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Sample records for 3pl irt model

  1. Some Observations on the Identification and Interpretation of the 3PL IRT Model

    ERIC Educational Resources Information Center

    Azevedo, Caio Lucidius Naberezny

    2009-01-01

    The paper by Maris, G., & Bechger, T. (2009) entitled, "On the Interpreting the Model Parameters for the Three Parameter Logistic Model," addressed two important questions concerning the three parameter logistic (3PL) item response theory (IRT) model (and in a broader sense, concerning all IRT models). The first one is related to the model…

  2. Alternative Matching Scores to Control Type I Error of the Mantel-Haenszel Procedure for DIF in Dichotomously Scored Items Conforming to 3PL IRT and Nonparametric 4PBCB Models

    ERIC Educational Resources Information Center

    Monahan, Patrick O.; Ankenmann, Robert D.

    2010-01-01

    When the matching score is either less than perfectly reliable or not a sufficient statistic for determining latent proficiency in data conforming to item response theory (IRT) models, Type I error (TIE) inflation may occur for the Mantel-Haenszel (MH) procedure or any differential item functioning (DIF) procedure that matches on summed-item…

  3. Standard Error Estimation of 3PL IRT True Score Equating with an MCMC Method

    ERIC Educational Resources Information Center

    Liu, Yuming; Schulz, E. Matthew; Yu, Lei

    2008-01-01

    A Markov chain Monte Carlo (MCMC) method and a bootstrap method were compared in the estimation of standard errors of item response theory (IRT) true score equating. Three test form relationships were examined: parallel, tau-equivalent, and congeneric. Data were simulated based on Reading Comprehension and Vocabulary tests of the Iowa Tests of…

  4. 3PL: A Useful Model with a Mild Estimation Problem

    ERIC Educational Resources Information Center

    Partchev, Ivailo

    2009-01-01

    This author has always felt a bit uneasy about the three parameter logistic (3PL) model because it seems about as prone to discovering guessing when guessing does not take place, as the Rasch model is reluctant to admit that guessing might ever take place at all. However, the author has attributed this to the prior "magic" employed when estimating…

  5. The Exploration of the Relationship between Guessing and Latent Ability in IRT Models

    ERIC Educational Resources Information Center

    Gao, Song

    2011-01-01

    This study explored the relationship between successful guessing and latent ability in IRT models. A new IRT model was developed with a guessing function integrating probability of guessing an item correctly with the examinee's ability and the item parameters. The conventional 3PL IRT model was compared with the new 2PL-Guessing model on…

  6. Applications of Multilevel IRT Modeling

    ERIC Educational Resources Information Center

    Fox, Jean-Paul

    2004-01-01

    The recent development of multilevel IRT models (Fox & Glas, 2001, 2003) has been shown to be very useful for analyzing relationships between observed variables on different levels containing measurement error. Model parameter estimates and their standard deviations are concurrently estimated taking account of measurement error in observed…

  7. A Paradox between IRT Invariance and Model-Data Fit When Utilizing the One-Parameter and Three-Parameter Models

    ERIC Educational Resources Information Center

    Custer, Michael; Sharairi, Sid; Yamazaki, Kenji; Signatur, Diane; Swift, David; Frey, Sharon

    2008-01-01

    The present study compared item and ability invariance as well as model-data fit between the one-parameter (1PL) and three-parameter (3PL) Item Response Theory (IRT) models utilizing real data across five grades; second through sixth as well as simulated data at second, fourth and sixth grade. At each grade, the 1PL and 3PL IRT models were run…

  8. Embedding IRT in Structural Equation Models: A Comparison with Regression Based on IRT Scores

    ERIC Educational Resources Information Center

    Lu, Irene R. R.; Thomas, D. Roland; Zumbo, Bruno D.

    2005-01-01

    This article reviews the problems associated with using item response theory (IRT)-based latent variable scores for analytical modeling, discusses the connection between IRT and structural equation modeling (SEM)-based latent regression modeling for discrete data, and compares regression parameter estimates obtained using predicted IRT scores and…

  9. Variance Decomposition Using an IRT Measurement Model

    PubMed Central

    Glas, Cees A. W.; Boomsma, Dorret I.

    2007-01-01

    Large scale research projects in behaviour genetics and genetic epidemiology are often based on questionnaire or interview data. Typically, a number of items is presented to a number of subjects, the subjects’ sum scores on the items are computed, and the variance of sum scores is decomposed into a number of variance components. This paper discusses several disadvantages of the approach of analysing sum scores, such as the attenuation of correlations amongst sum scores due to their unreliability. It is shown that the framework of Item Response Theory (IRT) offers a solution to most of these problems. We argue that an IRT approach in combination with Markov chain Monte Carlo (MCMC) estimation provides a flexible and efficient framework for modelling behavioural phenotypes. Next, we use data simulation to illustrate the potentially huge bias in estimating variance components on the basis of sum scores. We then apply the IRT approach with an analysis of attention problems in young adult twins where the variance decomposition model is extended with an IRT measurement model. We show that when estimating an IRT measurement model and a variance decomposition model simultaneously, the estimate for the heritability of attention problems increases from 40% (based on sum scores) to 73%. PMID:17534709

  10. IRT Model Selection Methods for Dichotomous Items

    ERIC Educational Resources Information Center

    Kang, Taehoon; Cohen, Allan S.

    2007-01-01

    Fit of the model to the data is important if the benefits of item response theory (IRT) are to be obtained. In this study, the authors compared model selection results using the likelihood ratio test, two information-based criteria, and two Bayesian methods. An example illustrated the potential for inconsistency in model selection depending on…

  11. New Method of Calibrating IRT Models.

    ERIC Educational Resources Information Center

    Jiang, Hai; Tang, K. Linda

    This discussion of new methods for calibrating item response theory (IRT) models looks into new optimization procedures, such as the Genetic Algorithm (GA) to improve on the use of the Newton-Raphson procedure. The advantages of using a global optimization procedure like GA is that this kind of procedure is not easily affected by local optima and…

  12. Understanding Parameter Invariance in Unidimensional IRT Models

    ERIC Educational Resources Information Center

    Rupp, Andre A.; Zumbo, Bruno D.

    2006-01-01

    One theoretical feature that makes item response theory (IRT) models those of choice for many psychometric data analysts is parameter invariance, the equality of item and examinee parameters from different examinee populations or measurement conditions. In this article, using the well-known fact that item and examinee parameters are identical only…

  13. Generalized IRT Models for Extreme Response Style

    ERIC Educational Resources Information Center

    Jin, Kuan-Yu; Wang, Wen-Chung

    2014-01-01

    Extreme response style (ERS) is a systematic tendency for a person to endorse extreme options (e.g., strongly disagree, strongly agree) on Likert-type or rating-scale items. In this study, we develop a new class of item response theory (IRT) models to account for ERS so that the target latent trait is free from the response style and the tendency…

  14. An Investigation of Item Fit Statistics for Mixed IRT Models

    ERIC Educational Resources Information Center

    Chon, Kyong Hee

    2009-01-01

    The purpose of this study was to investigate procedures for assessing model fit of IRT models for mixed format data. In this study, various IRT model combinations were fitted to data containing both dichotomous and polytomous item responses, and the suitability of the chosen model mixtures was evaluated based on a number of model fit procedures.…

  15. Skills Diagnosis Using IRT-Based Continuous Latent Trait Models

    ERIC Educational Resources Information Center

    Stout, William

    2007-01-01

    This article summarizes the continuous latent trait IRT approach to skills diagnosis as particularized by a representative variety of continuous latent trait models using item response functions (IRFs). First, several basic IRT-based continuous latent trait approaches are presented in some detail. Then a brief summary of estimation, model…

  16. A Comparison of Exposure Control Procedures in CATs Using the 3PL Model

    ERIC Educational Resources Information Center

    Leroux, Audrey J.; Lopez, Myriam; Hembry, Ian; Dodd, Barbara G.

    2013-01-01

    This study compares the progressive-restricted standard error (PR-SE) exposure control procedure to three commonly used procedures in computerized adaptive testing, the randomesque, Sympson-Hetter (SH), and no exposure control methods. The performance of these four procedures is evaluated using the three-parameter logistic model under the…

  17. Bayesian Estimation of the Logistic Positive Exponent IRT Model

    ERIC Educational Resources Information Center

    Bolfarine, Heleno; Bazan, Jorge Luis

    2010-01-01

    A Bayesian inference approach using Markov Chain Monte Carlo (MCMC) is developed for the logistic positive exponent (LPE) model proposed by Samejima and for a new skewed Logistic Item Response Theory (IRT) model, named Reflection LPE model. Both models lead to asymmetric item characteristic curves (ICC) and can be appropriate because a symmetric…

  18. A Comparison of Item Fit Statistics for Mixed IRT Models

    ERIC Educational Resources Information Center

    Chon, Kyong Hee; Lee, Won-Chan; Dunbar, Stephen B.

    2010-01-01

    In this study we examined procedures for assessing model-data fit of item response theory (IRT) models for mixed format data. The model fit indices used in this study include PARSCALE's G[superscript 2], Orlando and Thissen's S-X[superscript 2] and S-G[superscript 2], and Stone's chi[superscript 2*] and G[superscript 2*]. To investigate the…

  19. On the Bayesian Nonparametric Generalization of IRT-Type Models

    ERIC Educational Resources Information Center

    San Martin, Ernesto; Jara, Alejandro; Rolin, Jean-Marie; Mouchart, Michel

    2011-01-01

    We study the identification and consistency of Bayesian semiparametric IRT-type models, where the uncertainty on the abilities' distribution is modeled using a prior distribution on the space of probability measures. We show that for the semiparametric Rasch Poisson counts model, simple restrictions ensure the identification of a general…

  20. Bayesian Multidimensional IRT Models with a Hierarchical Structure

    ERIC Educational Resources Information Center

    Sheng, Yanyan; Wikle, Christopher K.

    2008-01-01

    As item response models gain increased popularity in large-scale educational and measurement testing situations, many studies have been conducted on the development and applications of unidimensional and multidimensional models. Recently, attention has been paid to IRT-based models with an overall ability dimension underlying several ability…

  1. A Multilevel Mixture IRT Model with an Application to DIF

    ERIC Educational Resources Information Center

    Cho, Sun-Joo; Cohen, Allan S.

    2010-01-01

    Mixture item response theory models have been suggested as a potentially useful methodology for identifying latent groups formed along secondary, possibly nuisance dimensions. In this article, we describe a multilevel mixture item response theory (IRT) model (MMixIRTM) that allows for the possibility that this nuisance dimensionality may function…

  2. Bias Coefficients for Lack of Invariance in Unidimensional IRT Models.

    ERIC Educational Resources Information Center

    Rupp, Andre A.; Zumbo, Bruno D.

    The feature that makes item response theory (IRT) models the models of choice for many psychometric data analysts is parameter invariance, the equality of item and examinee parameters from different populations. Using the well-known fact that item and examinee parameters are identical only up to a set of linear transformations specific to the…

  3. Local Dependence Diagnostics in IRT Modeling of Binary Data

    ERIC Educational Resources Information Center

    Liu, Yang; Maydeu-Olivares, Alberto

    2013-01-01

    Local dependence (LD) for binary IRT models can be diagnosed using Chen and Thissen's bivariate X[superscript 2] statistic and the score test statistics proposed by Glas and Suarez-Falcon, and Liu and Thissen. Alternatively, LD can be assessed using general purpose statistics such as bivariate residuals or Maydeu-Olivares and Joe's M[subscript r]…

  4. Bayesian Estimation of Multi-Unidimensional Graded Response IRT Models

    ERIC Educational Resources Information Center

    Kuo, Tzu-Chun

    2015-01-01

    Item response theory (IRT) has gained an increasing popularity in large-scale educational and psychological testing situations because of its theoretical advantages over classical test theory. Unidimensional graded response models (GRMs) are useful when polytomous response items are designed to measure a unified latent trait. They are limited in…

  5. Comparing Vertical Scales Derived from Dichotomous and Polytomous IRT Models for a Test Composed of Testlets.

    ERIC Educational Resources Information Center

    Bishop, N. Scott; Omar, Md Hafidz

    Previous research has shown that testlet structures often violate important assumptions of dichotomous item response theory (D-IRT) models, applied to item-level scores, that can in turn affect the results of many measurement applications. In this situation, polytomous IRT (P-IRT) models, applied to testlet-level scores, have been used as an…

  6. Assessing the Effect of Model-Data Misfit on the Invariance Property of IRT Parameter Estimates.

    ERIC Educational Resources Information Center

    Fan, Xitao; Ping, Yin

    This study empirically investigated the potential negative effect of item response theory (IRT) model-data misfit on the degree of invariance of: (1) IRT item parameter estimates (item difficulty and discrimination); and (2) IRT person ability parameter estimates. A large-scale statewide assessment program test database was used, for which the…

  7. A Componential IRT Model for Guilt.

    ERIC Educational Resources Information Center

    Smits, Dirk J. M.; De Boeck, Paul

    2003-01-01

    Studied the process structure of guilt with an adaptation of the Model with Internal Restrictions on Item Difficulty (R. Butter and others, 1998) administered to 270 high school students. Findings show that this kind of modeling is appropriate to investigate the structure of other emotions. (SLD)

  8. IRT Models for Ability-Based Guessing

    ERIC Educational Resources Information Center

    Martin, Ernesto San; del Pino, Guido; De Boeck, Paul

    2006-01-01

    An ability-based guessing model is formulated and applied to several data sets regarding educational tests in language and in mathematics. The formulation of the model is such that the probability of a correct guess does not only depend on the item but also on the ability of the individual, weighted with a general discrimination parameter. By so…

  9. Stochastic Ordering of the Latent Trait by the Sum Score Under Various Polytomous IRT Models

    ERIC Educational Resources Information Center

    van der Ark, L. Andries

    2005-01-01

    The sum score is often used to order respondents on the latent trait measured by the test. Therefore, it is desirable that under the chosen model the sum score stochastically orders the latent trait. It is known that unlike dichotomous item response theory (IRT) models, most polytomous IRT models do not imply stochastic ordering. It is unknown,…

  10. Application of an IRT Polytomous Model for Measuring Health Related Quality of Life

    ERIC Educational Resources Information Center

    Tejada, Antonio J. Rojas; Rojas, Oscar M. Lozano

    2005-01-01

    Background: The Item Response Theory (IRT) has advantages for measuring Health Related Quality of Life (HRQOL) as opposed to the Classical Tests Theory (CTT). Objectives: To present the results of the application of a polytomous model based on IRT, specifically, the Rating Scale Model (RSM), to measure HRQOL with the EORTC QLQ-C30. Methods: 103…

  11. Performance of the Generalized S-X[Superscript 2] Item Fit Index for Polytomous IRT Models

    ERIC Educational Resources Information Center

    Kang, Taehoon; Chen, Troy T.

    2008-01-01

    Orlando and Thissen's S-X[superscript 2] item fit index has performed better than traditional item fit statistics such as Yen' s Q[subscript 1] and McKinley and Mill' s G[superscript 2] for dichotomous item response theory (IRT) models. This study extends the utility of S-X[superscript 2] to polytomous IRT models, including the generalized partial…

  12. Why Should We Assess the Goodness-of-Fit of IRT Models?

    ERIC Educational Resources Information Center

    Maydeu-Olivares, Alberto

    2013-01-01

    In this rejoinder, Maydeu-Olivares states that, in item response theory (IRT) measurement applications, the application of goodness-of-fit (GOF) methods informs researchers of the discrepancy between the model and the data being fitted (the room for improvement). By routinely reporting the GOF of IRT models, together with the substantive results…

  13. Robustness of the Polytomous IRT Model to Violations of the Unidimensionality Assumption.

    ERIC Educational Resources Information Center

    Dawadi, Bhaskar R.

    The robustness of the polytomous Item Response Theory (IRT) model to violations of the unidimensionality assumption was studied. A secondary purpose was to provide guidelines to practitioners to help in deciding whether to use an IRT model to analyze their data. In a simulation study, the unidimensionality assumption was deliberately violated by…

  14. Comparing Accuracy of Parameter Estimation Using IRT Models in the Presence of Guessing

    ERIC Educational Resources Information Center

    Fu, Qiong

    2010-01-01

    This research investigated how the accuracy of person ability and item difficulty parameter estimation varied across five IRT models with respect to the presence of guessing, targeting, and varied combinations of sample sizes and test lengths. The data were simulated with 50 replications under each of the 18 combined conditions. Five IRT models…

  15. Standard Errors and Confidence Intervals from Bootstrapping for Ramsay-Curve Item Response Theory Model Item Parameters

    ERIC Educational Resources Information Center

    Gu, Fei; Skorupski, William P.; Hoyle, Larry; Kingston, Neal M.

    2011-01-01

    Ramsay-curve item response theory (RC-IRT) is a nonparametric procedure that estimates the latent trait using splines, and no distributional assumption about the latent trait is required. For item parameters of the two-parameter logistic (2-PL), three-parameter logistic (3-PL), and polytomous IRT models, RC-IRT can provide more accurate estimates…

  16. IRT Model Misspecification and Measurement of Growth in Vertical Scaling

    ERIC Educational Resources Information Center

    Bolt, Daniel M.; Deng, Sien; Lee, Sora

    2014-01-01

    Functional form misfit is frequently a concern in item response theory (IRT), although the practical implications of misfit are often difficult to evaluate. In this article, we illustrate how seemingly negligible amounts of functional form misfit, when systematic, can be associated with significant distortions of the score metric in vertical…

  17. Distinguishing Continuous and Discrete Approaches to Multilevel Mixture IRT Models: A Model Comparison Perspective

    ERIC Educational Resources Information Center

    Zhu, Xiaoshu

    2013-01-01

    The current study introduced a general modeling framework, multilevel mixture IRT (MMIRT) which detects and describes characteristics of population heterogeneity, while accommodating the hierarchical data structure. In addition to introducing both continuous and discrete approaches to MMIRT, the main focus of the current study was to distinguish…

  18. A Nonparametric Approach for Assessing Goodness-of-Fit of IRT Models in a Mixed Format Test

    ERIC Educational Resources Information Center

    Liang, Tie; Wells, Craig S.

