguan villages that differed in television consumption and nutritional status, such that the contribution of both factors could be revealed. Participants completed a female figure preference task, reported their television consumption, and responded to several measures assessing nutritional status. Communities with higher television consumption and/or higher nutritional status preferred thinner female bodies than communities with lower television consumption and/or lower nutritional status. Bayesian mixed models estimated the plausible range of effects for television consumption, nutritional status, and other relevant variables on individual preferences. The model explained all meaningful differences between our low-nutrition villages, and television consumption, after sex, was the most likely of these predictors to contribute to variation in preferences (probability mass >95% when modelling only variables with zero-order associations with preferences, but only 90% when modelling all possible predictors). In contrast, we found no likely link with nutritional status. We thus found evidence that where media access and nutritional status are confounded, media is the more likely predictor of body ideals.

Errors in causal inference: an organizational schema for systematic error and random error.

PubMed

Suzuki, Etsuji; Tsuda, Toshihide; Mitsuhashi, Toshiharu; Mansournia, Mohammad Ali; Yamamoto, Eiji

2016-11-01

To provide an organizational schema for systematic error and random error in estimating causal measures, aimed at clarifying the concept of errors from the perspective of causal inference. We propose to divide systematic error into structural error and analytic error. With regard to random error, our schema shows its four major sources: nondeterministic counterfactuals, sampling variability, a mechanism that generates exposure events and measurement variability. Structural error is defined from the perspective of counterfactual reasoning and divided into nonexchangeability bias (which comprises confounding bias and selection bias) and measurement bias. Directed acyclic graphs are useful to illustrate this kind of error. Nonexchangeability bias implies a lack of "exchangeability" between the selected exposed and unexposed groups. A lack of exchangeability is not a primary concern of measurement bias, justifying its separation from confounding bias and selection bias. Many forms of analytic errors result from the small-sample properties of the estimator used and vanish asymptotically. Analytic error also results from wrong (misspecified) statistical models and inappropriate statistical methods. Our organizational schema is helpful for understanding the relationship between systematic error and random error from a previously less investigated aspect, enabling us to better understand the relationship between accuracy, validity, and precision. Copyright © 2016 Elsevier Inc. All rights reserved.

Association between indoor and outdoor air pollution and adolescent asthma from 1995 to 1996 in Taiwan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, T.N.; Ko, Y.C.; Chao, Y.Y.

The study aim was to estimate the contribution of indoor and outdoor air pollution to the 1-year prevalence of adolescent asthma after personal susceptibility and other potential risk factors were taken into account. A large-scaled cross-sectional study was conducted among 165,173 high school students aged 11 to 16 years in the different communities of Kaohsiung and Pintong in Taiwan, from October 1995 to June 1996. Each student and his/her parents participating in the study completed a video and a written International Study of Asthma and Allergies in Childhood questionnaire about symptoms of wheezing and allergies, passive smoking, and demographic variables.more » After adjustment for potential confounders, adolescents exposed to cigarette smoking and environmental tobacco smoke were found to suffer from asthma at an increased frequency. The authors observed a statistically significant association between outdoor air pollution and asthma, after controlling for potential confound variables. Total suspended particulate, nitrogen dioxide, carbon monoxide, ozone, and airborne dust particles all displayed an independent association with asthma, respectively. There were no selection biases in this community-based study, which provides evidence that passive smoking and long-term, high average outdoor air pollution are independent risk factors of asthma.« less

Quantification of the effects of ocean acidification on sediment microbial communities in the environment: the importance of ecosystem approaches.

PubMed

Hassenrück, Christiane; Fink, Artur; Lichtschlag, Anna; Tegetmeyer, Halina E; de Beer, Dirk; Ramette, Alban

2016-05-01

To understand how ocean acidification (OA) influences sediment microbial communities, naturally CO2-rich sites are increasingly being used as OA analogues. However, the characterization of these naturally CO2-rich sites is often limited to OA-related variables, neglecting additional environmental variables that may confound OA effects. Here, we used an extensive array of sediment and bottom water parameters to evaluate pH effects on sediment microbial communities at hydrothermal CO2 seeps in Papua New Guinea. The geochemical composition of the sediment pore water showed variations in the hydrothermal signature at seep sites with comparable pH, allowing the identification of sites that may better represent future OA scenarios. At these sites, we detected a 60% shift in the microbial community composition compared with reference sites, mostly related to increases in Chloroflexi sequences. pH was among the factors significantly, yet not mainly, explaining changes in microbial community composition. pH variation may therefore often not be the primary cause of microbial changes when sampling is done along complex environmental gradients. Thus, we recommend an ecosystem approach when assessing OA effects on sediment microbial communities under natural conditions. This will enable a more reliable quantification of OA effects via a reduction of potential confounding effects. © FEMS 2016.

Long-Term Coffee Consumption Is Associated with Decreased Incidence of New-Onset Hypertension: A Dose-Response Meta-Analysis.

PubMed

Grosso, Giuseppe; Micek, Agnieszka; Godos, Justyna; Pajak, Andrzej; Sciacca, Salvatore; Bes-Rastrollo, Maira; Galvano, Fabio; Martinez-Gonzalez, Miguel A

2017-08-17

To perform a dose-response meta-analysis of prospective cohort studies investigating the association between long-term coffee intake and risk of hypertension. An online systematic search of studies published up to November 2016 was performed. Linear and non-linear dose-response meta-analyses were conducted; potential evidence of heterogeneity, publication bias, and confounding effect of selected variables were investigated through sensitivity and meta-regression analyses. Seven cohorts including 205,349 individuals and 44,120 cases of hypertension were included. In the non-linear analysis, there was a 9% significant decreased risk of hypertension per seven cups of coffee a day, while, in the linear dose-response association, there was a 1% decreased risk of hypertension for each additional cup of coffee per day. Among subgroups, there were significant inverse associations for females, caffeinated coffee, and studies conducted in the US with longer follow-up. Analysis of potential confounders revealed that smoking-related variables weakened the strength of association between coffee consumption and risk of hypertension. Increased coffee consumption is associated with a modest decrease in risk of hypertension in prospective cohort studies. Smoking status is a potential effect modifier on the association between coffee consumption and risk of hypertension.

Goal specificity: a proxy measure for improvements in environmental outcomes in collaborative governance.

PubMed

Biddle, Jennifer C; Koontz, Tomas M

2014-12-01

Collaborative governance critics continually call for evidence to support its prevalent use. As is often the case in environmental policy, environmental outcomes occur at a rate incompatible with political agendas. In addition, a multitude of possibly confounding variables makes it difficult to correlate collaborative governance processes with environmental outcomes. The findings of this study offer empirical evidence that collaborative processes have a measurable, beneficial effect on environmental outcomes. Through the use of a unique paired-waterbody design, our dataset reduced the potential for confounding variables to impact our environmental outcome measurements. The results of a path analysis indicate that the output of setting specific pollutant reduction goals is significantly related to watershed partnerships' level of attainment of their environmental improvement goals. The action of setting specific goals (e.g. percentage of load reductions in pollutant levels) is fostered by sustained participation from partnership members throughout the lifecycle of the collaborative. In addition, this study demonstrates the utility of logic modeling for environmental planning and management, and suggests that the process of setting specific pollutant reduction goals is a useful proxy measure for reporting progress towards improvements in environmental outcomes when long-term environmental data are not available. Copyright © 2014 Elsevier Ltd. All rights reserved.

Measurement error is often neglected in medical literature: a systematic review.

PubMed

Brakenhoff, Timo B; Mitroiu, Marian; Keogh, Ruth H; Moons, Karel G M; Groenwold, Rolf H H; van Smeden, Maarten

2018-06-01

In medical research, covariates (e.g., exposure and confounder variables) are often measured with error. While it is well accepted that this introduces bias and imprecision in exposure-outcome relations, it is unclear to what extent such issues are currently considered in research practice. The objective was to study common practices regarding covariate measurement error via a systematic review of general medicine and epidemiology literature. Original research published in 2016 in 12 high impact journals was full-text searched for phrases relating to measurement error. Reporting of measurement error and methods to investigate or correct for it were quantified and characterized. Two hundred and forty-seven (44%) of the 565 original research publications reported on the presence of measurement error. 83% of these 247 did so with respect to the exposure and/or confounder variables. Only 18 publications (7% of 247) used methods to investigate or correct for measurement error. Consequently, it is difficult for readers to judge the robustness of presented results to the existence of measurement error in the majority of publications in high impact journals. Our systematic review highlights the need for increased awareness about the possible impact of covariate measurement error. Additionally, guidance on the use of measurement error correction methods is necessary. Copyright © 2018 Elsevier Inc. All rights reserved.

Viral Diseases in Zebrafish: What Is Known and Unknown

PubMed Central

Crim, Marcus J.; Riley, Lela K.

2013-01-01

Naturally occurring viral infections have the potential to introduce confounding variability that leads to invalid and misinterpreted data. Whereas the viral diseases of research rodents are well characterized and closely monitored, no naturally occurring viral infections have been characterized for the laboratory zebrafish (Danio rerio), an increasingly important biomedical research model. Despite the ignorance about naturally occurring zebrafish viruses, zebrafish models are rapidly expanding in areas of biomedical research where the confounding effects of unknown infectious agents present a serious concern. In addition, many zebrafish research colonies remain linked to the ornamental (pet) zebrafish trade, which can contribute to the introduction of new pathogens into research colonies, whereas mice used for research are purpose bred, with no introduction of new mice from the pet industry. Identification, characterization, and monitoring of naturally occurring viruses in zebrafish are crucial to the improvement of zebrafish health, the reduction of unwanted variability, and the continued development of the zebrafish as a model organism. This article addresses the importance of identifying and characterizing the viral diseases of zebrafish as the scope of zebrafish models expands into new research areas and also briefly addresses zebrafish susceptibility to experimental viral infection and the utility of the zebrafish as an infection and immunology model. PMID:23382345

Longitudinal associations of nutritional factors with glycated hemoglobin in youth with type 1 diabetes: the SEARCH Nutrition Ancillary Study123

PubMed Central

Crandell, Jamie L; Jaacks, Lindsay M; Couch, Sarah C; Lawrence, Jean M; Mayer-Davis, Elizabeth J

2015-01-01

Background: Improved glycated hemoglobin (Hb A1c) delays the progression of microvascular and macrovascular complications in individuals with type 1 diabetes (T1D). We previously showed that higher baseline intakes of n–3 (ω-3) fatty acids and leucine are associated with preserved β cell function 2 y later in youth with T1D. Objective: In the current study, we extend this work to explore the longitudinal associations of nutritional factors with Hb A1c in youth with T1D. Design: We included 908 T1D youth with baseline and follow-up Hb A1c measurements. Nutritional factors assessed at baseline were as follows: breastfeeding status and timing of complimentary food introduction; intakes of leucine, carbohydrates, protein, fat, and fiber estimated from a food-frequency questionnaire (FFQ); and plasma biomarkers for vitamins D and E, eicosapentaenoic acid (EPA), and docosahexaenoic acid. We fit linear regression models adjusted for baseline Hb A1c, sociodemographic variables, diabetes-related variables, time between baseline and follow-up visits, saturated fat, physical activity, and for FFQ-derived nutrients, total calories. The vitamin D model was further adjusted for season and body mass index z score. Results: The mean ± SD age and diabetes duration at baseline was 10.8 ± 3.9 y and 10.1 ± 5.8 mo, respectively. A total of 9.3% of participants had poor Hb A1c (value ≥9.5%) at baseline, which increased to 18.3% during follow-up (P < 0.0001). Intakes of EPA (β = −0.045, P = 0.046), leucine (β = −0.031, P = 0.0004), and protein (β = −0.003, P = 0.0002) were significantly negatively associated with follow-up Hb A1c after adjustment for confounders. Intake of carbohydrates was significantly positively (β = 0.001, P = 0.003) associated with follow-up Hb A1c after adjustment for confounders. Conclusions: Several nutritional factors may be associated with Hb A1c during early stages of disease progression in youth recently diagnosed with T1D. In addition to the overall role of major macronutrients such as carbohydrates and protein, leucine and n–3 fatty acid intakes, such as of EPA, may be important for long-term glycemic control. PMID:25948670