    2015-01-01

    Investigating the fit of a parametric model plays a vital role in validating an item response theory (IRT) model. An area that has received little attention is the assessment of multiple IRT models used in a mixed-format test. The present study extends the nonparametric approach, proposed by Douglas and Cohen (2001), to assess model fit of three…

  19. The External Validity of Scores Based on the Two-Parameter Logistic Model: Some Comparisons between IRT and CTT

    ERIC Educational Resources Information Center

    Ferrando, Pere J.; Chico, Eliseo

    2007-01-01

    A theoretical advantage of item response theory (IRT) models is that trait estimates based on these models provide more test information than any other type of test score. It is still unclear, however, whether using IRT trait estimates improves external validity results in comparison with the results that can be obtained by using simple raw…

  20. IRT-ZIP Modeling for Multivariate Zero-Inflated Count Data

    ERIC Educational Resources Information Center

    Wang, Lijuan

    2010-01-01

    This study introduces an item response theory-zero-inflated Poisson (IRT-ZIP) model to investigate psychometric properties of multiple items and predict individuals' latent trait scores for multivariate zero-inflated count data. In the model, two link functions are used to capture two processes of the zero-inflated count data. Item parameters are…

  1. A Note on the Equivalence between Observed and Expected Information Functions with Polytomous IRT Models

    ERIC Educational Resources Information Center

    Magis, David

    2015-01-01

    The purpose of this note is to study the equivalence of observed and expected (Fisher) information functions with polytomous item response theory (IRT) models. It is established that observed and expected information functions are equivalent for the class of divide-by-total models (including partial credit, generalized partial credit, rating…

  2. Finite Mixture Multilevel Multidimensional Ordinal IRT Models for Large Scale Cross-Cultural Research

    ERIC Educational Resources Information Center

    de Jong, Martijn G.; Steenkamp, Jan-Benedict E. M.

    2010-01-01

    We present a class of finite mixture multilevel multidimensional ordinal IRT models for large scale cross-cultural research. Our model is proposed for confirmatory research settings. Our prior for item parameters is a mixture distribution to accommodate situations where different groups of countries have different measurement operations, while…

  3. A Unified Nonparametric IRT Model for "d"-Dimensional Psychological Test Data ("d"-Isop)

    ERIC Educational Resources Information Center

    Scheiblechner, Hartmann

    2007-01-01

    The (univariate) isotonic psychometric (ISOP) model (Scheiblechner, 1995) is a nonparametric IRT model for dichotomous and polytomous (rating scale) psychological test data. A weak subject independence axiom W1 postulates that the subjects are ordered in the same way except for ties (i.e., similarly or isotonically) by all items of a psychological…

  4. An Extension of Least Squares Estimation of IRT Linking Coefficients for the Graded Response Model

    ERIC Educational Resources Information Center

    Kim, Seonghoon

    2010-01-01

    The three types (generalized, unweighted, and weighted) of least squares methods, proposed by Ogasawara, for estimating item response theory (IRT) linking coefficients under dichotomous models are extended to the graded response model. A simulation study was conducted to confirm the accuracy of the extended formulas, and a real data study was…

  5. An Extension of IRT-Based Equating to the Dichotomous Testlet Response Theory Model

    ERIC Educational Resources Information Center

    Tao, Wei; Cao, Yi

    2016-01-01

    Current procedures for equating number-correct scores using traditional item response theory (IRT) methods assume local independence. However, when tests are constructed using testlets, one concern is the violation of the local item independence assumption. The testlet response theory (TRT) model is one way to accommodate local item dependence.…

  6. Immediate Feedback and Opportunity to Revise Answers: Application of a Graded Response IRT Model

    ERIC Educational Resources Information Center

    Attali, Yigal

    2011-01-01

    Recently, Attali and Powers investigated the usefulness of providing immediate feedback on the correctness of answers to constructed response questions and the opportunity to revise incorrect answers. This article introduces an item response theory (IRT) model for scoring revised responses to questions when several attempts are allowed. The model…

  7. Comparing Three Estimation Methods for the Three-Parameter Logistic IRT Model

    ERIC Educational Resources Information Center

    Lamsal, Sunil

    2015-01-01

    Different estimation procedures have been developed for the unidimensional three-parameter item response theory (IRT) model. These techniques include the marginal maximum likelihood estimation, the fully Bayesian estimation using Markov chain Monte Carlo simulation techniques, and the Metropolis-Hastings Robbin-Monro estimation. With each…

  8. Fitting IRT Models to Dichotomous and Polytomous Data: Assessing the Relative Model-Data Fit of Ideal Point and Dominance Models

    ERIC Educational Resources Information Center

    Tay, Louis; Ali, Usama S.; Drasgow, Fritz; Williams, Bruce

    2011-01-01

    This study investigated the relative model-data fit of an ideal point item response theory (IRT) model (the generalized graded unfolding model [GGUM]) and dominance IRT models (e.g., the two-parameter logistic model [2PLM] and Samejima's graded response model [GRM]) to simulated dichotomous and polytomous data generated from each of these models.…

  9. A generalized longitudinal mixture IRT model for measuring differential growth in learning environments.

    PubMed

    Kadengye, Damazo T; Ceulemans, Eva; Van den Noortgate, Wim

    2014-09-01

    This article describes a generalized longitudinal mixture item response theory (IRT) model that allows for detecting latent group differences in item response data obtained from electronic learning (e-learning) environments or other learning environments that result in large numbers of items. The described model can be viewed as a combination of a longitudinal Rasch model, a mixture Rasch model, and a random-item IRT model, and it includes some features of the explanatory IRT modeling framework. The model assumes the possible presence of latent classes in item response patterns, due to initial person-level differences before learning takes place, to latent class-specific learning trajectories, or to a combination of both. Moreover, it allows for differential item functioning over the classes. A Bayesian model estimation procedure is described, and the results of a simulation study are presented that indicate that the parameters are recovered well, particularly for conditions with large item sample sizes. The model is also illustrated with an empirical sample data set from a Web-based e-learning environment.

  10. Ramsay-Curve Item Response Theory for the Three-Parameter Logistic Item Response Model

    ERIC Educational Resources Information Center

    Woods, Carol M.

    2008-01-01

    In Ramsay-curve item response theory (RC-IRT), the latent variable distribution is estimated simultaneously with the item parameters of a unidimensional item response model using marginal maximum likelihood estimation. This study evaluates RC-IRT for the three-parameter logistic (3PL) model with comparisons to the normal model and to the empirical…

  11. A GPU-Based Gibbs Sampler for a Unidimensional IRT Model

    PubMed Central

    Welling, William S.; Zhu, Michelle M.

    2014-01-01

    Item response theory (IRT) is a popular approach used for addressing large-scale statistical problems in psychometrics as well as in other fields. The fully Bayesian approach for estimating IRT models is usually memory and computationally expensive due to the large number of iterations. This limits the use of the procedure in many applications. In an effort to overcome such restraint, previous studies focused on utilizing the message passing interface (MPI) in a distributed memory-based Linux cluster to achieve certain speedups. However, given the high data dependencies in a single Markov chain for IRT models, the communication overhead rapidly grows as the number of cluster nodes increases. This makes it difficult to further improve the performance under such a parallel framework. This study aims to tackle the problem using massive core-based graphic processing units (GPU), which is practical, cost-effective, and convenient in actual applications. The performance comparisons among serial CPU, MPI, and compute unified device architecture (CUDA) programs demonstrate that the CUDA GPU approach has many advantages over the CPU-based approach and therefore is preferred. PMID:27355058

  12. A GPU-Based Gibbs Sampler for a Unidimensional IRT Model.

    PubMed

    Sheng, Yanyan; Welling, William S; Zhu, Michelle M

    2014-01-01

    Item response theory (IRT) is a popular approach used for addressing large-scale statistical problems in psychometrics as well as in other fields. The fully Bayesian approach for estimating IRT models is usually memory and computationally expensive due to the large number of iterations. This limits the use of the procedure in many applications. In an effort to overcome such restraint, previous studies focused on utilizing the message passing interface (MPI) in a distributed memory-based Linux cluster to achieve certain speedups. However, given the high data dependencies in a single Markov chain for IRT models, the communication overhead rapidly grows as the number of cluster nodes increases. This makes it difficult to further improve the performance under such a parallel framework. This study aims to tackle the problem using massive core-based graphic processing units (GPU), which is practical, cost-effective, and convenient in actual applications. The performance comparisons among serial CPU, MPI, and compute unified device architecture (CUDA) programs demonstrate that the CUDA GPU approach has many advantages over the CPU-based approach and therefore is preferred.

  13. SIMPOLYCAT: An SAS Program for Conducting CAT Simulation Based on Polytomous IRT Models

    PubMed Central

    Chen, Ssu-Kuang; Cook, Karon F.

    2009-01-01

    A real-data simulation of computerized adaptive testing (CAT) is an important step in real life CAT applications. Such a simulation allows CAT developers to evaluate important features of the CAT system such as item selection and stopping rules before live testing. SIMPOLYCAT, an SAS macro program, was created by the authors to conduct real-data CAT simulation based on polytomous item response theory (IRT) models. In SIMPOLYCAT, item responses can be input from an external file or generated internally based on item parameters provided by users. The program allows users to choose among methods of setting initial θ, approaches to item selection, trait estimators, CAT stopping criteria, polytomous IRT models, and other CAT parameters. In addition, CAT simulation results can be saved easily and used for further study. The purpose of this article is to introduce SIMPOLYCAT, briefly describe the program algorithm and parameters, and provide examples of CAT simulations using generated and real data. Visual comparisons of the results obtained from the CAT simulations are presented. PMID:19363190

  14. Investigating a Weakly Informative Prior for Item Scale Hyperparameters in Hierarchical 3PNO IRT Models.

    PubMed

    Sheng, Yanyan

    2017-01-01

    The half-t family has been suggested for the scale hyperparameter in Bayesian hierarchical modeling. Two parameters define a half-t distribution: the scale s and the degree-of-freedom ν. When s is set at a finite value that is slightly larger than the actual standard deviation of the parameters, the half-t prior density can be vaguely informative. This paper focused on such densities, and applied them to the hierarchical three-parameter item response theory (IRT) model. Monte Carlo simulations were carried out to investigate the performance of such specifications in parameter recovery and model comparisons under situations where the actual variability of item parameters varied, and results suggest that the half-t family does offer advantages over the commonly adopted uniform or inverse-gamma prior density by allowing the variability for item parameters to be either very small or large. A real data example is also provided to further illustrate this.

  15. Investigating a Weakly Informative Prior for Item Scale Hyperparameters in Hierarchical 3PNO IRT Models

    PubMed Central

    Sheng, Yanyan

    2017-01-01

    The half-t family has been suggested for the scale hyperparameter in Bayesian hierarchical modeling. Two parameters define a half-t distribution: the scale s and the degree-of-freedom ν. When s is set at a finite value that is slightly larger than the actual standard deviation of the parameters, the half-t prior density can be vaguely informative. This paper focused on such densities, and applied them to the hierarchical three-parameter item response theory (IRT) model. Monte Carlo simulations were carried out to investigate the performance of such specifications in parameter recovery and model comparisons under situations where the actual variability of item parameters varied, and results suggest that the half-t family does offer advantages over the commonly adopted uniform or inverse-gamma prior density by allowing the variability for item parameters to be either very small or large. A real data example is also provided to further illustrate this. PMID:28220096

  16. Comparing Different Approaches of Bias Correction for Ability Estimation in IRT Models. Research Report. ETS RR-08-13

    ERIC Educational Resources Information Center

    Lee, Yi-Hsuan; Zhang, Jinming

    2008-01-01

    The method of maximum-likelihood is typically applied to item response theory (IRT) models when the ability parameter is estimated while conditioning on the true item parameters. In practice, the item parameters are unknown and need to be estimated first from a calibration sample. Lewis (1985) and Zhang and Lu (2007) proposed the expected response…

  17. Pretest-Posttest-Posttest Multilevel IRT Modeling of Competence Growth of Students in Higher Education in Germany

    ERIC Educational Resources Information Center

    Schmidt, Susanne; Zlatkin-Troitschanskaia, Olga; Fox, Jean-Paul

    2016-01-01

    Longitudinal research in higher education faces several challenges. Appropriate methods of analyzing competence growth of students are needed to deal with those challenges and thereby obtain valid results. In this article, a pretest-posttest-posttest multivariate multilevel IRT model for repeated measures is introduced which is designed to address…

  18. Efficient Full Information Maximum Likelihood Estimation for Multidimensional IRT Models. Research Report. ETS RR-09-03

    ERIC Educational Resources Information Center

    Rijmen, Frank

    2009-01-01

    Maximum marginal likelihood estimation of multidimensional item response theory (IRT) models has been hampered by the calculation of the multidimensional integral over the ability distribution. However, the researcher often has a specific hypothesis about the conditional (in)dependence relations among the latent variables. Exploiting these…

  19. A Comparison of Three IRT Approaches to Examinee Ability Change Modeling in a Single-Group Anchor Test Design

    ERIC Educational Resources Information Center

    Paek, Insu; Park, Hyun-Jeong; Cai, Li; Chi, Eunlim

    2014-01-01

    Typically a longitudinal growth modeling based on item response theory (IRT) requires repeated measures data from a single group with the same test design. If operational or item exposure problems are present, the same test may not be employed to collect data for longitudinal analyses and tests at multiple time points are constructed with unique…

  20. Mixture Random-Effect IRT Models for Controlling Extreme Response Style on Rating Scales

    PubMed Central

    Huang, Hung-Yu

    2016-01-01

    Respondents are often requested to provide a response to Likert-type or rating-scale items during the assessment of attitude, interest, and personality to measure a variety of latent traits. Extreme response style (ERS), which is defined as a consistent and systematic tendency of a person to locate on a limited number of available rating-scale options, may distort the test validity. Several latent trait models have been proposed to address ERS, but all these models have limitations. Mixture random-effect item response theory (IRT) models for ERS are developed in this study to simultaneously identify the mixtures of latent classes from different ERS levels and detect the possible differential functioning items that result from different latent mixtures. The model parameters can be recovered fairly well in a series of simulations that use Bayesian estimation with the WinBUGS program. In addition, the model parameters in the developed models can be used to identify items that are likely to elicit ERS. The results show that a long test and large sample can improve the parameter estimation process; the precision of the parameter estimates increases with the number of response options, and the model parameter estimation outperforms the person parameter estimation. Ignoring the mixtures and ERS results in substantial rank-order changes in the target latent trait and a reduced classification accuracy of the response styles. An empirical survey of emotional intelligence in college students is presented to demonstrate the applications and implications of the new models. PMID:27853444

  1. Detecting intervention effects using a multilevel latent transition analysis with a mixture IRT model.

    PubMed

    Cho, Sun-Joo; Cohen, Allan S; Bottge, Brian

    2013-07-01

    A multilevel latent transition analysis (LTA) with a mixture IRT measurement model (MixIRTM) is described for investigating the effectiveness of an intervention. The addition of a MixIRTM to the multilevel LTA permits consideration of both potential heterogeneity in students' response to instructional intervention as well as a methodology for assessing stage sequential change over time at both student and teacher levels. Results from an LTA-MixIRTM and multilevel LTA-MixIRTM were compared in the context of an educational intervention study. Both models were able to describe homogeneities in problem solving and transition patterns. However, ignoring a multilevel structure in LTA-MixIRTM led to different results in group membership assignment in empirical results. Results for the multilevel LTA-MixIRTM indicated that there were distinct individual differences in the different transition patterns. The students receiving the intervention treatment outscored their business as usual (i.e., control group) counterparts on the curriculum-based Fractions Computation test. In addition, 27.4 % of the students in the sample moved from the low ability student-level latent class to the high ability student-level latent class. Students were characterized differently depending on the teacher-level latent class.

  2. Using a Mixed IRT Model to Assess the Scale Usage in the Measurement of Job Satisfaction.

    PubMed

    Kutscher, Tanja; Crayen, Claudia; Eid, Michael

    2016-01-01

    This study investigated the adequacy of a rating scale with a large number of response categories that is often used in panel surveys for assessing diverse aspects of job satisfaction. An inappropriate scale usage is indicative of overstraining respondents and of diminished psychometric scale quality. The mixed Item Response Theory (IRT) approach for polytomous data allows exploring heterogeneous patterns of inappropriate scale usage in form of avoided categories and response styles. In this study, panel data of employees (n = 7036) on five aspects of job satisfaction measured on an 11-point rating scale within the "Household, Income and Labor Dynamics in Australia" (wave 2001) were analyzed. A three-class solution of the restricted mixed generalized partial credit model fit the data best. The results showed that in no class the 11-point scale was appropriately used but that the number of categories used was reduced in all three classes. Respondents of the large class (40%) appropriately differentiate between up to six categories. The two smaller classes (33 and 27%) avoid even more categories and show some kind of extreme response style. Furthermore, classes differ in socio-demographic and job-related factors. In conclusion, a two- to six-point scale without the middle point might be more adequate for assessing job satisfaction.

  3. Using a Mixed IRT Model to Assess the Scale Usage in the Measurement of Job Satisfaction

    PubMed Central

    Kutscher, Tanja; Crayen, Claudia; Eid, Michael

    2017-01-01

    This study investigated the adequacy of a rating scale with a large number of response categories that is often used in panel surveys for assessing diverse aspects of job satisfaction. An inappropriate scale usage is indicative of overstraining respondents and of diminished psychometric scale quality. The mixed Item Response Theory (IRT) approach for polytomous data allows exploring heterogeneous patterns of inappropriate scale usage in form of avoided categories and response styles. In this study, panel data of employees (n = 7036) on five aspects of job satisfaction measured on an 11-point rating scale within the “Household, Income and Labor Dynamics in Australia” (wave 2001) were analyzed. A three-class solution of the restricted mixed generalized partial credit model fit the data best. The results showed that in no class the 11-point scale was appropriately used but that the number of categories used was reduced in all three classes. Respondents of the large class (40%) appropriately differentiate between up to six categories. The two smaller classes (33 and 27%) avoid even more categories and show some kind of extreme response style. Furthermore, classes differ in socio-demographic and job-related factors. In conclusion, a two- to six-point scale without the middle point might be more adequate for assessing job satisfaction. PMID:28101067

  4. IRT Item Parameter Recovery with Marginal Maximum Likelihood Estimation Using Loglinear Smoothing Models

    ERIC Educational Resources Information Center

    Casabianca, Jodi M.; Lewis, Charles

    2015-01-01

    Loglinear smoothing (LLS) estimates the latent trait distribution while making fewer assumptions about its form and maintaining parsimony, thus leading to more precise item response theory (IRT) item parameter estimates than standard marginal maximum likelihood (MML). This article provides the expectation-maximization algorithm for MML estimation…

  5. IRT Equating of the MCAT. MCAT Monograph.

    ERIC Educational Resources Information Center

    Hendrickson, Amy B.; Kolen, Michael J.

    This study compared various equating models and procedures for a sample of data from the Medical College Admission Test(MCAT), considering how item response theory (IRT) equating results compare with classical equipercentile results and how the results based on use of various IRT models, observed score versus true score, direct versus linked…

  6. Ramsay Curve IRT for Likert-Type Data

    ERIC Educational Resources Information Center

    Woods, Carol M.

    2007-01-01

    Ramsay curve item response theory (RC-IRT) was recently developed to detect and correct for nonnormal latent variables when unidimensional IRT models are fitted to data using maximum marginal likelihood estimation. The purpose of this research is to evaluate the performance of RC-IRT for Likert-type item responses with varying test lengths, sample…

  7. An IRT Approach to Constructing and Scoring Pairwise Preference Items Involving Stimuli on Different Dimensions: The Multi-Unidimensional Pairwise-Preference Model

    ERIC Educational Resources Information Center

    Stark, Stephen; Chernyshenko, Oleksandr S.; Drasgow, Fritz

    2005-01-01

    This article proposes an item response theory (IRT) approach to constructing and scoring multidimensional pairwise preference items. Individual statements are administered and calibrated using a unidimensional single-stimulus model. Tests are created by combining multidimensional items with a small number of unidimensional pairings needed to…

  8. Partially Observed Mixtures of IRT Models: An Extension of the Generalized Partial-Credit Model

    ERIC Educational Resources Information Center

    Von Davier, Matthias; Yamamoto, Kentaro

    2004-01-01

    The generalized partial-credit model (GPCM) is used frequently in educational testing and in large-scale assessments for analyzing polytomous data. Special cases of the generalized partial-credit model are the partial-credit model--or Rasch model for ordinal data--and the two parameter logistic (2PL) model. This article extends the GPCM to the…

  9. An Investigation of the Performance of the Generalized S-X[superscript 2] Item-Fit Index for Polytomous IRT Models. ACT Research Report Series, 2007-1

    ERIC Educational Resources Information Center

    Kang, Taehoon; Chen, Troy T.

    2007-01-01

    Orlando and Thissen (2000, 2003) proposed an item-fit index, S-X[superscript 2], for dichotomous item response theory (IRT) models, which has performed better than traditional item-fit statistics such as Yen's (1981) Q[subscript 1] and McKinley and Mill's (1985) G[superscript 2]. This study extends the utility of S-X[superscript 2] to polytomous…

  10. Infrared Thermometer (IRT) Handbook

    SciTech Connect

    VR Morris

    2006-10-30

    The Infrared Thermometer (IRT) is a ground-based radiation pyrometer that provides measurements of the equivalent blackbody brightness temperature of the scene in its field of view. The downwelling version has a narrow field of view for measuring sky temperature and for detecting clouds. The upwelling version has a wide field of view for measuring the narrowband radiating temperature of the ground surface.

  11. MCMC Estimation of Multidimensional IRT Models. Research Report 98-14.

    ERIC Educational Resources Information Center

    Beguin, Anton A.; Glas, Cees A. W.

    A Bayesian procedure to estimate the three-parameter normal ogive model and a generalization to a model with multidimensional ability parameters are discussed. The procedure is a generalization of a procedure by J. Albert (1992) for estimating the two-parameter normal ogive model. The procedure will support multiple samples from multiple…

  12. Using Spreadsheets To Implement the One-Parameter Item Response Theory (IRT) Model.

    ERIC Educational Resources Information Center

    Henard, David H.

    Item response theory models arose from the inherent limitations of classical test theory methods of test analysis. A brief description of those limitations and the corresponding enhancements provided by item response models is provided. Further, an examination of the popular Rasch one-parameter latent trait model is undertaken. Specific…

  13. On the Relationships between Jeffreys Modal and Weighted Likelihood Estimation of Ability under Logistic IRT Models

    ERIC Educational Resources Information Center

    Magis, David; Raiche, Gilles

    2012-01-01

    This paper focuses on two estimators of ability with logistic item response theory models: the Bayesian modal (BM) estimator and the weighted likelihood (WL) estimator. For the BM estimator, Jeffreys' prior distribution is considered, and the corresponding estimator is referred to as the Jeffreys modal (JM) estimator. It is established that under…

  14. Asymptotic Standard Errors of Observed-Score Equating with Polytomous IRT Models

    ERIC Educational Resources Information Center

    Andersson, Björn

    2016-01-01

    In observed-score equipercentile equating, the goal is to make scores on two scales or tests measuring the same construct comparable by matching the percentiles of the respective score distributions. If the tests consist of different items with multiple categories for each item, a suitable model for the responses is a polytomous item response…

  15. Effect Size Measures for Differential Item Functioning in a Multidimensional IRT Model

    ERIC Educational Resources Information Center

    Suh, Youngsuk

    2016-01-01

    This study adapted an effect size measure used for studying differential item functioning (DIF) in unidimensional tests and extended the measure to multidimensional tests. Two effect size measures were considered in a multidimensional item response theory model: signed weighted P-difference and unsigned weighted P-difference. The performance of…

  16. Validity of Multiprocess IRT Models for Separating Content and Response Styles

    ERIC Educational Resources Information Center

    Plieninger, Hansjörg; Meiser, Thorsten

    2014-01-01

    Response styles, the tendency to respond to Likert-type items irrespective of content, are a widely known threat to the reliability and validity of self-report measures. However, it is still debated how to measure and control for response styles such as extreme responding. Recently, multiprocess item response theory models have been proposed that…

  17. A Class of Multidimensional IRT Models for Testing Unidimensionality and Clustering Items

    ERIC Educational Resources Information Center

    Bartolucci, Francesco

    2007-01-01

    We illustrate a class of multidimensional item response theory models in which the items are allowed to have different discriminating power and the latent traits are represented through a vector having a discrete distribution. We also show how the hypothesis of unidimensionality may be tested against a specific bidimensional alternative by using a…

  18. Combining IRT and SEM: A Hybrid Model for Fitting Responses and Response Certainties

    ERIC Educational Resources Information Center

    Ferrando, Pere J.; Anguiano-Carrasco, Cristina; Demestre, Josep

    2013-01-01

    This article proposes a model-based procedure, intended for personality measures, for exploiting the auxiliary information provided by the certainty with which individuals answer every item (response certainty). This information is used to (a) obtain more accurate estimates of individual trait levels, and (b) provide a more detailed assessment of…

  19. Partial likelihood estimation of IRT models with censored lifetime data: an application to mental disorders in the ESEMeD surveys.

    PubMed

    Forero, Carlos G; Almansa, Josué; Adroher, Núria D; Vermunt, Jeroen K; Vilagut, Gemma; De Graaf, Ron; Haro, Josep-Maria; Alonso Caballero, Jordi

    2014-07-01

    Developmental studies of mental disorders based on epidemiological data are often based on cross-sectional retrospective surveys. Under such designs, observations are right-censored, causing underestimation of lifetime prevalences and correlations, and inducing bias in latent trait models on the observations. In this paper we propose a Partial Likelihood (PL) method to estimate unbiased IRT models of lifetime predisposition to develop a certain outcome. A two-step estimation procedure corrects the IRT likelihood of outcome appearance with a function depending on (a) projected outcome frequencies at the end of the risk period, and (b) outcome censoring status at the time of the observation. Simulation results showed that the PL method yielded good recovery of true frequencies and intercepts. Slopes were best estimated when events were sufficiently correlated. When PL is applied to lifetime mental health disorders (assessed in the ESEMeD project surveys), estimated univariate prevalences were, on average, 1.4 times above raw estimates, and 2.06 higher in the case of bivariate prevalences.

  20. Arabidopsis IRT2 cooperates with the high-affinity iron uptake system to maintain iron homeostasis in root epidermal cells.

    PubMed

    Vert, Grégory; Barberon, Marie; Zelazny, Enric; Séguéla, Mathilde; Briat, Jean-François; Curie, Catherine

    2009-05-01

    Iron is an essential nutrient for all organisms but toxic when present in excess. Consequently, plants carefully regulate their iron uptake, dependent on the FRO2 ferric reductase and the IRT1 transporter, to control its homeostasis. Arabidopsis IRT2 gene, whose expression is induced in root epidermis upon iron deprivation, was shown to encode a functional iron/zinc transporter in yeast, and proposed to function in iron acquisition from the soil. In this study, we demonstrate that, unlike its close homolog IRT1, IRT2 is not involved in iron absorption from the soil since overexpression of IRT2 does not rescue the iron uptake defect of irt1-1 mutant and since a null irt2 mutant shows no chlorosis in low iron. Consistently, an IRT2-green fluorescent fusion protein, transiently expressed in culture cells, localizes to intracellular vesicles. However, IRT2 appears strictly co-regulated with FRO2 and IRT1, supporting the view that IRT2 is an integral component of the root response to iron deficiency in root epidermal cells. We propose a model where IRT2 likely prevents toxicity from IRT1-dependent iron fluxes in epidermal cells, through compartmentalization.

  1. Ramsay-Curve Item Response Theory (RC-IRT) to Detect and Correct for Nonnormal Latent Variables

    ERIC Educational Resources Information Center

    Woods, Carol M.

    2006-01-01

    Popular methods for fitting unidimensional item response theory (IRT) models to data assume that the latent variable is normally distributed in the population of respondents, but this can be unreasonable for some variables. Ramsay-curve IRT (RC-IRT) was developed to detect and correct for this nonnormality. The primary aims of this article are to…

  2. Modeling filters for formation of mono-energetic neutron beams in the research reactor IRT MEPhI and optimization of radiation shielding for liquid-xenon detector

    SciTech Connect

    Ivakhin, S. V.; Tikhomirov, G. V.; Bolozdynya, A. I.; Efremenko, Y. V.; Akimov, D. Y.; Stekhanov, V. N.

    2012-07-01

    The paper considers formation of mono-energetic neutron beams at the entrance of experimental channels in research reactors for various applications. The problem includes the following steps: 1. Full-scale mathematical model of the research IRT MEPhI was developed for numerical evaluations of neutron spectra and neutron spatial distribution in the area of experimental channels. 2. Modeling of filters in the channel to shift neutron spectrum towards the required mono-energetic line was performed. 3. Some characteristics of neutron beams at the entrance of detector were evaluated. The filter materials were selected. The calculations were carried out with application of the computer code based on the high-precision Monte-Carlo code MCNP. As a result, mathematical model was created for the filter which is able to form mono-energetic (24 keV) neutron beam. The study was carried out within the frames of the research project on development of Russian emission detector with liquid noble gas to observe rare processes of neutrino scattering and particles of hypothetical dark matter in atomic nuclei. (authors)

  3. A Combined IRT and SEM Approach for Individual-Level Assessment in Test-Retest Studies

    ERIC Educational Resources Information Center

    Ferrando, Pere J.

    2015-01-01

    The standard two-wave multiple-indicator model (2WMIM) commonly used to analyze test-retest data provides information at both the group and item level. Furthermore, when applied to binary and graded item responses, it is related to well-known item response theory (IRT) models. In this article the IRT-2WMIM relations are used to obtain additional…

  4. Item Response Theory with Covariates (IRT-C): Assessing Item Recovery and Differential Item Functioning for the Three-Parameter Logistic Model

    ERIC Educational Resources Information Center

    Tay, Louis; Huang, Qiming; Vermunt, Jeroen K.

    2016-01-01

    In large-scale testing, the use of multigroup approaches is limited for assessing differential item functioning (DIF) across multiple variables as DIF is examined for each variable separately. In contrast, the item response theory with covariate (IRT-C) procedure can be used to examine DIF across multiple variables (covariates) simultaneously. To…

  5. Further Empirical Results on Parametric Versus Non-Parametric IRT Modeling of Likert-Type Personality Data

    ERIC Educational Resources Information Center

    Maydeu-Olivares, Albert

    2005-01-01

    Chernyshenko, Stark, Chan, Drasgow, and Williams (2001) investigated the fit of Samejima's logistic graded model and Levine's non-parametric MFS model to the scales of two personality questionnaires and found that the graded model did not fit well. We attribute the poor fit of the graded model to small amounts of multidimensionality present in…

  6. IRT-Estimated Reliability for Tests Containing Mixed Item Formats

    ERIC Educational Resources Information Center

    Shu, Lianghua; Schwarz, Richard D.

    2014-01-01

    As a global measure of precision, item response theory (IRT) estimated reliability is derived for four coefficients (Cronbach's a, Feldt-Raju, stratified a, and marginal reliability). Models with different underlying assumptions concerning test-part similarity are discussed. A detailed computational example is presented for the targeted…

  7. Evaluation of the IRT Parameter Invariance Property for the MCAT.

    ERIC Educational Resources Information Center

    Kelkar, Vinaya; Wightman, Linda F.; Luecht, Richard M.

    The purpose of this study was to investigate the viability of the property of parameter invariance for the one-parameter (1P), two-parameter (2P), and three-parameter (3P) item response theory (IRT) models for the Medical College Admissions Tests (MCAT). Invariance of item parameters across different gender, ethnic, and language groups and the…

  8. The Impact of Different Ability Distributions on IRT Preequating.

    ERIC Educational Resources Information Center

    Stocking, Martha L.; Eignor, Daniel R.

    In item response theory (IRT), preequating depends upon item parameter estimate invariance. Three separate simulations, all using the unidimensional three-parameter logistic item response model, were conducted to study the impact of the following variables on preequating: (1) mean differences in ability; (2) multidimensionality in the data; and…

  9. Monoubiquitin-dependent endocytosis of the iron-regulated transporter 1 (IRT1) transporter controls iron uptake in plants.

    PubMed

    Barberon, Marie; Zelazny, Enric; Robert, Stéphanie; Conéjéro, Geneviève; Curie, Cathy; Friml, Jìrí; Vert, Grégory

    2011-08-09

    Plants take up iron from the soil using the iron-regulated transporter 1 (IRT1) high-affinity iron transporter at the root surface. Sophisticated regulatory mechanisms allow plants to tightly control the levels of IRT1, ensuring optimal absorption of essential but toxic iron. Here, we demonstrate that overexpression of Arabidopsis thaliana IRT1 leads to constitutive IRT1 protein accumulation, metal overload, and oxidative stress. IRT1 is unexpectedly found in trans-Golgi network/early endosomes of root hair cells, and its levels and localization are unaffected by iron nutrition. Using pharmacological approaches, we show that IRT1 cycles to the plasma membrane to perform iron and metal uptake at the cell surface and is sent to the vacuole for proper turnover. We also prove that IRT1 is monoubiquitinated on several cytosol-exposed residues in vivo and that mutation of two putative monoubiquitination target residues in IRT1 triggers stabilization at the plasma membrane and leads to extreme lethality. Together, these data suggest a model in which monoubiquitin-dependent internalization/sorting and turnover keep the plasma membrane pool of IRT1 low to ensure proper iron uptake and to prevent metal toxicity. More generally, our work demonstrates the existence of monoubiquitin-dependent trafficking to lytic vacuoles in plants and points to proteasome-independent turnover of plasma membrane proteins.

  10. Carbon Stars in the IRTS Survey

    NASA Astrophysics Data System (ADS)

    Le Bertre, T.; Tanaka, M.; Yamamura, I.; Murakami, H.; MacConnell, D.; Guertin, A.

    The near-infrared spectro-photometric survey of the Japanese experiment IRTS (Infrared Telescope in Space) has revealed 139 carbon stars from the presence of characteristic molecular absorption bands, in particular the 3.1 μm band due to a blend of C2H2 and HCN. For the IRTS carbon stars, we find a trend relating the 3.1 μm band strength to the K -L color index, which is known to correlate with mass-loss rate. This relation shows that the mass-loss intensity of cool giants is related to their stellar atmosphere extension. The IRTS experiment demonstrates that an extensive spectro-photometric survey in the near-infrared range (1-5 μm) would be extremely fruitful to identify late-type stars, giants as well as dwarfs, including brown dwarfs of the solar neighborhood, and to simultaneously characterize their properties.

  11. The Infrared Telescope in Space (IRTS)

    NASA Technical Reports Server (NTRS)

    Murakami, H.; Bock, J.; Freund, M. M.; Guo, H.; Hirao, T.; Lange, A. E.; Matsuhara, H.; Matsumoto, T.; Matsuura, S.; Mcmahon, T. J.

    1994-01-01

    The Infrared Telescope in Space (IRTS) is a cryogenically cooled small infrared telescope that will fly aboard the small space platform Space Flyer Unit. It will survey approximately 10% of the sky with a relatively wide beam during its 20 day emission. Four focal-plane instruments will make simultaneous observations of the sky at wavelengths ranging from 1 to 1000 microns. The IRTS will provide significant information on cosmology, interstellar matter, late-type stars, and interplanetary dust. This paper describes the instrumentation and mission.

  12. IRTS observation of zodiacal light and emission

    NASA Technical Reports Server (NTRS)

    Matsumoto, T.; Murakami, H.; Onaka, T.; Ootsubo, T.; Roellig, T. L.; Chan, K. -W.; Noda, M.

    1998-01-01

    We present the infrared spectrum of the zodiacal light and emission obtained by the Near-Infrared Spectrometer (NIRS) and Mid-Infrared Spectrometer (MIRS) onboard the Infrared Telescope in Space (IRTS). The wavelength coverages and spectral resolutions are 1.4-4.0 microns and 0.12 microns for the NIRS, and 4.5-11.7 microns and 0.23-0.36 microns for the MIRS respectively. Both instruments have the same beam size of 8 arcminutes square. The IRTS observations were made for 1995 March 29 - April 26. Here we present the data of two days, April 19 and April 20.