Maternal and neonatal individual risks and benefits associated with caesarean delivery: multicentre prospective study

PubMed Central

Carroli, Guillermo; Zavaleta, Nelly; Donner, Allan; Wojdyla, Daniel; Faundes, Anibal; Velazco, Alejandro; Bataglia, Vicente; Langer, Ana; Narváez, Alberto; Valladares, Eliette; Shah, Archana; Campodónico, Liana; Romero, Mariana; Reynoso, Sofia; de Pádua, Karla Simônia; Giordano, Daniel; Kublickas, Marius; Acosta, Arnaldo

2007-01-01

Objective To assess the risks and benefits associated with caesarean delivery compared with vaginal delivery. Design Prospective cohort study within the 2005 WHO global survey on maternal and perinatal health. Setting 410 health facilities in 24 areas in eight randomly selected Latin American countries; 123 were randomly selected and 120 participated and provided data Participants 106 546 deliveries reported during the three month study period, with data available for 97 095 (91% coverage). Main outcome measures Maternal, fetal, and neonatal morbidity and mortality associated with intrapartum or elective caesarean delivery, adjusted for clinical, demographic, pregnancy, and institutional characteristics. Results Women undergoing caesarean delivery had an increased risk of severe maternal morbidity compared with women undergoing vaginal delivery (odds ratio 2.0 (95% confidence interval 1.6 to 2.5) for intrapartum caesarean and 2.3 (1.7 to 3.1) for elective caesarean). The risk of antibiotic treatment after delivery for women having either type of caesarean was five times that of women having vaginal deliveries. With cephalic presentation, there was a trend towards a reduced odds ratio for fetal death with elective caesarean, after adjustment for possible confounding variables and gestational age (0.7, 0.4 to 1.0). With breech presentation, caesarean delivery had a large protective effect for fetal death. With cephalic presentation, however, independent of possible confounding variables and gestational age, intrapartum and elective caesarean increased the risk for a stay of seven or more days in neonatal intensive care (2.1 (1.8 to 2.6) and 1.9 (1.6 to 2.3), respectively) and the risk of neonatal mortality up to hospital discharge (1.7 (1.3 to 2.2) and 1.9 (1.5 to 2.6), respectively), which remained higher even after exclusion of all caesarean deliveries for fetal distress. Such increased risk was not seen for breech presentation. Lack of labour was a risk factor for a stay of seven or more days in neonatal intensive care and neonatal mortality up to hospital discharge for babies delivered by elective caesarean delivery, but rupturing of membranes may be protective. Conclusions Caesarean delivery independently reduces overall risk in breech presentations and risk of intrapartum fetal death in cephalic presentations but increases the risk of severe maternal and neonatal morbidity and mortality in cephalic presentations. PMID:17977819

Success Providing Postpartum Intrauterine Devices in Private-Sector Health Care Facilities in Nigeria: Factors Associated With Uptake

PubMed Central

Eluwa, George IE; Atamewalen, Ronke; Odogwu, Kingsley; Ahonsi, Babatunde

2016-01-01

ABSTRACT Background: Use of modern contraceptive methods in Nigeria remained at 10% between 2008 and 2013 despite substantive investments in family planning services. Many women in their first postpartum year, in particular, have an unmet need for family planning. We evaluated use of postpartum intrauterine device (IUD) insertion and determined factors associated with its uptake in Nigeria. Methods: Data were collected between May 2014 and February 2015 from 11 private health care facilities in 6 southern Nigerian states. Women attending antenatal care in participating facilities were counseled on all available contraceptive methods including the postpartum IUD. Data were abstracted from participating facility records and evaluated using a cross-sectional analysis. Categorical variables were calculated as proportions while continuous variables were calculated as medians with the associated interquartile range (IQR). Multivariate logistic regression analysis was used to identify factors associated with uptake of the postpartum IUD while controlling for potential confounding factors, including age, educational attainment, marital status, parity, number of living children, and previous use of contraception. Results: During the study period, 728 women delivered in the 11 facilities. The median age was 28 years, and most women were educated (73% had completed at least the secondary level). The majority (96%) of the women reported they were married, and the median number of living children was 3 (IQR, 2–4). Uptake of the postpartum IUD was 41% (n = 300), with 8% (n = 25) of the acceptors experiencing expulsion of the IUD within 6 weeks post-insertion. After controlling for potential confounding factors, several characteristics were associated with greater likelihood of choosing the postpartum IUD, including lower education, having a higher number of living children, and being single. Women who had used contraceptives previously were less likely to choose the postpartum IUD than women who had not previously used contraception (adjusted odds ratio, 0.68; 95% confidence interval, 0.55 to 0.84). Conclusion: A high percentage (41%) of women delivering in private health care facilities in southern Nigeria accepted immediate postpartum IUD insertion. Scale-up of postpartum IUD services is a promising approach to increasing uptake of long-acting reversible contraceptives among women in Nigeria. PMID:27353620

Structural Magnetic Resonance Imaging Correlates of Aggression in Psychosis: A Systematic Review and Effect Size Analysis.