  13. A Comparison of IRT Linking Procedures

    ERIC Educational Resources Information Center

    Lee, Won-Chan; Ban, Jae-Chun

    2010-01-01

    Various applications of item response theory often require linking to achieve a common scale for item parameter estimates obtained from different groups. This article used a simulation to examine the relative performance of four different item response theory (IRT) linking procedures in a random groups equating design: concurrent calibration with…

  14. Detecting DIF in Polytomous Items Using MACS, IRT and Ordinal Logistic Regression

    ERIC Educational Resources Information Center

    Elosua, Paula; Wells, Craig

    2013-01-01

    The purpose of the present study was to compare the Type I error rate and power of two model-based procedures, the mean and covariance structure model (MACS) and the item response theory (IRT), and an observed-score based procedure, ordinal logistic regression, for detecting differential item functioning (DIF) in polytomous items. A simulation…

  15. Formal Relations and an Empirical Comparison among the Bi-Factor, the Testlet, and a Second-Order Multidimensional IRT Model

    ERIC Educational Resources Information Center

    Rijmen, Frank

    2010-01-01

    Testlet effects can be taken into account by incorporating specific dimensions in addition to the general dimension into the item response theory model. Three such multidimensional models are described: the bi-factor model, the testlet model, and a second-order model. It is shown how the second-order model is formally equivalent to the testlet…

  16. Testing Measurement Invariance: A Comparison of Multiple-Group Categorical CFA and IRT

    ERIC Educational Resources Information Center

    Kim, Eun Sook; Yoon, Myeongsun

    2011-01-01

    This study investigated two major approaches in testing measurement invariance for ordinal measures: multiple-group categorical confirmatory factor analysis (MCCFA) and item response theory (IRT). Unlike the ordinary linear factor analysis, MCCFA can appropriately model the ordered-categorical measures with a threshold structure. A simulation…

  17. Assessing the Item Response Theory with Covariate (IRT-C) Procedure for Ascertaining Differential Item Functioning

    ERIC Educational Resources Information Center

    Tay, Louis; Vermunt, Jeroen K.; Wang, Chun

    2013-01-01

    We evaluate the item response theory with covariates (IRT-C) procedure for assessing differential item functioning (DIF) without preknowledge of anchor items (Tay, Newman, & Vermunt, 2011). This procedure begins with a fully constrained baseline model, and candidate items are tested for uniform and/or nonuniform DIF using the Wald statistic.…

  18. Empirical vs. Expected IRT-Based Reliability Estimation in Computerized Multistage Testing (MST)

    ERIC Educational Resources Information Center

    Zhang, Yanwei; Breithaupt, Krista; Tessema, Aster; Chuah, David

    2006-01-01

    Two IRT-based procedures to estimate test reliability for a certification exam that used both adaptive (via a MST model) and non-adaptive design were considered in this study. Both procedures rely on calibrated item parameters to estimate error variance. In terms of score variance, one procedure (Method 1) uses the empirical ability distribution…

  19. Using IRT Trait Estimates versus Summated Scores in Predicting Outcomes

    ERIC Educational Resources Information Center

    Xu, Ting; Stone, Clement A.

    2012-01-01

    It has been argued that item response theory trait estimates should be used in analyses rather than number right (NR) or summated scale (SS) scores. Thissen and Orlando postulated that IRT scaling tends to produce trait estimates that are linearly related to the underlying trait being measured. Therefore, IRT trait estimates can be more useful…

  20. Study of experimental parameters for IRT applications in building elements using multi-layered analytical solutions

    NASA Astrophysics Data System (ADS)

    Serra, Catarina; Simões, Nuno; Tadeu, António

    2015-05-01

    This paper compares experimental and heat transfer modeling results for thermography applications in building elements. Over the years most building envelope inspections using infrared thermography (IRT) have been focused on qualitative analysis using mostly passive thermography techniques. However, increased need for the monitorization and assessment of the energy performance and thermal behavior of buildings, along with ongoing structural safety concerns, has raised interest in quantitative studies and active IRT applications in buildings. Numerous other fields have benefited from developments in defect detection studies and from countless non-destructive testing applications. Pulse phase thermography, in which phase images are studied (instead of temperature images) using a long heating pulse have been proposed to be the most effective for Civil Engineering applications. However, the particular characteristics of building elements and materials, along with the complex nature of heat transfer phenomena, demand specific experimental procedures and processing techniques. In this paper, analytical solutions to simulate heat transfer in the frequency domain in multi-layered media are used to compute thermal wave phase results. These are compared to experimental IRT phase analysis results of experiments performed on test specimens simulating building elements with embedded defects. Crucial test parameters such as test duration and defect characteristics are changed and their influence is studied. In this way, this paper contributes to the understanding of building envelope thermal patterns using active IRT in defect detection studies and to the definition of test parameters.

  1. Raman scattering of IrTe2

    NASA Astrophysics Data System (ADS)

    Lee, Alexander; Thorsmolle, Verner; Artyukhin, Sergey; Yang, Jun; Cheong, Sang-Wook; Blumberg, Girsh

    2014-03-01

    IrTe2 presents a layered compound with a triangular lattice. It is known to exhibit a first order structural phase transition at approximately 260 K which is of a first order, corresponding to a formation of a superstructure with a period of five unit cells. Using polarized Raman spectroscopy we have studied the temperature dependence of 14 observed Raman allowed phononic modes. These phonons couple strongly to this transition and one additional first order transition at approximately 170 K. In the high-temperature phase only 3 modes are observed, while below approximately 280 K all 14 modes become visible. Below approximately 170 K only 11 modes are observed. Our results shed light on the possible mechanism driving the transitions. ACL, VKT and GB acknowledge support by NSF DMR-1104884.

  2. Multidimensional IRT Models for Composite Scores

    ERIC Educational Resources Information Center

    Yen, Shu Jing; Walker, Leah

    2007-01-01

    Tests of English Language Proficiency are often designed such that each section of the test measures a single latent ability. For instance an English Proficiency Assessment might consist of sections measuring Speaking, Listening, and Reading ability. However, Overall English Proficiency and composite abilities are naturally multidimensional. This…

  3. Assessing the Impact of Faking on Binary Personality Measures: An IRT-Based Multiple-Group Factor Analytic Procedure

    ERIC Educational Resources Information Center

    Ferrando, Pere J.; Anguiano-Carrasco, Cristina

    2009-01-01

    This article proposes a model-based multiple-group procedure for assessing the impact of faking on personality measures and the scores derived from these measures. The assessment is at the item level and the base model, which is intended for binary items, can be parameterized both as an Item Response Theory (IRT) model and as an Item…

  4. IRT in the investigation of buildings and historic structures

    NASA Astrophysics Data System (ADS)

    Avdelidis, Nicolas P.; Moropoulou, Antonia

    2004-04-01

    Although, the efficiency of IRT (infrared thermography) as a NDT & E technique in the literature it is well documented, in the investigation of historic structures, where a restoration or conservation treatment can cause irreversible damage to the structure, it is considered to be of most importance. IRT is a non-destructive investigation technique that can be widely used due to the outstanding advantages that offers in a number of applications and specifically in the assessment of structural materials and techniques. In the present work, both IRT approaches, passive and active, were used, depending on the application, for the investigation of traditional-historical materials and structures. IRT was applied on restoration and traditional-historic materials and structures for the evaluation of conservation interventions (materials and techniques) concerning cleaning of architectural surfaces, restoration of masonries by repair mortars, as well as the disclosure of tesserae on plastered mosaic surfaces. For this reason, diagnostic studies on historical sites and structures took place. Wherever necessary, the emissivity values of the investigated materials were taken into account, after their determination in the laboratory on representative samples. Furthermore, in order to obtain useful information from the IRT surveys various properties (thermal, optical, physical) of the examined materials were taken into account. The outcome of this work provides strong evidence that IRT is an effective technique for the evaluation of historic buildings and sites.

  5. Measuring Anxiety in Visually-Impaired People: A Comparison between the Linear and the Nonlinear IRT Approaches

    ERIC Educational Resources Information Center

    Ferrando, Pere J.; Pallero, Rafael; Anguiano-Carrasco, Cristina

    2013-01-01

    The present study has two main interests. First, some pending issues about the psychometric properties of the CTAC (an anxiety questionnaire for blind and visually-impaired people) are assessed using item response theory (IRT). Second, the linear model is compared to the graded response model (GRM) in terms of measurement precision, sensitivity…

  6. [CII] Diffuse Emission Observed by IRTS

    NASA Astrophysics Data System (ADS)

    Shibai, Hiroshi; Okuda, Haruyuki; Nakagawa, Takao; Makiuti, Sin'itirou; Matsuhara, Hideo; Hiromoto, Norihisa; Okumura, Ken'ichi

    1996-12-01

    The [CII] 158 mu m line emission and the far-infrared continuum emission at 155 mu m were observed by the Far-Infrared Line Mapper (FILM) aboard the Infrared Telescope in Space (IRTS) with its high sensitivity and resolution. The observation was made along a great circle crossing the galactic plane at l = 50(deg) and 230(deg) . Two components were found in their intensity distributions. The first component concentrates on the galactic plane. It is prominent on the plane at l = 50(deg) , but is very faint at 230(deg) . The second component extends over at least 20(deg) in galactic latitude, and has nearly the same intensity at both crossing parts of the galactic plane. Therefore, the first one can be ascribed to emission from the galactic disk, and the second component to emission from the local interstellar gas. The intensity distribution of the [CII] line of the second component is similar to that of the HI 21 cm integrated intensity. This fact suggests that the local [CII] emission component arises in the HI 21 cm line emitting gas. From the ratio of the [CII] line luminosity to the hydrogen column density, the interstellar cooling rate of the HI gas is (5.6 +/- 2.6) times 10(-27) erg s(-1) /H-atom, corresponding to the cold neutral gas whose pressure is a few hundred cm(-3) K.

  7. Integrated Ray Tracing (IRT) simulation of SCOTS measurement of GMT fast steering mirror surface

    NASA Astrophysics Data System (ADS)

    Choi, Ji Nyeong; Ryu, Dongok; Kim, Sug-Whan; Graves, Logan; Su, Peng; Huang, Run; Kim, Dae Wook

    2015-09-01

    The Software Configurable Optical Testing System (SCOTS) is one of the newest testing methods for large mirror surfaces. The Integrated Ray Tracing (IRT) technique can be applicable to the SCOTS simulation by performing non-sequential ray tracing from the screen to the camera detector in the real scale. Therefore, the radiometry of distorted pattern images are numerically estimated by the IRT simulation module. In this study, we construct an IRT SCOTS simulation model for the Fast Steering Mirror Prototype (FSMP) surface of the Giant Magellan Telescope (GMT). GMT FSMP is an off-axis ellipsoidal concave mirror that is 1064 mm in diameter and has PV 3.1 mm in aspheric departure. The surface error requirement is less than 20 nm rms. The screen is modeled as an array of 1366 by 768 screen pixels of 0.227 mm in pitch size. The screen is considered as a Lambertian scattering surface. The screen and the camera are positioned around 4390 mm away from the mirror and separated by around 132 mm from each other. The light source are scanning lines and sinusoidal patterns generated by 616,050 rays per one screen pixel. Of the initially generated rays, 0.22 % are received by the camera's detector and contribute to form distorted pattern images. These images are converted to the slope and height maps of the mirror surface. The final result for the height difference between input surface and reconstructed surface was 14.14 nm rms. Additionally, the simulated mirror pattern image was compared with the real SCOTS test for the GMT FSMP. This study shows applicability of using the IRT model to SCOTS simulation with nanometer level numerical accuracy.

  8. Small helium-cooled infrared telescope experiment for Spacelab-2 (IRT)

    NASA Technical Reports Server (NTRS)

    Fazio, Giovanni G.

    1990-01-01

    The Infrared Telescope (IRT) experiment, flown on Spacelab-2, was used to make infrared measurements between 2 and 120 microns. The objectives were multidisciplinary in nature with astrophysical goals of mapping the diffuse cosmic emission and extended infrared sources and technical goals of measuring the induced Shuttle environment, studying properties of superfluid helium in space, and testing various infrared telescope system designs. Astrophysically, new data were obtained on the structure of the Galaxy at near-infrared wavelengths. A summary of the large scale diffuse near-infrared observations of the Galaxy by the IRT is presented, as well as a summary of the preliminary results obtained from this data on the structure of the galactic disk and bulge. The importance of combining CO and near-infrared maps of similar resolution to determine a 3-D model of galactic extinction is demonstrated. The IRT data are used, in conjunction with a proposed galactic model, to make preliminary measurements of the global scale parameters of the Galaxy. During the mission substantial amounts of data were obtained concerning the induced Shuttle environment. An experiment was also performed to measure spacecraft glow in the IR.

  9. Methodological issues regarding power of classical test theory (CTT) and item response theory (IRT)-based approaches for the comparison of patient-reported outcomes in two groups of patients - a simulation study

    PubMed Central

    2010-01-01

    Background Patients-Reported Outcomes (PRO) are increasingly used in clinical and epidemiological research. Two main types of analytical strategies can be found for these data: classical test theory (CTT) based on the observed scores and models coming from Item Response Theory (IRT). However, whether IRT or CTT would be the most appropriate method to analyse PRO data remains unknown. The statistical properties of CTT and IRT, regarding power and corresponding effect sizes, were compared. Methods Two-group cross-sectional studies were simulated for the comparison of PRO data using IRT or CTT-based analysis. For IRT, different scenarios were investigated according to whether items or person parameters were assumed to be known, to a certain extent for item parameters, from good to poor precision, or unknown and therefore had to be estimated. The powers obtained with IRT or CTT were compared and parameters having the strongest impact on them were identified. Results When person parameters were assumed to be unknown and items parameters to be either known or not, the power achieved using IRT or CTT were similar and always lower than the expected power using the well-known sample size formula for normally distributed endpoints. The number of items had a substantial impact on power for both methods. Conclusion Without any missing data, IRT and CTT seem to provide comparable power. The classical sample size formula for CTT seems to be adequate under some conditions but is not appropriate for IRT. In IRT, it seems important to take account of the number of items to obtain an accurate formula. PMID:20338031

  10. A Unified Approach to IRT Scale Linking and Scale Transformations. Research Report. RR-04-09

    ERIC Educational Resources Information Center

    von Davier, Matthias; von Davier, Alina A.

    2004-01-01

    This paper examines item response theory (IRT) scale transformations and IRT scale linking methods used in the Non-Equivalent Groups with Anchor Test (NEAT) design to equate two tests, X and Y. It proposes a unifying approach to the commonly used IRT linking methods: mean-mean, mean-var linking, concurrent calibration, Stocking and Lord and…

  11. Local Equating Using the Rasch Model, the OPLM, and the 2PL IRT Model--or--What Is It Anyway if the Model Captures Everything There Is to Know about the Test Takers?

    ERIC Educational Resources Information Center

    von Davier, Matthias; González B., Jorge; von Davier, Alina A.

    2013-01-01

    Local equating (LE) is based on Lord's criterion of equity. It defines a family of true transformations that aim at the ideal of equitable equating. van der Linden (this issue) offers a detailed discussion of common issues in observed-score equating relative to this local approach. By assuming an underlying item response theory model, one of…

  12. Extending LMS to Support IRT-Based Assessment Test Calibration

    NASA Astrophysics Data System (ADS)

    Fotaris, Panagiotis; Mastoras, Theodoros; Mavridis, Ioannis; Manitsaris, Athanasios

    Developing unambiguous and challenging assessment material for measuring educational attainment is a time-consuming, labor-intensive process. As a result Computer Aided Assessment (CAA) tools are becoming widely adopted in academic environments in an effort to improve the assessment quality and deliver reliable results of examinee performance. This paper introduces a methodological and architectural framework which embeds a CAA tool in a Learning Management System (LMS) so as to assist test developers in refining items to constitute assessment tests. An Item Response Theory (IRT) based analysis is applied to a dynamic assessment profile provided by the LMS. Test developers define a set of validity rules for the statistical indices given by the IRT analysis. By applying those rules, the LMS can detect items with various discrepancies which are then flagged for review of their content. Repeatedly executing the aforementioned procedure can improve the overall efficiency of the testing process.

  13. IRTs of the ABCs: children's letter name acquisition.

    PubMed

    Phillips, Beth M; Piasta, Shayne B; Anthony, Jason L; Lonigan, Christopher J; Francis, David J

    2012-08-01

    We examined the developmental sequence of letter name knowledge acquisition by children from 2 to five years of age. Data from 2 samples representing diverse regions, ethnicity, and socioeconomic backgrounds (ns = 1074 and 500) were analyzed using item response theory (IRT) and differential item functioning techniques. Results from factor analyses indicated that letter name knowledge represented a unidimensional skill; IRT results yielded significant differences between letters in both difficulty and discrimination. Results also indicated an approximate developmental sequence in letter name learning for the simplest and most challenging to learn letters--but with no clear sequence between these extremes. Findings also suggested that children were most likely to first learn their first initial. We discuss implications for assessment and instruction.

  14. Analyses of the IRT, Sofia intital LEU core performance.

    SciTech Connect

    Matos, J.; Hanan, N.; Apolstolov, T.; Belousov, S.; Nuclear Engineering Division; Bulgarian Academy Science

    2006-01-01

    The initial LEU (IRT-4M fuel assemblies, 19.75% {sup 235}U) core of the new IRT-Sofia research reactor of the Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Science, Sofia, Bulgaria is jointly analyzed with the RERTR Program at Argonne National Laboratory (ANL) to evaluate its performance and other important characteristics for safety analyses. The initial configuration using 16 fuel assemblies (four 8-tube and twelve 6-tube fuel assemblies) detailed power distributions and beam tubes flux performance for two critical core states corresponding to different control rods positioning, and different performance characteristics are compared. Results of calculations for two configurations at the beginning of the second operation cycle using 17 fuel assemblies (sixteen burned fuel assemblies (FA) and one fresh 6-tube FA) are presented. The results provide important and useful information for safety analyses and performance of the future reactor operation.

  15. The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range.

    PubMed

    Korshunova, Y O; Eide, D; Clark, W G; Guerinot, M L; Pakrasi, H B

    1999-05-01

    The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1 delta). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.

  16. Icing Research Tunnel (IRT) Force Measurement System (FMS)

    NASA Technical Reports Server (NTRS)

    Roberts, Paul W.

    2012-01-01

    An Electronics Engineer at the Glenn Research Center (GRC), requested the NASA Engineering and Safety Center (NESC) provide technical support for an evaluation of the existing force measurement system (FMS) at the GRC's Icing Research Tunnel (IRT) with the intent of developing conceptual designs to improve the tunnel's force measurement capability in order to better meet test customer needs. This report contains the outcome of the NESC technical review.

  17. What IRT Can and Cannot Do

    ERIC Educational Resources Information Center

    Glas, Cees A. W.

    2009-01-01

    This author states that, while the article by Gunter Maris and Timo Bechger ("On Interpreting the Model Parameters for the Three Parameter Logistic Model," this issue) is highly interesting, the interest is not so much in the practical implications, but rather in the issue of the meaning and role of statistical models in psychometrics and…

  18. The Infrared-Optical Telescope (IRT) of the Exist Observatory

    NASA Technical Reports Server (NTRS)

    Kutyrev, Alexander; Bloom, Joshua; Gehrels, Neil; Golisano, Craig; Gong, Quan; Grindlay, Jonathan; Moseley, Samuel; Woodgate, Bruce

    2010-01-01

    The IRT is a 1.1m visible and infrared passively cooled telescope, which can locate, identify and obtain spectra of GRB afterglows at redshifts up to z 20. It will also acquire optical-IR, imaging and spectroscopy of AGN and transients discovered by the EXIST (The Energetic X-ray Imaging Survey Telescope). The IRT imaging and spectroscopic capabilities cover a broad spectral range from 0.32.2m in four bands. The identical fields of view in the four instrument bands are each split in three subfields: imaging, objective prism slitless for the field and objective prism single object slit low resolution spectroscopy, and high resolution long slit on single object. This allows the instrument, to do simultaneous broadband photometry or spectroscopy of the same object over the full spectral range, thus greatly improving the efficiency of the observatory and its detection limits. A prompt follow up (within three minutes) of the transient discovered by the EXIST makes IRT a unique tool for detection and study of these events, which is particularly valuable at wavelengths unavailable to the ground based observatories.