PubMed

Widmayer, Sonja; Sowislo, Julia F; Jungfer, Hermann A; Borgwardt, Stefan; Lang, Undine E; Stieglitz, Rolf D; Huber, Christian G

2018-01-01

Background: Aggression in psychoses is of high clinical importance, and volumetric MRI techniques have been used to explore its structural brain correlates. Methods: We conducted a systematic review searching EMBASE, ScienceDirect, and PsycINFO through September 2017 using thesauri representing aggression, psychosis, and brain imaging. We calculated effect sizes for each study and mean Hedge's g for whole brain (WB) volume. Methodological quality was established using the PRISMA checklist (PROSPERO: CRD42014014461). Results: Our sample consisted of 12 studies with 470 patients and 155 healthy controls (HC). After subtracting subjects due to cohort overlaps, 314 patients and 96 HC remained. Qualitative analyses showed lower volumes of WB, prefrontal regions, temporal lobe, hippocampus, thalamus and cerebellum, and higher volumes of lateral ventricles, amygdala, and putamen in violent vs. non-violent people with schizophrenia. In quantitative analyses, violent persons with schizophrenia exhibited a significantly lower WB volume than HC ( p = 0.004), and also lower than non-violent persons with schizophrenia ( p = 0.007). Conclusions: We reviewed evidence for differences in brain volume correlates of aggression in persons with schizophrenia. Our results point toward a reduced whole brain volume in violent as opposed to non-violent persons with schizophrenia. However, considerable sample overlap in the literature, lack of reporting of potential confounding variables, and missing research on affective psychoses limit our explanatory power. To permit stronger conclusions, further studies evaluating structural correlates of aggression in psychotic disorders are needed.

Three estimates of the association between linear growth failure and cognitive ability.

PubMed

Cheung, Y B; Lam, K F

2009-09-01

To compare three estimators of association between growth stunting as measured by height-for-age Z-score and cognitive ability in children, and to examine the extent statistical adjustment for covariates is useful for removing confounding due to socio-economic status. Three estimators, namely random-effects, within- and between-cluster estimators, for panel data were used to estimate the association in a survey of 1105 pairs of siblings who were assessed for anthropometry and cognition. Furthermore, a 'combined' model was formulated to simultaneously provide the within- and between-cluster estimates. Random-effects and between-cluster estimators showed strong association between linear growth and cognitive ability, even after adjustment for a range of socio-economic variables. In contrast, the within-cluster estimator showed a much more modest association: For every increase of one Z-score in linear growth, cognitive ability increased by about 0.08 standard deviation (P < 0.001). The combined model verified that the between-cluster estimate was significantly larger than the within-cluster estimate (P = 0.004). Residual confounding by socio-economic situations may explain a substantial proportion of the observed association between linear growth and cognition in studies that attempt to control the confounding by means of multivariable regression analysis. The within-cluster estimator provides more convincing and modest results about the strength of association.

Bias with respect to socioeconomic status: A closer look at zip code matching in a pneumococcal vaccine effectiveness study.

PubMed

Link-Gelles, Ruth; Westreich, Daniel; Aiello, Allison E; Shang, Nong; Weber, David J; Holtzman, Corinne; Scherzinger, Karen; Reingold, Arthur; Schaffner, William; Harrison, Lee H; Rosen, Jennifer B; Petit, Susan; Farley, Monica; Thomas, Ann; Eason, Jeffrey; Wigen, Christine; Barnes, Meghan; Thomas, Ola; Zansky, Shelley; Beall, Bernard; Whitney, Cynthia G; Moore, Matthew R

2016-12-01

In 2010, 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the US for prevention of invasive pneumococcal disease in children. Individual-level socioeconomic status (SES) is a potential confounder of the estimated effectiveness of PCV13 and is often controlled for in observational studies using zip code as a proxy. We assessed the utility of zip code matching for control of SES in a post-licensure evaluation of the effectiveness of PCV13 (calculated as [1-matched odds ratio]*100). We used a directed acyclic graph to identify subsets of confounders and collected SES variables from birth certificates, geo-coding, a parent interview, and follow-up with medical providers. Cases tended to be more affluent than eligible controls (for example, 48.3% of cases had private insurance vs. 44.6% of eligible controls), but less affluent than enrolled controls (52.9% of whom had private insurance). Control of confounding subsets, however, did not result in a meaningful change in estimated vaccine effectiveness (original estimate: 85.1%, 95% CI 74.8-91.9%; adjusted estimate: 82.5%, 95% CI 65.6-91.1%). In the context of a post-licensure vaccine effectiveness study, zip code appears to be an adequate, though not perfect, proxy for individual SES.

Work-Home Interference, Perceived Total Workload, and the Risk of Future Sickness Absence Due to Stress-Related Mental Diagnoses Among Women and Men: a Prospective Twin Study.

PubMed

Svedberg, Pia; Mather, Lisa; Bergström, Gunnar; Lindfors, Petra; Blom, Victoria

2018-02-01

Work-home interference has been proposed as an important explanation for sickness absence (SA). Previous studies show mixed results, have not accounted for familial factors (genetics and shared everyday environment), or investigated diagnosis specific SA. The aim was to study whether work-home interference and perceived total workload predict SA due to stress-related mental diagnoses, or SA due to other mental diagnoses, among women and men, when adjusting for various confounders and familial factors. This study included 11,916 twins, 19-47 years (49% women). Data on work-to-home and home-to-work conflicts, perceived total workload, and relevant confounders were derived from a 2005 survey, and national register data on SA spells until 2013 were obtained. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Discordant twin pair design was applied to adjust for familial factors. Each one unit increase in work-to-home and home-to-work conflicts, and perceived total workload was associated with higher odds for SA due to stress-related mental diagnoses and to SA due to other mental diagnoses among women, when adjusting for sociodemographic factors (ORs 1.15-1.31). Including health or familial factors, no associations remained. For men, each one unit increase in work-to-home conflicts was associated with higher odds for SA due to stress-related diagnoses (ORs 1.23-1.35), independently of confounders. Work-to-home conflict was independently associated with future SA due to stress-related diagnoses among men only. Health- and work-related factors seem to be important confounders when researching work-home interference, perceived total workload, and SA. Not including such confounders involves risking drawing incorrect conclusions. Further studies are needed to confirm sex differences and whether genetic factors are important for the associations studied.

What are the causal effects of breastfeeding on IQ, obesity and blood pressure? Evidence from comparing high-income with middle-income cohorts.

PubMed

Brion, Marie-Jo A; Lawlor, Debbie A; Matijasevich, Alicia; Horta, Bernardo; Anselmi, Luciana; Araújo, Cora L; Menezes, Ana Maria B; Victora, Cesar G; Smith, George Davey

2011-06-01

A novel approach is explored for improving causal inference in observational studies by comparing cohorts from high-income with low- or middle-income countries (LMIC), where confounding structures differ. This is applied to assessing causal effects of breastfeeding on child blood pressure (BP), body mass index (BMI) and intelligence quotient (IQ). Standardized approaches for assessing the confounding structure of breastfeeding by socio-economic position were applied to the British Avon Longitudinal Study of Parents and Children (ALSPAC) (N ≃ 5000) and Brazilian Pelotas 1993 cohorts (N ≃ 1000). This was used to improve causal inference regarding associations of breastfeeding with child BP, BMI and IQ. Analyses were extended to include results from a meta-analysis of five LMICs (N ≃ 10 000) and compared with a randomized trial of breastfeeding promotion. Findings Although higher socio-economic position was strongly associated with breastfeeding in ALSPAC, there was little such patterning in Pelotas. In ALSPAC, breastfeeding was associated with lower BP, lower BMI and higher IQ, adjusted for confounders, but in the directions expected if due to socioeconomic patterning. In contrast, in Pelotas, breastfeeding was not strongly associated with BP or BMI but was associated with higher IQ. Differences in associations observed between ALSPAC and the LMIC meta-analysis were in line with those observed between ALSPAC and Pelotas, but with robust evidence of heterogeneity detected between ALSPAC and the LMIC meta-analysis associations. Trial data supported the conclusions inferred by the cross-cohort comparisons, which provided evidence for causal effects on IQ but not for BP or BMI. While reported associations of breastfeeding with child BP and BMI are likely to reflect residual confounding, breastfeeding may have causal effects on IQ. Comparing associations between populations with differing confounding structures can be used to improve causal inference in observational studies.

Standing beat-to-beat blood pressure variability is reduced among fallers in the Malaysian Elders Longitudinal Study.

PubMed

Goh, Choon-Hian; Ng, Siew-Cheok; Kamaruzzaman, Shahrul Bahyah; Chin, Ai-Vyrn; Tan, Maw Pin

2017-10-01

The aim of this study was to determine the relationship between falls and beat-to-beat blood pressure (BP) variability.Continuous noninvasive BP measurement is as accurate as invasive techniques. We evaluated beat-to-beat supine and standing BP variability (BPV) using time and frequency domain analysis from noninvasive continuous BP recordings.A total of 1218 older adults were selected. Continuous BP recordings obtained were analyzed to determine standard deviation (SD) and root mean square of real variability (RMSRV) for time domain BPV and fast-Fourier transform low frequency (LF), high frequency (HF), total power spectral density (PSD), and LF:HF ratio for frequency domain BPV.Comparisons were performed between 256 (21%) individuals with at least 1 fall in the past 12 months and nonfallers. Fallers were significantly older (P = .007), more likely to be female (P = .006), and required a longer time to complete the Timed-Up and Go test (TUG) and frailty walk test (P ≤ .001). Standing systolic BPV (SBPV) was significantly lower in fallers compared to nonfallers (SBPV-SD, P = .016; SBPV-RMSRV, P = .033; SBPV-LF, P = .003; SBPV-total PSD, P = .012). Nonfallers had significantly higher supine to standing ratio (SSR) for SBPV-SD, SBPV-RMSRV, and SBPV-total PSD (P = .017, P = .013, and P = .009). In multivariate analyses, standing BPV remained significantly lower in fallers compared to nonfallers after adjustment for age, sex, diabetes, frailty walk, and supine systolic BP. The reduction in frequency-domain SSR among fallers was attenuated by supine systolic BP, TUG, and frailty walk.In conclusion, reduced beat-to-beat BPV while standing is independently associated with increased risk of falls. Changes between supine and standing BPV are confounded by supine BP and walking speed.

Relation of Heart Rate and its Variability during Sleep with Age, Physical Activity, and Body Composition in Young Children

PubMed Central

Herzig, David; Eser, Prisca; Radtke, Thomas; Wenger, Alina; Rusterholz, Thomas; Wilhelm, Matthias; Achermann, Peter; Arhab, Amar; Jenni, Oskar G.; Kakebeeke, Tanja H.; Leeger-Aschmann, Claudia S.; Messerli-Bürgy, Nadine; Meyer, Andrea H.; Munsch, Simone; Puder, Jardena J.; Schmutz, Einat A.; Stülb, Kerstin; Zysset, Annina E.; Kriemler, Susi

2017-01-01

Background: Recent studies have claimed a positive effect of physical activity and body composition on vagal tone. In pediatric populations, there is a pronounced decrease in heart rate with age. While this decrease is often interpreted as an age-related increase in vagal tone, there is some evidence that it may be related to a decrease in intrinsic heart rate. This factor has not been taken into account in most previous studies. The aim of the present study was to assess the association between physical activity and/or body composition and heart rate variability (HRV) independently of the decline in heart rate in young children. Methods: Anthropometric measurements were taken in 309 children aged 2–6 years. Ambulatory electrocardiograms were collected over 14–18 h comprising a full night and accelerometry over 7 days. HRV was determined of three different night segments: (1) over 5 min during deep sleep identified automatically based on HRV characteristics; (2) during a 20 min segment starting 15 min after sleep onset; (3) over a 4-h segment between midnight and 4 a.m. Linear models were computed for HRV parameters with anthropometric and physical activity variables adjusted for heart rate and other confounding variables (e.g., age for physical activity models). Results: We found a decline in heart rate with increasing physical activity and decreasing skinfold thickness. HRV parameters decreased with increasing age, height, and weight in HR-adjusted regression models. These relationships were only found in segments of deep sleep detected automatically based on HRV or manually 15 min after sleep onset, but not in the 4-h segment with random sleep phases. Conclusions: Contrary to most previous studies, we found no increase of standard HRV parameters with age, however, when adjusted for heart rate, there was a significant decrease of HRV parameters with increasing age. Without knowing intrinsic heart rate correct interpretation of HRV in growing children is impossible. PMID:28286485

Relation of Heart Rate and its Variability during Sleep with Age, Physical Activity, and Body Composition in Young Children.