  19. Psychometric properties for the Balanced Inventory of Desirable Responding: dichotomous versus polytomous conventional and IRT scoring.

    PubMed

    Vispoel, Walter P; Kim, Han Yi

    2014-09-01

    [Correction Notice: An Erratum for this article was reported in Vol 26(3) of Psychological Assessment (see record 2014-16017-001). The mean, standard deviation and alpha coefficient originally reported in Table 1 should be 74.317, 10.214 and .802, respectively. The validity coefficients in the last column of Table 4 are affected as well. Correcting this error did not change the substantive interpretations of the results, but did increase the mean, standard deviation, alpha coefficient, and validity coefficients reported for the Honesty subscale in the text and in Tables 1 and 4. The corrected versions of Tables 1 and Table 4 are shown in the erratum.] Item response theory (IRT) models were applied to dichotomous and polytomous scoring of the Self-Deceptive Enhancement and Impression Management subscales of the Balanced Inventory of Desirable Responding (Paulhus, 1991, 1999). Two dichotomous scoring methods reflecting exaggerated endorsement and exaggerated denial of socially desirable behaviors were examined. The 1- and 2-parameter logistic models (1PLM, 2PLM, respectively) were applied to dichotomous responses, and the partial credit model (PCM) and graded response model (GRM) were applied to polytomous responses. For both subscales, the 2PLM fit dichotomous responses better than did the 1PLM, and the GRM fit polytomous responses better than did the PCM. Polytomous GRM and raw scores for both subscales yielded higher test-retest and convergent validity coefficients than did PCM, 1PLM, 2PLM, and dichotomous raw scores. Information plots showed that the GRM provided consistently high measurement precision that was superior to that of all other IRT models over the full range of both construct continuums. Dichotomous scores reflecting exaggerated endorsement of socially desirable behaviors provided noticeably weak precision at low levels of the construct continuums, calling into question the use of such scores for detecting instances of "faking bad." Dichotomous

  20. REANALYSIS OF THE NEAR-INFRARED EXTRAGALACTIC BACKGROUND LIGHT BASED ON THE IRTS OBSERVATIONS

    SciTech Connect

    Matsumoto, T.; Kim, M. G.; Pyo, J.; Tsumura, K.

    2015-07-01

    We reanalyze data of the near-infrared background taken by IRTS using up-to-date observational results of zodiacal light (ZL), integrated star light, and diffuse Galactic light. We confirm the existence of residual isotropic emission, which is slightly lower but almost the same as previously reported. At wavelengths longer than 2 μm, the result is fairly consistent with the recent observation with AKARI. We also perform the same analysis using a different ZL model by Wright and detect residual isotropic emission that is slightly lower than that based on the original Kelsall model. Both models show residual isotropic emission that is significantly brighter than the integrated light of galaxies.

  1. Determination of IRT-2M fuel burnup by gamma spectrometry.

    PubMed

    Koleška, Michal; Viererbl, Ladislav; Marek, Milan; Ernest, Jaroslav; Šunka, Michal; Vinš, Miroslav

    2016-01-01

    A spectrometric system was developed for evaluating spent fuel in the LVR-15 research reactor, which employs highly enriched (36%) IRT-2M-type fuel. Such system allows the measurement of detailed fission product profiles. Within these measurements, nuclides such as (137)Cs, (134)Cs, (144)Ce, (106)Ru and (154)Eu may be detected in fuel assemblies with different cooling times varying between 1.67 and 7.53 years. Burnup calculations using the MCNPX Monte Carlo code data showed good agreement with measurements, though some discrepancies were observed in certain regions. These discrepancies are attributed to the evaluation of irradiation history, reactor regulation pattern and buildup schemes.

  2. Expression of Malus xiaojinensis IRT1 (MxIRT1) protein in transgenic yeast cells leads to degradation through autophagy in the presence of excessive iron.

    PubMed

    Li, Shuang; Zhang, Xi; Zhang, Xiu-Yue; Xiao, Wei; Berry, James O; Li, Peng; Jin, Si; Tan, Song; Zhang, Peng; Zhao, Wei-Zhong; Yin, Li-Ping

    2015-07-01

    Iron is essential for plants, but highly toxic when present in excess. Consequently, iron uptake by root transporters must be finely tuned to avoid excess uptake from soil under iron excess. The iron-regulated transporter of Malus xiaojinensis (MxIRT1), induced in roots under iron deficiency, is a highly effective iron(II) transporter. Here, we investigated how the presence of excessive iron leads to MxIRT1 degradation in yeast expressing this plant iron transporter protein. To determine the relationship between iron abundance and MxIRT1 degradation, relative levels of autophagy-related gene-8 (ATG8) mRNA and the active ATG8-phosphatidylethanolamine-conjugated (PE) protein were measured in wild-type yeast and the autophagic mutant strains atg1∆, atg5∆, atg7∆, ypt7∆ and tor1∆ under normal and excessive iron conditions. The data showed that the exposure of MxIRT1-eGFP-transformed wild-type and tor1∆ strains to excessive iron led to significantly increased levels of ATG8 transcript and ATG8-PE protein, which resulted in enhanced MxIRT1 degradation. Co-localization of mCherry-ATG8 and MxIRT1-eGFP provided evidence that these proteins interact during autophagy in yeast. While inhibition of autophagic initiation, autophagosome formation and vacuole fusion all decreased MxIRT1 degradation. PMSF inhibition of autophagy prevented degradation, leading to the accumulation of MxIRT1-containing vesicles in the vacuoles. MxIRT1-vesicles were sorted into autophagosomes for iron-induced degradation in yeast, whereas the endogenous iron(II) transporter Fet4 was degraded in an autophagy-independent manner. Moreover, immunoprecipitation showed that multimono-ubiquitins provided MxIRT1 with the ubiquitination signal. Together, three factors, iron excess, autophagy and mono-ubiquitination, affect the functional activity and stability of exogenous MxIRT1 in yeast, thereby preventing iron uptake via this root transporter.

  3. IRT-Stimulus Contingencies in Chained Schedules: Implications for the Concept of Conditioned Reinforcement

    ERIC Educational Resources Information Center

    Bejarano, Rafael; Hackenberg, Timothy D.

    2007-01-01

    Two experiments with pigeons investigated the effects of contingencies between interresponse times (IRTs) and the transitions between the components of 2- and 4-component chained schedules (Experiments 1 and 2, respectively). The probability of component transitions varied directly with the most recent (Lag 0) IRT in some experimental conditions…

  4. Investigation of IRT-Based Equating Methods in the Presence of Outlier Common Items

    ERIC Educational Resources Information Center

    Hu, Huiqin; Rogers, W. Todd; Vukmirovic, Zarko

    2008-01-01

    Common items with inconsistent b-parameter estimates may have a serious impact on item response theory (IRT)--based equating results. To find a better way to deal with the outlier common items with inconsistent b-parameters, the current study investigated the comparability of 10 variations of four IRT-based equating methods (i.e., concurrent…

  5. The Relationship between CTT and IRT Approaches in Analyzing Item Characteristics

    ERIC Educational Resources Information Center

    Abedalaziz, Nabeel; Leng, Chin Hai

    2013-01-01

    Most of the tests and inventories used by counseling psychologists have been developed using CTT; IRT derives from what is called latent trait theory. A number of important differences exist between CTT- versus IRT-based approaches to both test development and evaluation, as well as the process of scoring the response profiles of individual…

  6. IRT wireless interface for automatic irrigation scheduling of a center pivot system

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Infrared thermometers (IRTs) have been widely used in agricultural research as a method to measure canopy temperatures, an indicator of crop water stress. Although IRTs have proven to be reliable within the critical range for plant stress, they would be cumbersome for the grower to set up, maintain,...

  7. IRT Scale Linking Methods for Mixed-Format Tests. ACT Research Report Series 2004-5

    ERIC Educational Resources Information Center

    Kim, Seonghoon; Lee, Won-Chan

    2004-01-01

    Under item response theory (IRT), obtaining a common proficiency scale is required in many applications. Four IRT linking methods, including the mean/mean, mean/sigma, Haebara, and Stocking-Lord methods, have been developed and widely used to estimate linking coefficients (slope and intercept) for a linear transformation from one scale to…

  8. An Extension of Four IRT Linking Methods for Mixed-Format Tests

    ERIC Educational Resources Information Center

    Kim, Seonghoon; Lee, Won-Chan

    2006-01-01

    Under item response theory (IRT), linking proficiency scales from separate calibrations of multiple forms of a test to achieve a common scale is required in many applications. Four IRT linking methods including the mean/mean, mean/sigma, Haebara, and Stocking-Lord methods have been presented for use with single-format tests. This study extends the…

  9. Practical Issues in Estimating Classification Accuracy and Consistency with R Package cacIRT

    ERIC Educational Resources Information Center

    Lathrop, Quinn N.

    2015-01-01

    There are two main lines of research in estimating classification accuracy (CA) and classification consistency (CC) under Item Response Theory (IRT). The R package cacIRT provides computer implementations of both approaches in an accessible and unified framework. Even with available implementations, there remains decisions a researcher faces when…

  10. Induction of IRT1 by the nickel-induced iron-deficient response in Arabidopsis.

    PubMed

    Nishida, Sho; Aisu, Ayaka; Mizuno, Takafumi

    2012-03-01

    Excessive amounts of nickel (Ni) can be toxic for plants. Recently, we reported that IRT1, the primary iron (Fe) uptake transporter in roots, meditates excess Ni accumulation in Arabidopsis thaliana. We also found that Ni exposure increases IRT1 expression in roots, suggesting that Ni uptake is further induced by Ni stress. Here, we show that Ni exposure induces expression of not only IRT1, but also FRO2, a ferric reductase in the root epidermis, and FIT, a transcription factor regulating the expression of genes involved in Fe homeostasis including IRT1 and FRO2. This result suggests that Ni accumulation induces an Fe-deficient response and leads to the induction of IRT1. Our findings suggest that excess Ni causes Fe deficiency at the molecular level and induces Fe deficiency signaling in plant cells.

  11. The metal ion transporter IRT1 is necessary for iron homeostasis and efficient photosynthesis in Arabidopsis thaliana.

    PubMed

    Varotto, Claudio; Maiwald, Daniela; Pesaresi, Paolo; Jahns, Peter; Salamini, Francesco; Leister, Dario

    2002-09-01

    The mutants irt1-1 and irt1-2 of Arabidopsis thaliana were identified among a collection of T-DNA-tagged lines on the basis of a decrease in the effective quantum yield of photosystem II. The mutations responsible interfere with expression of IRT1, a nuclear gene that encodes the metal ion transporter IRT1. In irt1 mutants, photosensitivity and chlorophyll fluorescence parameters, as well as abundance and composition of the photosynthetic apparatus, are significantly altered. Additional effects of the mutation under greenhouse conditions, including chlorosis and a drastic reduction in growth rate and fertility, are compatible with a deficiency in iron transport. Propagation of irt1 plants on media supplemented with additional quantities of iron salts restores almost all aspects of wild-type behaviour. The irt2-1 mutant, which carries an En insertion in the highly homologous IRT2 gene of Arabidopsis thaliana, was identified by reverse genetics and shows no symptoms of iron deficiency. This, together with the finding that irt1-1 can be complemented by 35S::IRT1 but not by 35S::IRT2, demonstrates that, although the products of the two genes are closely related, only AtIRT1 is required for iron homeostasis under physiological conditions.

  12. Criticality calculations for the VR-1 reactor with IRT-3M-HEU fuel and IRT-4MLEU fuel.

    SciTech Connect

    Hanan, N. A.; Matos, J. E.

    2007-01-17

    At The request of the Czech Technical University in Prague, ANL has performed independent verification calculations using the MCNP Monte Carlo code for three core configurations of the VR-1 reactor: a current core configuration B1 with HEU (36%) IRT-3M fuel assemblies and planned core configurations C1 and C2 with LEU (19.7%) IRT-4M fuel assemblies. Details of these configurations were provided to ANL by CTU. For core configuration B1, criticality calculations were performed for two sets of control rod positions provided to ANL by CTU. For core configurations C1 and C2, criticality calculations were done for cases with all control rods at the top positions, all control rods at the bottom positions, and two critical states of the reactor for different control rod positions. In addition, sensitivity studies for variation of the {sup 235}U mass in each fuel assembly and variation of the fuel meat and cladding thicknesses in each of the fuel tubes were done for the C1 core configuration. Finally the reactivity worth of the individual control rods was calculated for the B1, C1, and C2 core configurations.

  13. Item Response Modeling with BILOG-MG and MULTILOG for Windows

    ERIC Educational Resources Information Center

    Rupp, Andre A.

    2003-01-01

    Item response theory (IRT) has become one of the most popular scoring frameworks for measurement data. IRT models are used frequently in computerized adaptive testing, cognitively diagnostic assessment, and test equating. This article reviews two of the most popular software packages for IRT model estimation, BILOG-MG (Zimowski, Muraki, Mislevy, &…

  14. An Introduction to Item Response Theory and Rasch Models for Speech-Language Pathologists

    ERIC Educational Resources Information Center

    Baylor, Carolyn; Hula, William; Donovan, Neila J.; Doyle, Patrick J.; Kendall, Diane; Yorkston, Kathryn

    2011-01-01

    Purpose: To present a primarily conceptual introduction to item response theory (IRT) and Rasch models for speech-language pathologists (SLPs). Method: This tutorial introduces SLPs to basic concepts and terminology related to IRT as well as the most common IRT models. The article then continues with an overview of how instruments are developed…

  15. 125Te NMR study of IrTe 2

    NASA Astrophysics Data System (ADS)

    Mizuno, Kiyoshi; Magishi, Ko-ichi; Shinonome, Yasuaki; Saito, Takahito; Koyama, Kuniyuki; Matsumoto, Nobuhiro; Nagata, Shoichi

    2002-03-01

    We have measured 125Te NMR of IrTe2 in order to elucidate the origin of the anomalous behaviors in electrical and magnetic properties around 270 K. In high-temperature region, the NMR spectrum exhibits a sharp line. On the other hand, in low-temperature region, the spectrum shifts to higher magnetic field and splits into three lines. Also, the nuclear spin-lattice relaxation rate, 1/T1, is proportional to the temperature in both temperature sides; Korringa-like behavior which is characteristic of a metallic state. From the T dependences of the spectrum and 1/T1 around 270 K, it is suggested that these anomalous behaviors may not be due to the charge density wave formation but be caused by a kind of lattice distortion at low temperature.

  16. Can IRT Solve the Missing Data Problem in Test Equating?

    PubMed Central

    Bolsinova, Maria; Maris, Gunter

    2016-01-01

    In this paper test equating is considered as a missing data problem. The unobserved responses of the reference population to the new test must be imputed to specify a new cutscore. The proportion of students from the reference population that would have failed the new exam and those having failed the reference exam are made approximately the same. We investigate whether item response theory (IRT) makes it possible to identify the distribution of these missing responses and the distribution of test scores from the observed data without parametric assumptions for the ability distribution. We show that while the score distribution is not fully identifiable, the uncertainty about the score distribution on the new test due to non-identifiability is very small. Moreover, ignoring the non-identifiability issue and assuming a normal distribution for ability may lead to bias in test equating, which we illustrate in simulated and empirical data examples. PMID:26779074

  17. IRT analysis on historic buildings: toward a controlled convection heating

    NASA Astrophysics Data System (ADS)

    Rosina, Elisabetta; Ludwig, Nicola; Redaelli, Veronica; Della Torre, Stefano; D'Ascola, Simona; Catalano, Michela; Faliva, Chiara

    2005-03-01

    Many applications of IRT on buildings require active approach. The solicitation has to be properly calculated, and the application has to take in account the optical characteristics of the surface and its thermal properties. In fact, non-homogeneities of the surface definitively affect the absorbance and reflectance of materials, as shown in literature. Therefore, in case of different colors like artistic paintings, dark stains and salts deposition a convection heating results more effective for IRT inspection, because it does not stimulate different localized absorption due to the colors. Using fan coil heaters, major difficulty is to obtain an even heating on the wall under inspection. The laboratory tests permitted to verify that the strength of rising warm air is higher than the one due to the heater ventilation. As a consequence, the effects of heating on the wall start from the upper part and decrease in a non-proportional way to the bottom. On the other side, thermal flux from a heater changes direction according to the geometry of the room, ambient conditions (initial temperature of the air, openings, etc), technical characteristics of the heater (power, speed of the fan, shape, etc) and its location (orientation, elevation, distance from the surface under investigation, etc). In addition, the increase of air temperature does not directly correspond to the increase of the surface temperature. The paper shows the characterization of a convective heating source, by laboratory measurements; to map the distribution of heat in time, the 14.000-26.000 kcal/h heater flux was measured following a 3D grid, by anemometers, probes, and IR Thermography.

  18. Expression of the IRT1 metal transporter is controlled by metals at the levels of transcript and protein accumulation.

    PubMed

    Connolly, Erin L; Fett, Janette P; Guerinot, Mary Lou

    2002-06-01

    Iron, an essential nutrient, is not readily available to plants because of its low solubility. In addition, iron is toxic in excess, catalyzing the formation of hydroxyl radicals that can damage cellular constituents. Consequently, plants must carefully regulate iron uptake so that iron homeostasis is maintained. The Arabidopsis IRT1 gene is the major transporter responsible for high-affinity iron uptake from the soil. Here, we show that the steady state level of IRT1 mRNA was induced within 24 h after transfer of plants to iron-deficient conditions, with protein levels peaking 72 h after transfer. IRT1 mRNA and protein were undetectable 12 h after plants were shifted back to iron-sufficient conditions. Overexpression of IRT1 did not confer dominant gain-of-function enhancement of metal uptake. Analysis of 35S-IRT1 transgenic plants revealed that although IRT1 mRNA was expressed constitutively in these plants, IRT1 protein was present only in the roots when iron is limiting. Under these conditions, plants that overexpressed IRT1 accumulated higher levels of cadmium and zinc than wild-type plants, indicating that IRT1 is responsible for the uptake of these metals and that IRT1 protein levels are indeed increased in these plants. Our results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.

  19. Hormone influence on the spatial regulation of IRT1 expression in iron-deficient Arabidopsis thaliana roots.

    PubMed

    Blum, Ailisa; Brumbarova, Tzvetina; Bauer, Petra; Ivanov, Rumen

    2014-04-10

    The IRON-REGULATED TRANSPORTER1 (IRT1) is the principal importer of soil iron in Arabidopsis thaliana. It has a complex intracellular trafficking behavior, including continuous cycling between plasma membrane and endosomes. SORTING NEXIN1 is required for the recycling of endosome-localized IRT1. In its absence, IRT1 is mistargeted for degradation, resulting in reduced plant iron-uptake efficiency. Consequently, IRT1 promoter activity gets limited to a specific portion of the root. We tested the influence of two hormones known to positively affect iron uptake on IRT1 spatial regulation. We found that ethylene treatment in wild-type background mimics the effects of the SNX-loss-of-function situation. Conversely, auxin splits the IRT1 expression zone and forces it toward the two extremities of the root. This shows that IRT1 expression along the root is modulated by ethylene-auxin interplay.

  20. A new network of faint calibration stars from the near infrared spectrometer (NIRS) on the IRTS

    NASA Technical Reports Server (NTRS)

    Freund, Minoru M.; Matsuura, Mikako; Murakami, Hiroshi; Cohen, Martin; Noda, Manabu; Matsuura, Shuji; Matsumoto, Toshio

    1997-01-01

    The point source extraction and calibration of the near infrared spectrometer (NIRS) onboard the Infrared Telescope in Space (IRTS) is described. About 7 percent of the sky was observed during a one month mission in the range of 1.4 micrometers to 4 micrometers. The accuracy of the spectral shape and absolute values of calibration stars provided by the NIRS/IRTS were validated.

  1. Knock-out of Arabidopsis metal transporter gene IRT1 results in iron deficiency accompanied by cell differentiation defects.

    PubMed

    Henriques, Rossana; Jásik, Ján; Klein, Markus; Martinoia, Enrico; Feller, Urs; Schell, Jeff; Pais, Maria S; Koncz, Csaba

    2002-11-01

    IRT1 and IRT2 are members of the Arabidopsis ZIP metal transporter family that are specifically induced by iron deprivation in roots and act as heterologous suppressors of yeast mutations inhibiting iron and zinc uptake. Although IRT1 and IRT2 are thought to perform redundant functions as root-specific metal transporters, insertional inactivation of the IRT1 gene alone results in typical symptoms of iron deficiency causing severe leaf chlorosis and lethality in soil. The irt1 mutation is characterized by specific developmental defects, including a drastic reduction of chloroplast thylakoid stacking into grana and lack of palisade parenchyma differentiation in leaves, reduced number of vascular bundles in stems, and irregular patterns of enlarged endodermal and cortex cells in roots. Pulse labeling with 59Fe through the root system shows that the irt1 mutation reduces iron accumulation in the shoots. Short-term labeling with 65Zn reveals no alteration in spatial distribution of zinc, but indicates a lower level of zinc accumulation. In comparison to wild-type, the irt1 mutant responds to iron and zinc deprivation by altered expression of certain zinc and iron transporter genes, which results in the activation of ZIP1 in shoots, reduction of ZIP2 transcript levels in roots, and enhanced expression of IRT2 in roots. These data support the conclusion that IRT1 is an essential metal transporter required for proper development and regulation of iron and zinc homeostasis in Arabidopsis.

  2. IRT1, an Arabidopsis transporter essential for iron uptake from the soil and for plant growth.

    PubMed

    Vert, Grégory; Grotz, Natasha; Dédaldéchamp, Fabienne; Gaymard, Frédéric; Guerinot, Mary Lou; Briat, Jean-François; Curie, Catherine

    2002-06-01

    Plants are the principal source of iron in most diets, yet iron availability often limits plant growth. In response to iron deficiency, Arabidopsis roots induce the expression of the divalent cation transporter IRT1. Here, we present genetic evidence that IRT1 is essential for the uptake of iron from the soil. An Arabidopsis knockout mutant in IRT1 is chlorotic and has a severe growth defect in soil, leading to death. This defect is rescued by the exogenous application of iron. The mutant plants do not take up iron and fail to accumulate other divalent cations in low-iron conditions. IRT1-green fluorescent protein fusion, transiently expressed in culture cells, localized to the plasma membrane. We also show, through promoter::beta-glucuronidase analysis and in situ hybridization, that IRT1 is expressed in the external cell layers of the root, specifically in response to iron starvation. These results clearly demonstrate that IRT1 is the major transporter responsible for high-affinity metal uptake under iron deficiency.

  3. Modeling Item-Position Effects within an IRT Framework

    ERIC Educational Resources Information Center

    Debeer, Dries; Janssen, Rianne

    2013-01-01

    Changing the order of items between alternate test forms to prevent copying and to enhance test security is a common practice in achievement testing. However, these changes in item order may affect item and test characteristics. Several procedures have been proposed for studying these item-order effects. The present study explores the use of…

  4. The Reliability and Precision of Total Scores and IRT Estimates as a Function of Polytomous IRT Parameters and Latent Trait Distribution

    ERIC Educational Resources Information Center

    Culpepper, Steven Andrew

    2013-01-01

    A classic topic in the fields of psychometrics and measurement has been the impact of the number of scale categories on test score reliability. This study builds on previous research by further articulating the relationship between item response theory (IRT) and classical test theory (CTT). Equations are presented for comparing the reliability and…

  5. The extracellular loop of IRT1 ZIP protein--the chosen one for zinc?

    PubMed

    Potocki, Slawomir; Valensin, Daniela; Camponeschi, Francesca; Kozlowski, Henryk

    2013-10-01

    Zinc complexes with the extracellular loop of IRT1 (iron-regulated transporter 1), a ZIP (ZRT/IRT - Related Protein) family protein from Arabidopsis thaliana, have been studied. This unstructured fragment is responsible for metal selectivity and is located between the II and III transmembrane domains of IRT1. Zinc complexes with the Ac-(95)MHVLPDSFEMLSSICLEENPWHK(117)-NH2 peptide (IRT1), revealed surprisingly high thermodynamic stability. Additionally, an N-terminal fragment of human/mouse ZIP 13 zinc transporter (MPGCPCPGCGMACPR-NH2, later called ZIP13+C), has been chosen for the thermodynamic stability comparison studies. The relative ZIP13+C stability has been shown using several Zn(2+) complexes with artificially arranged multi-cysteine sequences. An interesting coordination mode has been proposed for the IRT1-Zn(2+) complex, in which imidazoles from two histidines (His-96 and His-116), a cysteine thiolate (Cys-109) and one of a glutamic acid carboxyl group are involved. All data were collected using potentiometric, NMR and mass spectrometric methods.

  6. The Estimation of the IRT Reliability Coefficient and Its Lower and Upper Bounds, with Comparisons to CTT Reliability Statistics

    ERIC Educational Resources Information Center

    Kim, Seonghoon; Feldt, Leonard S.

    2010-01-01

    The primary purpose of this study is to investigate the mathematical characteristics of the test reliability coefficient rho[subscript XX'] as a function of item response theory (IRT) parameters and present the lower and upper bounds of the coefficient. Another purpose is to examine relative performances of the IRT reliability statistics and two…

  7. An Empirical Comparison of an Expert Systems Approach and an IRT Approach to Computer-Based Adaptive Mastery Testing.

    ERIC Educational Resources Information Center

    Luk, HingKwan

    This study examined whether an expert system approach involving intelligent selection of items (EXSPRT-I) is as efficient as item response theory (IRT) based three-parameter adaptive mastery testing (AMT) when there are enough subjects to estimate the three IRT item parameters for all items in the test and when subjects in the item parameter…

  8. Origin of the phase transition in IrTe2: structural modulation and local bonding instability

    SciTech Connect

    Cao, Huibo; Chakoumakos, Bryan C; Yan, Jiaqiang; Zhou, Haidong; Custelcean, Radu; Mandrus, D.; McGuire, Michael A; Singh, David J; Chen, Xin; Yang, Hui

    2013-01-01

    We used X-ray/neutron diffraction to determine the low temperature (LT) structure of IrTe2. A structural modulation was observed with a wavevector of k =(1/5, 0, 1/5) below Ts285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed the first principles calculations for high temperature (HT) and LT structures, which elucidate the nature of the phase transition and the LT structure. A local bonding instability associated with the Te 5p states is likely the origin of the structural phase transition in IrTe2.

  9. IRT1 degradation factor1, a ring E3 ubiquitin ligase, regulates the degradation of iron-regulated transporter1 in Arabidopsis.

    PubMed

    Shin, Lung-Jiun; Lo, Jing-Chi; Chen, Guan-Hong; Callis, Judy; Fu, Hongyong; Yeh, Kuo-Chen

    2013-08-01

    Fe is an essential micronutrient for plant growth and development; plants have developed sophisticated strategies to acquire ferric Fe from the soil. Nongraminaceous plants acquire Fe by a reduction-based mechanism, and graminaceous plants use a chelation-based mechanism. In Arabidopsis thaliana, which uses the reduction-based method, iron-regulated transporter1 (IRT1) functions as the most important transporter for ferrous Fe uptake. Rapid and constitutive degradation of IRT1 allows plants to quickly respond to changing conditions to maintain Fe homeostasis. IRT1 degradation involves ubiquitination. To identify the specific E3 ubiquitin ligases involved in IRT1 degradation, we screened a set of insertional mutants in RING-type E3 ligases and identified a mutant that showed delayed degradation of IRT1 and loss of IRT1-ubiquitin complexes. The corresponding gene was designated IRT1 degradation factor1 (IDF1). Evidence of direct interaction between IDF1 and IRT1 in the plasma membrane supported the role of IDF1 in IRT1 degradation. IRT1 accumulation was reduced when coexpressed with IDF1 in yeast or Xenopus laevis oocytes. IDF1 function was RING domain dependent. The idf1 mutants showed increased tolerance to Fe deficiency, resulting from increased IRT1 levels. This evidence indicates that IDF1 directly regulates IRT1 degradation through its RING-type E3 ligase activity.

  10. IRT1 DEGRADATION FACTOR1, a RING E3 Ubiquitin Ligase, Regulates the Degradation of IRON-REGULATED TRANSPORTER1 in Arabidopsis[C][W][OPEN

    PubMed Central

    Shin, Lung-Jiun; Lo, Jing-Chi; Chen, Guan-Hong; Callis, Judy; Fu, Hongyong; Yeh, Kuo-Chen

    2013-01-01

    Fe is an essential micronutrient for plant growth and development; plants have developed sophisticated strategies to acquire ferric Fe from the soil. Nongraminaceous plants acquire Fe by a reduction-based mechanism, and graminaceous plants use a chelation-based mechanism. In Arabidopsis thaliana, which uses the reduction-based method, IRON-REGULATED TRANSPORTER1 (IRT1) functions as the most important transporter for ferrous Fe uptake. Rapid and constitutive degradation of IRT1 allows plants to quickly respond to changing conditions to maintain Fe homeostasis. IRT1 degradation involves ubiquitination. To identify the specific E3 ubiquitin ligases involved in IRT1 degradation, we screened a set of insertional mutants in RING-type E3 ligases and identified a mutant that showed delayed degradation of IRT1 and loss of IRT1-ubiquitin complexes. The corresponding gene was designated IRT1 DEGRADATION FACTOR1 (IDF1). Evidence of direct interaction between IDF1 and IRT1 in the plasma membrane supported the role of IDF1 in IRT1 degradation. IRT1 accumulation was reduced when coexpressed with IDF1 in yeast or Xenopus laevis oocytes. IDF1 function was RING domain dependent. The idf1 mutants showed increased tolerance to Fe deficiency, resulting from increased IRT1 levels. This evidence indicates that IDF1 directly regulates IRT1 degradation through its RING-type E3 ligase activity. PMID:23995086

  11. A Note on the Item Information Function of the Four-Parameter Logistic Model

    ERIC Educational Resources Information Center

    Magis, David

    2013-01-01

    This article focuses on four-parameter logistic (4PL) model as an extension of the usual three-parameter logistic (3PL) model with an upper asymptote possibly different from 1. For a given item with fixed item parameters, Lord derived the value of the latent ability level that maximizes the item information function under the 3PL model. The…

  12. Using a Linear Regression Method to Detect Outliers in IRT Common Item Equating

    ERIC Educational Resources Information Center

    He, Yong; Cui, Zhongmin; Fang, Yu; Chen, Hanwei

    2013-01-01

    Common test items play an important role in equating alternate test forms under the common item nonequivalent groups design. When the item response theory (IRT) method is applied in equating, inconsistent item parameter estimates among common items can lead to large bias in equated scores. It is prudent to evaluate inconsistency in parameter…

  13. Robust Scale Transformation Methods in IRT True Score Equating under Common-Item Nonequivalent Groups Design

    ERIC Educational Resources Information Center

    He, Yong

    2013-01-01

    Common test items play an important role in equating multiple test forms under the common-item nonequivalent groups design. Inconsistent item parameter estimates among common items can lead to large bias in equated scores for IRT true score equating. Current methods extensively focus on detection and elimination of outlying common items, which…

  14. A Comparison of IRT Proficiency Estimation Methods under Adaptive Multistage Testing

    ERIC Educational Resources Information Center

    Kim, Sooyeon; Moses, Tim; Yoo, Hanwook

    2015-01-01

    This inquiry is an investigation of item response theory (IRT) proficiency estimators' accuracy under multistage testing (MST). We chose a two-stage MST design that includes four modules (one at Stage 1, three at Stage 2) and three difficulty paths (low, middle, high). We assembled various two-stage MST panels (i.e., forms) by manipulating two…

  15. Adjusting for Year to Year Rater Variation in IRT Linking--An Empirical Evaluation

    ERIC Educational Resources Information Center

    Yen, Shu Jing; Ochieng, Charles; Michaels, Hillary; Friedman, Greg

    2005-01-01

    The main purpose of this study was to illustrate a polytomous IRT-based linking procedure that adjusts for rater variations. Test scores from two administrations of a statewide reading assessment were used. An anchor set of Year 1 students' constructed responses were rescored by Year 2 raters. To adjust for year-to-year rater variation in IRT…

  16. The Effect of Year-to-Year Rater Variation on IRT Linking

    ERIC Educational Resources Information Center

    Yen, Shu Jing; Ochieng, Charles; Michaels, Hillary; Friedman, Greg

    2005-01-01

    Year-to-year rater variation may result in constructed response (CR) parameter changes, making CR items inappropriate to use in anchor sets for linking or equating. This study demonstrates how rater severity affected the writing and reading scores. Rater adjustments were made to statewide results using an item response theory (IRT) methodology…

  17. Comparison of IRT Likelihood Ratio Test and Logistic Regression DIF Detection Procedures

    ERIC Educational Resources Information Center

    Atar, Burcu; Kamata, Akihito

    2011-01-01

    The Type I error rates and the power of IRT likelihood ratio test and cumulative logit ordinal logistic regression procedures in detecting differential item functioning (DIF) for polytomously scored items were investigated in this Monte Carlo simulation study. For this purpose, 54 simulation conditions (combinations of 3 sample sizes, 2 sample…

  18. A Simulation Study on the Performance of Four Multidimensional IRT Scale Linking Methods

    ERIC Educational Resources Information Center

    Wei, Youhua

    2008-01-01

    Scale linking is the process of developing the connection between scales of two or more sets of parameter estimates obtained from separate test calibrations. It is the prerequisite for many applications of IRT, such as test equating and differential item functioning analysis. Unidimensional scale linking methods have been studied and applied…

  19. The Robustness of IRT-Based Vertical Scaling Methods to Violation of Unidimensionality

    ERIC Educational Resources Information Center

    Yin, Liqun

    2013-01-01

    In recent years, many states have adopted Item Response Theory (IRT) based vertically scaled tests due to their compelling features in a growth-based accountability context. However, selection of a practical and effective calibration/scaling method and proper understanding of issues with possible multidimensionality in the test data is critical to…

  20. Post-Hoc IRT Equating of Previously Administered English Tests for Comparison of Test Scores

    ERIC Educational Resources Information Center

    Saida, Chisato; Hattori, Tamaki

    2008-01-01

    Despite growing concerns about declining scholastic abilities of Japanese students throughout Japan prior to the implementation of the revised Courses of Study in 2002, little empirical evidence was available at that time to support this perceived decline in academic performance. This research describes post-hoc IRT equating of previously…

  1. IRT-LR-DIF with Estimation of the Focal-Group Density as an Empirical Histogram

    ERIC Educational Resources Information Center

    Woods, Carol M.

    2008-01-01

    Item response theory-likelihood ratio-differential item functioning (IRT-LR-DIF) is used to evaluate the degree to which items on a test or questionnaire have different measurement properties for one group of people versus another, irrespective of group-mean differences on the construct. Usually, the latent distribution is presumed normal for both…

  2. ResidPlots-2: Computer Software for IRT Graphical Residual Analyses

    ERIC Educational Resources Information Center

    Liang, Tie; Han, Kyung T.; Hambleton, Ronald K.

    2009-01-01

    This article discusses the ResidPlots-2, a computer software that provides a powerful tool for IRT graphical residual analyses. ResidPlots-2 consists of two components: a component for computing residual statistics and another component for communicating with users and for plotting the residual graphs. The features of the ResidPlots-2 software are…

  3. On Reporting IRT Ability Scores When the Test Is Not Unidimensional.

    ERIC Educational Resources Information Center

    Dirir, Mohamed A.; Sinclair, Norma

    The purpose of this study was to examine the effect of test dimensionality on the stability of examinee ability estimates and item response theory (IRT) based score reports. A simulation procedure based on W. F. Stout's Essential Unidimensionality was used to generate test data with one dominant trait for the whole test and three minor traits…

  4. Expected Values and Reliability of Number-Right Scores for IRT Calibrated Items.

    ERIC Educational Resources Information Center

    Dimitrov, Dimiter M.

    This paper provides analytic evaluations of expected (marginal) true-score measures for binary items given their item response theory (IRT) calibration. Under the assumption of normal trait distributions, marginalized true scores, error variance, true score variance, and reliability for norm-referenced and criterion-references interpretations are…

  5. A Comparison of Alternative Models for Testlets

    ERIC Educational Resources Information Center

    Li, Yanmei; Bolt, Daniel M.; Fu, Jianbin

    2006-01-01

    When tests are made up of testlets, standard item response theory (IRT) models are often not appropriate due to the local dependence present among items within a common testlet. A testlet-based IRT model has recently been developed to model examinees' responses under such conditions (Bradlow, Wainer, & Wang, 1999). The Bradlow, Wainer, and…

  6. Assessing Fit of Unidimensional Graded Response Models Using Bayesian Methods

    ERIC Educational Resources Information Center

    Zhu, Xiaowen; Stone, Clement A.