PubMed

Herzig, David; Eser, Prisca; Radtke, Thomas; Wenger, Alina; Rusterholz, Thomas; Wilhelm, Matthias; Achermann, Peter; Arhab, Amar; Jenni, Oskar G; Kakebeeke, Tanja H; Leeger-Aschmann, Claudia S; Messerli-Bürgy, Nadine; Meyer, Andrea H; Munsch, Simone; Puder, Jardena J; Schmutz, Einat A; Stülb, Kerstin; Zysset, Annina E; Kriemler, Susi

2017-01-01

Background: Recent studies have claimed a positive effect of physical activity and body composition on vagal tone. In pediatric populations, there is a pronounced decrease in heart rate with age. While this decrease is often interpreted as an age-related increase in vagal tone, there is some evidence that it may be related to a decrease in intrinsic heart rate. This factor has not been taken into account in most previous studies. The aim of the present study was to assess the association between physical activity and/or body composition and heart rate variability (HRV) independently of the decline in heart rate in young children. Methods: Anthropometric measurements were taken in 309 children aged 2-6 years. Ambulatory electrocardiograms were collected over 14-18 h comprising a full night and accelerometry over 7 days. HRV was determined of three different night segments: (1) over 5 min during deep sleep identified automatically based on HRV characteristics; (2) during a 20 min segment starting 15 min after sleep onset; (3) over a 4-h segment between midnight and 4 a.m. Linear models were computed for HRV parameters with anthropometric and physical activity variables adjusted for heart rate and other confounding variables (e.g., age for physical activity models). Results: We found a decline in heart rate with increasing physical activity and decreasing skinfold thickness. HRV parameters decreased with increasing age, height, and weight in HR-adjusted regression models. These relationships were only found in segments of deep sleep detected automatically based on HRV or manually 15 min after sleep onset, but not in the 4-h segment with random sleep phases. Conclusions: Contrary to most previous studies, we found no increase of standard HRV parameters with age, however, when adjusted for heart rate, there was a significant decrease of HRV parameters with increasing age. Without knowing intrinsic heart rate correct interpretation of HRV in growing children is impossible.

Dietary Fiber Is Positively Associated with Cognitive Control among Prepubertal Children12

PubMed Central

Khan, Naiman A; Raine, Lauren B; Drollette, Eric S; Scudder, Mark R; Kramer, Arthur F; Hillman, Charles H

2015-01-01

Background: Converging evidence now indicates that aerobic fitness and adiposity are key correlates of childhood cognitive function and brain health. However, the evidence relating dietary intake to executive function/cognitive control remains limited. Objective: The current study assessed cross-sectional associations between performance on an attentional inhibition task and dietary fatty acids (FAs), fiber, and overall diet quality among children aged 7–9 y (n = 65). Methods: Attentional inhibition was assessed by using a modified flanker task. Three-day food records were used to conduct nutrient-level analyses and to calculate diet quality (Healthy Eating Index–2005) scores. Results: Bivariate correlations revealed that socioeconomic status and sex were not related to task performance or diet measures. However, age, intelligence quotient (IQ), pubertal staging, maximal oxygen uptake (V̇O2max), and percentage of fat mass (%fat mass) correlated with task accuracy. Hierarchical regression models were used to determine the relation between diet variables and task accuracy and reaction time across both congruent and incongruent trials of the flanker task. After adjustment of confounding variables (age, IQ, pubertal staging, V̇O2max, and %fat mass), congruent accuracy was positively associated with insoluble fiber (β = 0.26, P = 0.03) and total dietary fiber (β = 0.23, P = 0.05). Incongruent response accuracy was positively associated with insoluble fiber (β = 0.35, P < 0.01), pectins (β = 0.25, P = 0.04), and total dietary fiber (β = 0.32, P < 0.01). Higher diet quality was related to lower accuracy interference (β = −0.26, P = 0.03), whereas higher total FA intake was related to greater accuracy interference (β = 0.24, P = 0.04). No statistically significant associations were observed between diet variables and reaction time measures. Conclusion: These results demonstrate that children’s diet quality, specifically dietary fiber, is an important correlate of performance on a cognitive task requiring variable amounts of cognitive control. PMID:25527669

Robust MR-based approaches to quantifying white matter structure and structure/function alterations in Huntington's disease

PubMed Central

Steventon, Jessica J.; Trueman, Rebecca C.; Rosser, Anne E.; Jones, Derek K.

2016-01-01

Background Huge advances have been made in understanding and addressing confounds in diffusion MRI data to quantify white matter microstructure. However, there has been a lag in applying these advances in clinical research. Some confounds are more pronounced in HD which impedes data quality and interpretability of patient-control differences. This study presents an optimised analysis pipeline and addresses specific confounds in a HD patient cohort. Method 15 HD gene-positive and 13 matched control participants were scanned on a 3T MRI system with two diffusion MRI sequences. An optimised post processing pipeline included motion, eddy current and EPI correction, rotation of the B matrix, free water elimination (FWE) and tractography analysis using an algorithm capable of reconstructing crossing fibres. The corpus callosum was examined using both a region-of-interest and a deterministic tractography approach, using both conventional diffusion tensor imaging (DTI)-based and spherical deconvolution analyses. Results Correcting for CSF contamination significantly altered microstructural metrics and the detection of group differences. Reconstructing the corpus callosum using spherical deconvolution produced a more complete reconstruction with greater sensitivity to group differences, compared to DTI-based tractography. Tissue volume fraction (TVF) was reduced in HD participants and was more sensitive to disease burden compared to DTI metrics. Conclusion Addressing confounds in diffusion MR data results in more valid, anatomically faithful white matter tract reconstructions with reduced within-group variance. TVF is recommended as a complementary metric, providing insight into the relationship with clinical symptoms in HD not fully captured by conventional DTI metrics. PMID:26335798

Is the association between posttraumatic stress disorder symptoms and poor health due to a common familial or genetic factor?