    2011-01-01

    The posterior predictive model checking method is a flexible Bayesian model-checking tool and has recently been used to assess fit of dichotomous IRT models. This paper extended previous research to polytomous IRT models. A simulation study was conducted to explore the performance of posterior predictive model checking in evaluating different…

  7. An Investigation of Goodness of Model Data Fit

    ERIC Educational Resources Information Center

    Onder, Ismail

    2007-01-01

    IRT models' advantages can only be realized when the model fits the data set of interest. Therefore, this study aimed to investigate which IRT model will provide the best fit to the data obtained from OZDEBYR OSS 2004 D-II Exam Science Test. In goodness-of-fit analysis, first the model assumptions and then the expected model features were checked.…

  8. Posterior Predictive Assessment of Item Response Theory Models

    ERIC Educational Resources Information Center

    Sinharay, Sandip; Johnson, Matthew S.; Stern, Hal S.

    2006-01-01

    Model checking in item response theory (IRT) is an underdeveloped area. There is no universally accepted tool for checking IRT models. The posterior predictive model-checking method is a popular Bayesian model-checking tool because it has intuitive appeal, is simple to apply, has a strong theoretical basis, and can provide graphical or numerical…

  9. Surface phases of the transition-metal dichalcogenide IrT e2

    NASA Astrophysics Data System (ADS)

    Chen, Chen; Kim, Jisun; Yang, Yifan; Cao, Guixin; Jin, Rongying; Plummer, E. W.

    2017-03-01

    Transition-metal dichalcogenide IrT e2 has attracted attention because of its striped lattice, charge ordering, and superconductivity. We have investigated the surface structure of IrT e2 , using low-energy electron diffraction and scanning tunneling microscopy. A complex striped lattice modulation as a function of temperature is observed, which shows hysteresis between cooling and warming. While the bulk 5 × 1 and 8 × 1 phases appear at high temperatures, the surface ground state has the 6 × 1 phase, not seen in the bulk, and the surface transition temperatures are distinct from the bulk. The broken symmetry at the surface creates a quite different phase diagram, with the coexistence of several periodicities resembling devil's staircase behavior.

  10. Phase transition in IrTe2 induced by spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Koley, S.

    2016-12-01

    IrTe2 has been renewed as an interesting system showing competing phenomenon between a questionable density-wave transition near 270 K followed by superconductivity with doping of high atomic number materials. Higher atomic numbers of Te and Ir supports strong spin-orbital coupling in this system. Using dynamical mean field theory with LDA band structure I have introduced Rashba spin orbit coupling in this system to get the interpretation for anomalous resistivity and related transition in this system. While no considerable changes are observed in DMFT results of Ir-5d band other than orbital selective pseudogap 'pinned' to Fermi level, Te-p band shows a van Hove singularity at the Fermi level except low temperature. Finally I discuss the implications of these results in theoretical understanding of ordering in IrTe2.

  11. Mirnov Coil Analysis by Singular Value Decomposition Method in IR-T1 Tokamak

    NASA Astrophysics Data System (ADS)

    Salemi, Mohammad K.; Saadat, Shervin; Ghoranneviss, Mahmoud; Tabadar, Alireza

    2010-10-01

    The spatial and temporal structures of magnetic signal in the tokamak is analyzed using recently developed singular value decomposition (SVD) technique to determine the structure of current perturbation as the discharge progresses. In this work we use SVD technique for that purpose in IR-T1 tokamak.ootnotetextC. Nardonet, ``Multichannel Fluctuation Data Analysis By The Singular Value Decomposition Method Application To MHD Modes In Jet,'' Plasma Physics & Controlled Fusion, V. 34, No. 9, 1992, 1447-1465

  12. New tests of the common calibration context for ISO, IRTS, and MSX

    NASA Technical Reports Server (NTRS)

    Cohen, Martin

    1997-01-01

    The work carried out in order to test, verify and validate the accuracy of the calibration spectra provided to the Infrared Space Observatory (ISO), to the Infrared Telescope in Space (IRTS) and to the Midcourse Space Experiment (MSX) for external calibration support of instruments, is reviewed. The techniques, used to vindicate the accuracy of the absolute spectra, are discussed. The work planned for comparing far infrared spectra of Mars and some of the bright stellar calibrators with long wavelength spectrometer data are summarized.

  13. An Aggregate IRT Procedure for Exploratory Factor Analysis

    ERIC Educational Resources Information Center

    Camilli, Gregory; Fox, Jean-Paul

    2015-01-01

    An aggregation strategy is proposed to potentially address practical limitation related to computing resources for two-level multidimensional item response theory (MIRT) models with large data sets. The aggregate model is derived by integration of the normal ogive model, and an adaptation of the stochastic approximation expectation maximization…

  14. Dynamic IRT for the frescoes assessment: the study case of Danza Macabra in Clusone (Italy)

    NASA Astrophysics Data System (ADS)

    Ludwig, Nicola; Rosina, Elisabetta

    2005-03-01

    IRT technique applications for the detection of the plasters defects in historic buildings are widely documented by scientific literature. Previous studies demonstrated the advantages of tomographic techniques to obtain quantitative results by IRT. With a quantitative approach, the dynamic measures of IRT, versus time and maximum value of thermal contrast, allows to locate the delamination and calculate its volume inside the thickness of the plaster. Nevertheless, effects are not prominent if compared with the ones caused by the interaction between surface and irradiation. Moreover these effects are lower than the noise due to the approximation of the spectral coefficient value. Authors already showed that the multispectral evaluation of the reflectance coefficients, in the range of visible and near IR, contributes to a proper evaluation of the thermograms shot on surfaces affected by chromatic alterations. In the study case, the evolution of the surface temperature in time allows to quantify the effects of spectral absorption (absorbance) in the thermograms. By comparing the thermograms to the maps of damages and intervention, it has been possible to correlate the materials and its state of conservation to the evolution of the thermal profile corresponding to each analyzed area.

  15. Results and Conclusions from the NASA Isokinetic Total Water Content Probe 2009 IRT Test

    NASA Technical Reports Server (NTRS)

    Reehorst, Andrew; Brinker, David

    2010-01-01

    The NASA Glenn Research Center has developed and tested a Total Water Content Isokinetic Sampling Probe. Since, by its nature, it is not sensitive to cloud water particle phase nor size, it is particularly attractive to support super-cooled large droplet and high ice water content aircraft icing studies. The instrument comprises the Sampling Probe, Sample Flow Control, and Water Vapor Measurement subsystems. Results and conclusions are presented from probe tests in the NASA Glenn Icing Research Tunnel (IRT) during January and February 2009. The use of reference probe heat and the control of air pressure in the water vapor measurement subsystem are discussed. Several run-time error sources were found to produce identifiable signatures that are presented and discussed. Some of the differences between measured Isokinetic Total Water Content Probe and IRT calibration seems to be caused by tunnel humidification and moisture/ice crystal blow around. Droplet size, airspeed, and liquid water content effects also appear to be present in the IRT calibration. Based upon test results, the authors provide recommendations for future Isokinetic Total Water Content Probe development.

  16. Development of an IRT-based Short Form to Assess Applied Cognitive Function in Outpatient Rehabilitation

    PubMed Central

    McDonough, Christine M.; Ni, Pengsheng; Coster, Wendy J.; Haley, Stephen M.; Jette, Alan M.

    2015-01-01

    Objective Item response theory (IRT) and computerized adaptive testing (CAT) methods allow the development of a large calibrated item bank from which different subsets of questions can be selected for administration and scored on a common scale. Our objective was to develop an outpatient rehabilitation self-report short form for the Activity Measure for Post-Acute Care Applied Cognition item bank. Design Using data from a convenience sample of 235 rehabilitation outpatients, item content and IRT-based test information function parameters were employed in item selection. Internal consistency reliability, Intraclass Correlation Coefficient (ICC), and percent at the lowest (floor) and highest (ceiling) scores were evaluated for the short form and full item bank. Results A 15-item short form was developed. The internal consistency of the short form was 0.86. The ICC3,1 for the short form and item bank was 0.97 (95% CI: 0.94, 0.98). No floor effects were noted, and ceiling effects were 27.66 % (short form) and 26.38% (full item bank). Conclusions The Applied Cognition outpatient short form demonstrated acceptable psychometric properties and provides a bridge to IRT-based measurement for settings where point of care computing is not available. PMID:26135369

  17. Goodness of Model-Data Fit and Invariant Measurement

    ERIC Educational Resources Information Center

    Engelhard, George, Jr.; Perkins, Aminah

    2013-01-01

    In this commentary, Englehard and Perkins remark that Maydeu-Olivares has presented a framework for evaluating the goodness of model-data fit for item response theory (IRT) models and correctly points out that overall goodness-of-fit evaluations of IRT models and data are not generally explored within most applications in educational and…

  18. Estimating the Nominal Response Model under Nonnormal Conditions

    ERIC Educational Resources Information Center

    Preston, Kathleen Suzanne Johnson; Reise, Steven Paul

    2014-01-01

    The nominal response model (NRM), a much understudied polytomous item response theory (IRT) model, provides researchers the unique opportunity to evaluate within-item category distinctions. Polytomous IRT models, such as the NRM, are frequently applied to psychological assessments representing constructs that are unlikely to be normally…

  19. An NCME Instructional Module on Item-Fit Statistics for Item Response Theory Models

    ERIC Educational Resources Information Center

    Ames, Allison J.; Penfield, Randall D.

    2015-01-01

    Drawing valid inferences from item response theory (IRT) models is contingent upon a good fit of the data to the model. Violations of model-data fit have numerous consequences, limiting the usefulness and applicability of the model. This instructional module provides an overview of methods used for evaluating the fit of IRT models. Upon completing…

  20. Multilevel IRT Using Dichotomous and Polytomous Response Data. Research Report.

    ERIC Educational Resources Information Center

    Fox, Jean-Paul

    A structural multilevel model is presented in which some of the variables cannot be observed directly but are measured using tests or questionnaires. Observed dichotomous or ordinal politicos response data serve to measure the latent variables using an item response theory model. The latent variables can be defined at any level of the multilevel…

  1. Invariance Properties for General Diagnostic Classification Models

    ERIC Educational Resources Information Center

    Bradshaw, Laine P.; Madison, Matthew J.

    2016-01-01

    In item response theory (IRT), the invariance property states that item parameter estimates are independent of the examinee sample, and examinee ability estimates are independent of the test items. While this property has long been established and understood by the measurement community for IRT models, the same cannot be said for diagnostic…

  2. A Comparison of General Diagnostic Models (GDM) and Bayesian Networks Using a Middle School Mathematics Test

    ERIC Educational Resources Information Center

    Wu, Haiyan

    2013-01-01

    General diagnostic models (GDMs) and Bayesian networks are mathematical frameworks that cover a wide variety of psychometric models. Both extend latent class models, and while GDMs also extend item response theory (IRT) models, Bayesian networks can be parameterized using discretized IRT. The purpose of this study is to examine similarities and…

  3. Comparing the Fit of Item Response Theory and Factor Analysis Models

    ERIC Educational Resources Information Center

    Maydeu-Olivares, Alberto; Cai, Li; Hernandez, Adolfo

    2011-01-01

    Linear factor analysis (FA) models can be reliably tested using test statistics based on residual covariances. We show that the same statistics can be used to reliably test the fit of item response theory (IRT) models for ordinal data (under some conditions). Hence, the fit of an FA model and of an IRT model to the same data set can now be…

  4. A Primer on the 2- and 3-Parameter Item Response Theory Models.

    ERIC Educational Resources Information Center

    Thornton, Artist

    Item response theory (IRT) is a useful and effective tool for item response measurement if used in the proper context. This paper discusses the sets of assumptions under which responses can be modeled while exploring the framework of the IRT models relative to response testing. The one parameter model, or one parameter logistic model, is perhaps…

  5. Extended Mixed-Efects Item Response Models with the MH-RM Algorithm

    ERIC Educational Resources Information Center

    Chalmers, R. Philip

    2015-01-01

    A mixed-effects item response theory (IRT) model is presented as a logical extension of the generalized linear mixed-effects modeling approach to formulating explanatory IRT models. Fixed and random coefficients in the extended model are estimated using a Metropolis-Hastings Robbins-Monro (MH-RM) stochastic imputation algorithm to accommodate for…

  6. The Effect of Differential Motivation on IRT Linking

    ERIC Educational Resources Information Center

    Mittelhaëuser, Marie-Anne; Béguin, Anton A.; Sijtsma, Klaas

    2015-01-01

    The purpose of this study was to investigate whether simulated differential motivation between the stakes for operational tests and anchor items produces an invalid linking result if the Rasch model is used to link the operational tests. This was done for an external anchor design and a variation of a pretest design. The study also investigated…

  7. An uncleaved signal peptide directs the Malus xiaojinensis iron transporter protein Mx IRT1 into the ER for the PM secretory pathway.

    PubMed

    Zhang, Peng; Tan, Song; Berry, James O; Li, Peng; Ren, Na; Li, Shuang; Yang, Guang; Wang, Wei-Bing; Qi, Xiao-Ting; Yin, Li-Ping

    2014-11-07

    Malus xiaojinensis iron-regulated transporter 1 (Mx IRT1) is a highly effective inducible iron transporter in the iron efficient plant Malus xiaojinensis. As a multi-pass integral plasma membrane (PM) protein, Mx IRT1 is predicted to consist of eight transmembrane domains, with a putative N-terminal signal peptide (SP) of 1-29 amino acids. To explore the role of the putative SP, constructs expressing Mx IRT1 (with an intact SP) and Mx DsIRT1 (with a deleted SP) were prepared for expression in Arabidopsis and in yeast. Mx IRT1 could rescue the iron-deficiency phenotype of an Arabidopsis irt1 mutant, and complement the iron-limited growth defect of the yeast mutant DEY 1453 (fet3fet4). Furthermore, fluorescence analysis indicated that a chimeric Mx IRT1-eGFP (enhanced Green Fluorescent Protein) construct was translocated into the ER (Endoplasmic reticulum) for the PM sorting pathway. In contrast, the SP-deleted Mx DsIRT1 could not rescue either of the mutant phenotypes, nor direct transport of the GFP signal into the ER. Interestingly, immunoblot analysis indicated that the SP was not cleaved from the mature protein following transport into the ER. Taken together, data presented here provides strong evidence that an uncleaved SP determines ER-targeting of Mx IRT1 during the initial sorting stage, thereby enabling the subsequent transport and integration of this protein into the PM for its crucial role in iron uptake.

  8. An Uncleaved Signal Peptide Directs the Malus xiaojinensis Iron Transporter Protein Mx IRT1 into the ER for the PM Secretory Pathway

    PubMed Central

    Zhang, Peng; Tan, Song; Berry, James O.; Li, Peng; Ren, Na; Li, Shuang; Yang, Guang; Wang, Wei-Bing; Qi, Xiao-Ting; Yin, Li-Ping

    2014-01-01

    Malus xiaojinensis iron-regulated transporter 1 (Mx IRT1) is a highly effective inducible iron transporter in the iron efficient plant Malus xiaojinensis. As a multi-pass integral plasma membrane (PM) protein, Mx IRT1 is predicted to consist of eight transmembrane domains, with a putative N-terminal signal peptide (SP) of 1–29 amino acids. To explore the role of the putative SP, constructs expressing Mx IRT1 (with an intact SP) and Mx DsIRT1 (with a deleted SP) were prepared for expression in Arabidopsis and in yeast. Mx IRT1 could rescue the iron-deficiency phenotype of an Arabidopsis irt1 mutant, and complement the iron-limited growth defect of the yeast mutant DEY 1453 (fet3fet4). Furthermore, fluorescence analysis indicated that a chimeric Mx IRT1-eGFP (enhanced Green Fluorescent Protein) construct was translocated into the ER (Endoplasmic reticulum) for the PM sorting pathway. In contrast, the SP-deleted Mx DsIRT1 could not rescue either of the mutant phenotypes, nor direct transport of the GFP signal into the ER. Interestingly, immunoblot analysis indicated that the SP was not cleaved from the mature protein following transport into the ER. Taken together, data presented here provides strong evidence that an uncleaved SP determines ER-targeting of Mx IRT1 during the initial sorting stage, thereby enabling the subsequent transport and integration of this protein into the PM for its crucial role in iron uptake. PMID:25387073

  9. Gibberellic acid alleviates cadmium toxicity by reducing nitric oxide accumulation and expression of IRT1 in Arabidopsis thaliana.

    PubMed

    Zhu, Xiao Fang; Jiang, Tao; Wang, Zhi Wei; Lei, Gui Jie; Shi, Yuan Zhi; Li, Gui Xin; Zheng, Shao Jian

    2012-11-15

    Gibberellic acid (GA) is involved in not only plant growth and development but also plant responses to abiotic stresses. Here it was found that treating the plants with GA concentrations from 0.1 to 5 μM for 24 h had no obvious effect on root elongation in the absence of cadmium (Cd), whereas in the presence of Cd2+, GA at 5 μM improved root growth, reduced Cd content and lipid peroxidation in the roots, indicating that GA can partially alleviate Cd toxicity. Cd2+ increased nitric oxide (NO) accumulation in the roots, but GA remarkably reduced it, and suppressed the up-regulation of the expression of IRT1. In contrary, the beneficial effect of GA on alleviating Cd toxicity was not observed in an IRT1 knock-out mutant irt1, suggesting the involvement of IRT1 in Cd2+ absorption. Furthermore, the GA-induced reduction of NO and Cd content can also be partially reversed by the application of a NO donor (S-nitrosoglutathione [GSNO]). Taken all these together, the results showed that GA-alleviated Cd toxicity is mediated through the reduction of the Cd-dependent NO accumulation and expression of Cd2+ uptake related gene-IRT1 in Arabidopsis.

  10. An IRT Analysis of the Symptoms of Major Depressive Disorder.

    PubMed

    Emmert-Aronson, Benjamin O; Brown, Timothy A

    2015-06-01

    This study examines the psychometric properties of a major depressive episode using a large sample (N = 2,907) of outpatients with mood and anxiety disorders. A two-parameter logistic model yielded item threshold and discrimination parameters. A two-group confirmatory factor analysis was used to evaluate gender bias. Item thresholds fell along a continuum with the core features of depressed mood and anhedonia, along with fatigue, endorsed at lower levels of depression, and change in appetite and suicidal ideation endorsed at more severe levels. Item discriminations were highest for depressed mood and anhedonia, and lowest for change in appetite and suicidal ideation. The data indicate that the symptoms of depression assess a range of severity, with varying precision in discriminating depression. No gender differences were observed. Three exploratory symptom sets were compared with the full symptom set for depression, offering quantitative evidence that can be used to modify the psychiatric classification system.

  11. How Often Is the Misfit of Item Response Theory Models Practically Significant?

    ERIC Educational Resources Information Center

    Sinharay, Sandip; Haberman, Shelby J.