PubMed Central

Roy-Byrne, Peter P.; Noonan, Carolyn; Afari, Niloofar; Buchwald, Dedra; Goldberg, Jack

2010-01-01

Objective The objective of this study was to identify genetic, familial and environmental contributions to the association between posttraumatic stress disorder (PTSD) symptoms and poor health. Methods A community sample of 1852 twin pairs was assessed for symptoms of PTSD [with the Impact of Events Scale (IES)] and self-reported global health status using a single five-level question. An ordinal logistic regression model estimated odds ratio/s (OR) for the association between PTSD and health status. Within-pair analysis assessed confounding by familial and genetic factors and adjusted for the possible confounding influence of age, sex, race, education and self-reported physician diagnosis of depression. Results The IES was strongly and significantly associated with self-reported health [OR = 1.8; 95% confidence interval (95% CI) = 1.5–2.2; highest quartile vs. lowest quartile]. This association remained significant in within-pair analysis (OR = 1.3; 95% CI=1.0–1.7), but after further adjustment for sociodemographics and depression, it was no longer significant (Ptrend=.17). Separate analysis by zygosity did not show differential effect in monozygotic or dizygotic pairs. Conclusion These findings suggest that the association between PTSD symptoms and poor health is, in part, due to familial confounding and sociodemographic factors. Little evidence of confounding by genetic factors was found. These findings suggest that early prevention efforts would have the greatest potential for improving poor health in PTSD-prone patients, whereas later intervention efforts directed at treating PTSD may have a more limited impact on improving poor health. PMID:16950376

Appendicular and whole body lean mass outcomes are associated with finite element analysis-derived bone strength at the distal radius and tibia in adults aged 40years and older.

PubMed

Gibbs, Jenna C; Giangregorio, Lora M; Wong, Andy K O; Josse, Robert G; Cheung, Angela M

2017-10-01

The purpose of this cross-sectional study was to determine how appendicular lean mass index (ALMI), and whole body lean (LMI) and fat mass indices (FMI) associate with estimated bone strength outcomes at the distal radius and tibia in adults aged 40 years and older. Dual energy X-ray absorptiometry (DXA) scans were performed to determine body composition, including whole body lean and fat mass, and appendicular lean mass. ALMI (appendicular lean mass/height 2 ), LMI (lean tissue mass/height 2 ) and FMI (fat mass/height 2 ) were calculated. High-resolution peripheral quantitative computed tomography (HRpQCT) scans were performed to assess bone structural properties at the distal radius and tibia. Using finite element analysis, failure load (N), stiffness (N/mm), ultimate stress (MPa), and cortical-to-trabecular load ratio were estimated from HRpQCT scans. The associations between body composition (ALMI, LMI, FMI) and estimated bone strength were examined using bivariate and multivariable linear regression analyses adjusting for age, sex, and other confounding variables. In 197 participants (127 women; mean±SD, age: 69.5±10.3y, body mass index: 27.95±4.95kg/m 2 , ALMI: 7.31±1.31kg/m 2 ), ALMI and LMI were significantly associated with failure load at the distal radius and tibia (explained 39%-48% of the variance) and remained significant after adjusting for confounding variables and multiple testing (R 2 =0.586-0.645, p<0.001). ALMI, LMI, and FMI did not have significant associations with ultimate stress in our multivariable models. FMI was significantly associated with cortical-to-trabecular load ratio at the distal radius and tibia (explained 6%-12% of the variance) and remained significant after adjusting for confounders and multiple testing (R 2 =0.208-0.243, p<0.001). FMI was no longer significantly associated with failure load after adjusting for confounders. These findings suggest that ALMI and LMI are important determinants of estimated bone strength, particularly failure load, at the distal radius and tibia, and may contribute to preservation of bone strength in middle-to-late adulthood. Copyright © 2017 Elsevier Inc. All rights reserved.

Partial Granger causality--eliminating exogenous inputs and latent variables.

PubMed

Guo, Shuixia; Seth, Anil K; Kendrick, Keith M; Zhou, Cong; Feng, Jianfeng

2008-07-15

Attempts to identify causal interactions in multivariable biological time series (e.g., gene data, protein data, physiological data) can be undermined by the confounding influence of environmental (exogenous) inputs. Compounding this problem, we are commonly only able to record a subset of all related variables in a system. These recorded variables are likely to be influenced by unrecorded (latent) variables. To address this problem, we introduce a novel variant of a widely used statistical measure of causality--Granger causality--that is inspired by the definition of partial correlation. Our 'partial Granger causality' measure is extensively tested with toy models, both linear and nonlinear, and is applied to experimental data: in vivo multielectrode array (MEA) local field potentials (LFPs) recorded from the inferotemporal cortex of sheep. Our results demonstrate that partial Granger causality can reveal the underlying interactions among elements in a network in the presence of exogenous inputs and latent variables in many cases where the existing conditional Granger causality fails.

A genetically informed study of the association between harsh punishment and offspring behavioral problems.

PubMed

Lynch, Stacy K; Turkheimer, Eric; D'Onofrio, Brian M; Mendle, Jane; Emery, Robert E; Slutske, Wendy S; Martin, Nicholas G

2006-06-01

Conclusions about the effects of harsh parenting on children have been limited by research designs that cannot control for genetic or shared environmental confounds. The present study used a sample of children of twins and a hierarchical linear modeling statistical approach to analyze the consequences of varying levels of punishment while controlling for many confounding influences. The sample of 887 twin pairs and 2,554 children came from the Australian Twin Registry. Although corporal punishment per se did not have significant associations with negative childhood outcomes, harsher forms of physical punishment did appear to have specific and significant effects. The observed association between harsh physical punishment and negative outcomes in children survived a relatively rigorous test of its causal status, thereby increasing the authors' conviction that harsh physical punishment is a serious risk factor for children. ((c) 2006 APA, all rights reserved).

A Genetically Informed Study of the Association Between Harsh Punishment and Offspring Behavioral Problems

PubMed Central

Lynch, Stacy K.; Turkheimer, Eric; D’Onofrio, Brian M.; Mendle, Jane; Emery, Robert E.; Slutske, Wendy S.; Martin, Nicholas G.

2010-01-01

Conclusions about the effects of harsh parenting on children have been limited by research designs that cannot control for genetic or shared environmental confounds. The present study used a sample of children of twins and a hierarchical linear modeling statistical approach to analyze the consequences of varying levels of punishment while controlling for many confounding influences. The sample of 887 twin pairs and 2,554 children came from the Australian Twin Registry. Although corporal punishment per se did not have significant associations with negative childhood outcomes, harsher forms of physical punishment did appear to have specific and significant effects. The observed association between harsh physical punishment and negative outcomes in children survived a relatively rigorous test of its causal status, thereby increasing the authors’ conviction that harsh physical punishment is a serious risk factor for children. PMID:16756394

Prevalence of traumatic brain injury in intimate partner violence offenders compared to the general population: a meta-analysis.

PubMed

Farrer, Thomas J; Frost, R Brock; Hedges, Dawson W

2012-04-01

Intimate partner violence (IPV) is widespread. Several risk factors are associated with IPV perpetuation, including alcohol use and educational level. The aggression and violence associated with traumatic brain injury (TBI) suggest that brain trauma may also be a risk factor for IPV. To examine the association between TBI and IPV, the authors conducted a meta-analysis of peer-reviewed published studies reporting the prevalence of TBI in IPV perpetrators. The authors compared the frequency of TBI among IPV perpetuators to estimates of TBI in the general population using a single-sample test of proportions. Six studies containing a total of 222 subjects met inclusion criteria. Fifty-three percent (119) of the IPV perpetuators had a history of TBI, a prevalence significantly higher (p < .0001) than estimates of TBI in the general population. The prevalence of TBI among perpetuators of IPV appears significantly higher than the prevalence of TBI in the general population. To the extent that this association is causal, TBI may be a risk factor for interpersonal violence, although comparatively few source studies, lack of standardized information about TBI severity, and the inability to investigate potential confounding variables necessarily limit this conclusion.

Hepatotoxicity and subchronic toxicity tests of Morinda citrifolia (noni) fruit.

PubMed

West, Brett J; Su, Chen X; Jensen, C Jarakae

2009-10-01

Morinda citrifolia (noni) fruit juice has been approved as a safe food in many nations. A few cases of hepatitis in people who had been drinking noni juice have been reported, even though no causal link could be established between the liver injury and ingestion of the juice. To more fully evaluate the hepatotoxic potential of noni fruit juice, in vitro hepatotoxicity tests were conducted in human liver cells, HepG2 cell line. A subchronic oral toxicity test of noni fruit was also performed in Sprague-Dawley (SD) rats to provide benchmark data for understanding the safety of noni juice, without the potential confounding variables associated with many commercial noni juice products. Freeze-dried filtered noni fruit puree did not decrease HepG2 cell viability or induce neutral lipid accumulation and phospholipidosis. There were no histopathological changes or evidence of dose-responses in hematological and clinical chemistry measurements, including liver function tests. The no-observed-adverse-effect level (NOAEL) for freeze-dried noni fruit puree is greater than 6.86 g/kg body weight, equivalent to approximately 90 ml of noni fruit juice/kg. These findings corroborate previous conclusions that consumption of noni fruit juice is unlikely to induce adverse liver effects.

Associations Between Socioeconomic Status and Allostatic Load: Effects of Neighborhood Poverty and Tests of Mediating Pathways

PubMed Central

Mentz, Graciela; Lachance, Laurie; Johnson, Jonetta; Gaines, Causandra; Israel, Barbara A.

2012-01-01

Objectives. We examined relationships between neighborhood poverty and allostatic load in a low- to moderate-income multiracial urban community. We tested the hypothesis that neighborhood poverty is associated with allostatic load, controlling for household poverty. We also examined the hypotheses that this association was mediated by psychosocial stress and health-related behaviors. Methods. We conducted multilevel analyses using cross-sectional data from a probability sample survey in Detroit, Michigan (n = 919) and the 2000 US Census. The outcome measure was allostatic load. Independent variables included neighborhood and household poverty, psychosocial stress, and health-related behaviors. Covariates included neighborhood and individual demographic characteristics. Results. Neighborhood poverty was positively associated with allostatic load (P < .05), independent of household poverty and controlling for potential confounders. Relationships between neighborhood poverty were mediated by self-reported neighborhood environment stress but not by health-related behaviors. Conclusions. Neighborhood poverty is associated with wear and tear on physiological systems, and this relationship is mediated through psychosocial stress. These relationships are evident after accounting for household poverty levels. Efforts to promote health equity should focus on neighborhood poverty, associated stressful environmental conditions, and household poverty. PMID:22873478

Portion Size: What We Know and What We Need to Know

PubMed Central

Benton, David

2015-01-01

There is increasing evidence that the portion sizes of many foods have increased and in a laboratory at least this increases the amount eaten. The conclusions are, however, limited by the complexity of the phenomenon. There is a need to consider meals freely chosen over a prolonged period when a range of foods of different energy densities are available. A range of factors will influence the size of the portion size chosen: amongst others packaging, labeling, advertising, and the unit size rather than portion size of the food item. The way portion size interacts with the multitude of factors that determine food intake needs to be established. In particular, the role of portion size on energy intake should be examined as many confounding variables exist and we must be clear that it is portion size that is the major problem. If the approach is to make a practical contribution, then methods of changing portion sizes will need to be developed. This may prove to be a problem in a free market, as it is to be expected that customers will resist the introduction of smaller portion sizes, given that value for money is an important motivator. PMID:24915353