    2014-01-01

    Standard 3.9 of the Standards for Educational and Psychological Testing ([, 1999]) demands evidence of model fit when item response theory (IRT) models are employed to data from tests. Hambleton and Han ([Hambleton, R. K., 2005]) and Sinharay ([Sinharay, S., 2005]) recommended the assessment of practical significance of misfit of IRT models, but…

  12. Maximin Calibration Designs for the Nominal Response Model: An Empirical Evaluation

    ERIC Educational Resources Information Center

    Passos, Valeria Lima; Berger, Martijn P. F.

    2004-01-01

    The problem of finding optimal calibration designs for dichotomous item response theory (IRT) models has been extensively studied in the literature. In this study, this problem will be extended to polytomous IRT models. Focus is given to items described by the nominal response model (NRM). The optimizations objective is to minimize the generalized…

  13. Fitting a Mixture Item Response Theory Model to Personality Questionnaire Data: Characterizing Latent Classes and Investigating Possibilities for Improving Prediction

    ERIC Educational Resources Information Center

    Maij-de Meij, Annette M.; Kelderman, Henk; van der Flier, Henk

    2008-01-01

    Mixture item response theory (IRT) models aid the interpretation of response behavior on personality tests and may provide possibilities for improving prediction. Heterogeneity in the population is modeled by identifying homogeneous subgroups that conform to different measurement models. In this study, mixture IRT models were applied to the…

  14. Investigating latent constructs with item response models: a MATLAB IRTm toolbox.

    PubMed

    Braeken, Johan; Tuerlinckx, Francis

    2009-11-01

    Item response theory (IRT) models are the central tools in modern measurement and advanced psychometrics. We offer a MATLAB IRT modeling (IRTm) toolbox that is freely available and that follows an explicit design matrix approach, giving the end user control and flexibility in building a model that goes beyond standard models, such as the Rasch model (Rasch, 1960) and the two-parameter logistic model. As such, IRTm allows for a large variety of unidimensional IRT models for binary responses, the incorporation of additional person and item information, and deviations from common model assumptions. An exclusive key feature of the toolbox is the inclusion of copula IRT models to handle local item dependencies. Two appendixes for this report, containing example code and information on the general copula IRT in IRTm, may be downloaded from brm.psychonomic-journals.org/content/supplemental.

  15. Transcription of the mating-type-regulated lncRNA IRT1 is governed by TORC1 and PKA.

    PubMed

    Moretto, Fabien; van Werven, Folkert J

    2016-08-12

    Cell fate decisions are controlled by multiple cell-intrinsic and -extrinsic factors. In budding yeast, the decision to enter gametogenesis or sporulation is dictated by nutrient availability and mating type. Recently, we showed that in diploid cells harbouring opposite mating types (MATa and MATα), the protein kinase A (PKA) and target of rapamycin complex I (TORC1) signalling pathways integrate at the promoter of the master regulatory transcription factor IME1 to control sporulation via nutrient availability (Weidberg, et al. 2016). In cells with a single mating type (MATa or MATα), however, IME1 is repressed by transcription through the IME1 promoter of a long non-coding RNA called IRT1, which prevents this cell type from undergoing sporulation. Here, we investigated the role of nutrient signalling in mating-type control of IME1. We find that expression of IRT1, like IME1 itself, depends on nutrient availability and the activities of PKA and TORC1. IRT1 transcription is repressed when nutrients are ample and TORC1 and PKA are active. In contrast, inhibition of PKA and TORC1 is sufficient to recruit Rme1 to the IRT1 promoter and induce IRT1-mediated repression of IME1. Finally, we provide evidence that IRT1 and IME1 are co-repressed by the Tup1-Cyc8 complex when nutrients are ample. Thus, in cells with a single mating-type nutrient availability regulates mating-type repression of IME1 and sporulation. Our results indicate that there is a hierarchy between nutrient and mating-type signals in controlling the decision to enter sporulation.

  16. DIF Testing for Ordinal Items with Poly-SIBTEST, the Mantel and GMH Tests, and IRT-LR-DIF when the Latent Distribution Is Nonnormal for Both Groups

    ERIC Educational Resources Information Center

    Woods, Carol M.

    2011-01-01

    Differential item functioning (DIF) occurs when an item on a test, questionnaire, or interview has different measurement properties for one group of people versus another. One way to test items with ordinal response scales for DIF is likelihood ratio (LR) testing using item response theory (IRT), or IRT-LR-DIF. Despite the various advantages of…

  17. On the Use of Covariates in a Latent Class Signal Detection Model, with Applications to Constructed Response Scoring

    ERIC Educational Resources Information Center

    Wang, Zijian Gerald

    2012-01-01

    A latent class signal detection (SDT) model was recently introduced as an alternative to traditional item response theory (IRT) methods in the analysis of constructed response data. This class of models can be represented as restricted latent class models and differ from the IRT approach in the way the latent construct is conceptualized. One…

  18. Electrical anisotropy and coexistence of structural transitions and superconductivity in IrT e2

    NASA Astrophysics Data System (ADS)

    Cao, Guixin; Xie, Weiwei; Phelan, W. Adam; DiTusa, J. F.; Jin, Rongying

    2017-01-01

    We report experimental investigations of the electrical transport, magnetic, and thermodynamic properties of IrT e2 single crystals. The resistivity, magnetization, and specific heat display anomalies at TS 1≈283 K ,TS 2≈167 K , and Tc≈2.5 K , corresponding to two structural and one superconducting phase transitions, respectively, demonstrating the coexistence of all of these transitions in high-quality stoichiometric samples. While there is little magnetic anisotropy, a large a b -plane (ρab) and c -axis (ρc) electrical resistivity ratio (ρc/ρab≈730 at T =4 K ) is observed. This two-dimensional (2D) electronic character is further reflected in the disparate temperature dependences of ρab and ρc, with ρab exhibiting a Fermi-liquid-like T2 dependence below ˜25 K , while ρc deviates significantly from this standard metallic behavior. In contrast, the magnetization is almost isotropic and negative over a wide temperature range. This can be explained by larger diamagnetism induced by electronic structure reconstruction as probed by the Hall effect and smaller positive contribution from itinerant electrons due to a low density of states (DOS) at the Fermi level. A small electronic specific heat coefficient with γ ≈1.8 mJ /mol K2 confirms this assertion. This implies that IrT e2 is a weakly coupled superconductor. The connection between the superconductivity and the two structural transitions is discussed.

  19. Probing IrTe2 crystal symmetry by polarized Raman scattering

    NASA Astrophysics Data System (ADS)

    Lazarević, N.; Bozin, E. S.; Šćepanović, M.; Opačić, M.; Lei, Hechang; Petrovic, C.; Popović, Z. V.

    2014-06-01

    Polarized Raman scattering measurements on IrTe2 single crystals carried out over the 15-640 K temperature range, and across the structural phase transition, reveal different insights regarding the crystal symmetry. In the high temperature regime three Raman active modes are observed at all of the studied temperatures above the structural phase transition, rather than two as predicted by the factor group analysis for the assumed P3¯m1 symmetry. This indicates that the actual symmetry of the high temperature phase is lower than previously thought. The observation of an additional Eg mode at high temperature can be explained by doubling of the original trigonal unit cell along the c axis and within the P3¯c1 symmetry. In the low temperature regime (below 245 K) the other Raman modes appear as a consequence of the symmetry lowering phase transition and the corresponding increase of the primitive cell. All of the modes observed below the phase transition temperature can be assigned within the monoclinic crystal symmetry. The temperature dependence of the Raman active phonons in both phases is mainly driven by anharmonicity effects. The results call for reconsideration of the crystallographic phases of IrTe2.

  20. Visualizing anisotropic propagation of stripe domain walls in staircaselike transitions of IrTe2

    NASA Astrophysics Data System (ADS)

    Mauerer, Tobias; Vogt, Matthias; Hsu, Pin-Jui; Pascut, Gheorghe Lucian; Haule, Kristjan; Kiryukhin, Valery; Yang, Junjie; Cheong, Sang-Wook; Wu, Weida; Bode, Matthias

    2016-07-01

    We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in IrTe2 that occur at TC≈275 K and TS≈180 K, respectively. Phase coexistence of the hexagonal (1 ×1 ) structure and the (5 ×1 ) stripe modulation is observed at TC, while various (p ×1 ) modulations (p =3 n +2 with 2 ≤n ∈N ) are observed below TS. Using STM atomic resolution, we observe anisotropic propagation of domain boundaries along different directions, indicating significantly different kinetic energy barriers. These results are consistently explained by a theoretical analysis of the energy barrier for domain wall propagation as obtained by density functional theory. Individual switching processes observed by STM indicate that the wide temperature range of the transition from the (5 ×1 ) stripes to the (6 ×1 ) -ordered ground state is probably caused by the numerically limited subset of switching processes that are allowed between a given initial and the final state. The observations on IrTe2 are discussed in terms of a "harmless staircase" with a finite number of first-order transitions between commensurate phases and within a "dynamical freezing" scenario.

  1. Using Item Response Theory (IRT) to Reduce Patient Burden When Assessing Desire for Hastened Death.

    PubMed

    Kolva, Elissa; Rosenfeld, Barry; Liu, Ying; Pessin, Hayley; Breitbart, William

    2016-06-09

    Desire for hastened death (DHD) represents a wish to die sooner than might occur by natural disease progression. Efficient and accurate assessment of DHD is vital for clinicians providing care to terminally ill patients. The Schedule of Attitudes Toward Hastened Death (SAHD) is a commonly used self-report measure of DHD. The goal of this study was to use methods grounded in item response theory (IRT) to analyze the psychometric properties of the SAHD and identify an abbreviated version of the scale. Data were drawn from 4 studies of psychological distress at the end of life. Participants were 1,076 patients diagnosed with either advanced cancer or AIDS. The sample was divided into 2 subsamples for scale analysis and development of the shortened form. IRT was used to estimate item parameters. A 6-item version of the SAHD (SAHD-A) was identified through examination of item parameter estimations. The SAHD-A demonstrated adequate convergent validity. Receiver operating characteristic analyses indicated comparable cut scores to identify patients with high levels of DHD. These analyses support the utility of the SAHD-A, which can be more easily integrated into research studies and clinical assessments of DHD. (PsycINFO Database Record

  2. The technique and preliminary results of LEU U-Mo full-size IRT type fuel testing in the MIR reactor

    SciTech Connect

    Izhutov, A.L.; Starkov, V.A.; Pimenov, V.V.; Fedoseev, V.Ye.; Dobrikova, I.V.; Vatulin, A.V.; Suprun, V.B.; Kartashov, Ye.F.; Lukichev, V.A.; Troyanov, V.M.; Enin, A.A.; Tkachev, A.A.

    2008-07-15

    In March 2007 in-pile testing of LEU U-Mo full-size IRT type fuel elements was started in the MIR reactor. Four prototype fuel elements for Uzbekistan WWR SM reactor are being tested simultaneously - two of tube type design and two of pin type design. The dismountable irradiation devices were constructed for intermediate reloading and inspection of fuel elements during reactor testing. The objective of the test is to obtain the experimental results for determination of more reliable design and licensing fuel elements for conversion of the WWR SM reactor. The heat power of fuel elements is measured on-line by thermal balance method. The distribution of fission density and burn-up of uranium in the volume of elements are calculated by using the MIR reactor MCU code (Monte-Carlo) model. In this paper the design of fuel elements, the technique, main parameters and preliminary results are described. (author)

  3. Investigating the Impact of Item Parameter Drift for Item Response Theory Models with Mixture Distributions

    PubMed Central

    Park, Yoon Soo; Lee, Young-Sun; Xing, Kuan

    2016-01-01

    This study investigates the impact of item parameter drift (IPD) on parameter and ability estimation when the underlying measurement model fits a mixture distribution, thereby violating the item invariance property of unidimensional item response theory (IRT) models. An empirical study was conducted to demonstrate the occurrence of both IPD and an underlying mixture distribution using real-world data. Twenty-one trended anchor items from the 1999, 2003, and 2007 administrations of Trends in International Mathematics and Science Study (TIMSS) were analyzed using unidimensional and mixture IRT models. TIMSS treats trended anchor items as invariant over testing administrations and uses pre-calibrated item parameters based on unidimensional IRT. However, empirical results showed evidence of two latent subgroups with IPD. Results also showed changes in the distribution of examinee ability between latent classes over the three administrations. A simulation study was conducted to examine the impact of IPD on the estimation of ability and item parameters, when data have underlying mixture distributions. Simulations used data generated from a mixture IRT model and estimated using unidimensional IRT. Results showed that data reflecting IPD using mixture IRT model led to IPD in the unidimensional IRT model. Changes in the distribution of examinee ability also affected item parameters. Moreover, drift with respect to item discrimination and distribution of examinee ability affected estimates of examinee ability. These findings demonstrate the need to caution and evaluate IPD using a mixture IRT framework to understand its effects on item parameters and examinee ability. PMID:26941699

  4. Effectiveness of Item Response Theory (IRT) Proficiency Estimation Methods under Adaptive Multistage Testing. Research Report. ETS RR-15-11

    ERIC Educational Resources Information Center

    Kim, Sooyeon; Moses, Tim; Yoo, Hanwook Henry

    2015-01-01

    The purpose of this inquiry was to investigate the effectiveness of item response theory (IRT) proficiency estimators in terms of estimation bias and error under multistage testing (MST). We chose a 2-stage MST design in which 1 adaptation to the examinees' ability levels takes place. It includes 4 modules (1 at Stage 1, 3 at Stage 2) and 3 paths…

  5. Fresh and Spent Nuclear Fuel Repatriation from the IRT-2000 Research Reactor Facility, Sofia, Bulgaria

    SciTech Connect

    K. J. Allen; T. G. Apostolov; I. S. Dimitrov

    2009-03-01

    The IRT 2000 research reactor, operated by the Bulgarian Institute for Nuclear Research and Nuclear Energy (INRNE), safely shipped all of their Russian-origin nuclear fuel from the Republic of Bulgaria to the Russian Federation beginning in 2003 and completing in 2008. These fresh and spent fuel shipments removed all highly enriched uranium (HEU) from Bulgaria. The fresh fuel was shipped by air in December 2003 using trucks and a commercial cargo aircraft. One combined spent fuel shipment of HEU and low enriched uranium (LEU) was completed in July 2008 using high capacity VPVR/M casks transported by truck, barge, and rail. The HEU shipments were assisted by the Russian Research Reactor Fuel Return Program (RRRFR) and the LEU spent fuel shipment was funded by Bulgaria. This report describes the work, approvals, organizations, equipment, and agreements required to complete these shipments and concludes with several major lessons learned.

  6. Far-Infrared [CII] Line Observation of the Galactic Plane by IRTS

    NASA Astrophysics Data System (ADS)

    Makiuti, Sin'itirou; Shibai, Hiroshi; Okuda, Haruyuki; Nakagawa, Takao; Matsuhara, Hideo; Hiromoto, Norihisa; Okumura, Ken'ichi

    1996-10-01

    A detailed map of the distribution of the [CII] 158 mu m line intensity from the galactic plane around l = 50(deg) was obtained by the Far-Infrared Line Mapper (FILM) on board the Infrared Telescope in Space (IRTS). The distribution of the [CII] emission is similar to that of the far-infrared continuum emission. There are a number of discrete sources, most of which correspond to known objects, such as compact HII regions and molecular clouds, near to the galactic plane. Moreover, an extended component concentrated in the galactic plane was found, and its distribution does not clearly depend on the galactic longitude in the observed area. This extended component decreases rapidly as the galactic latitude increases. The FWHM of this component is about 2.(deg) 6 in the galactic latitude. This is larger than that of the CO (J=1 -> 0) intensity, but is much smaller than that of the HI 21 cm intensity.

  7. 155 Micron Continuum Emission from the Galactic Plane near L = 50 Degrees Observed by IRTS

    NASA Astrophysics Data System (ADS)

    Okumura, Ken'ichi; Hiromoto, Norihisa; Okuda, Haruyuki; Shibai, Hiroshi; Nakagawa, Takao; Makiuti, Sin'itirou; Matsuhara, Hideo

    1996-12-01

    The 155 mu m continuum emission from the galactic plane around l = 50(deg) was observed with an 8'times13 ' beam by the Far-Infrared Line Mapper (FILM) aboard the Infrared Telescope in Space (IRTS). The observed map noticeably resembles the IRAS 100 mu m map. The dust temperature calculated from their flux ratio is almost constant (16--18 K) throughout the observed area, except for the HII regions. The dust temperatures in the HII regions are significantly higher than in the surrounding region; there is a clear boundary between the cold and hot regions. The observed uniformity of the dust temperature, except for in the HII regions, implies that the strength of the average interstellar radiation field (ISRF) along each line of sight is almost constant (i.e., varies by less than a factor of 2) in the observed region of the galactic plane.

  8. GPR and IRT tests in two historical buildings in Gravina in Puglia

    NASA Astrophysics Data System (ADS)

    Matera, Loredana; Persico, Raffaele; Geraldi, Edoardo; Sileo, Maria; Piro, Salvatore

    2016-11-01

    This paper describes a geophysical investigation conducted into two important churches, namely the Cathedral of Santa Maria Assunta and the Church of Santa Croce, both in Gravina in Puglia (close to Bari, southern Italy). The Church of Santa Croce, now deconsecrated, lies below the cathedral. Therefore, the two churches constitute a unique building body. Moreover, below the Church of Santa Croce there are several crypts, which are only partially known. The prospecting was performed both with a pulsed commercial ground penetrating radar (GPR) system and with a prototypal reconfigurable stepped frequency system. The aim was twofold, namely to gather information about the monument and to test the prototypal system. The GPR measurements have also been integrated with an infrared thermography (IRT) investigation performed on part of the vaulted ceiling in the Church of Santa Croce, in order to confirm or deny a possible interpretation of certain GPR results.

  9. A Far Infrared Photometer (FIRP) for the infrared telescope in space (IRTS)

    NASA Technical Reports Server (NTRS)

    Freund, M. M.; Hirao, T.; Matsumoto, T.; Sato, S.; Watabe, T.; Brubaker, G. K.; Duband, L.; Grossman, B.; Larkin, N.; Lumetta, S.

    1993-01-01

    We describe the design and calibration of the Far-Infrared Photometer (FIRP), one of four focal plane instruments on the Infrared Telescope in Space (IRTS). The FIRP will provide absolute photometry in four bands centered at 150, 250, 400, and 700 micrometers with spectral resolution lambda/(Delta lambda) approx. = 3 and spatial resolution Delta theta = 0.5 degrees. High sensitivity is achieved by using bolometric detectors operated at 300 mK in an AC bridge circuit. The closed-cycle He-3 refrigerator can be recycled in orbit. A 2 K shutter provides a zero reference for each field of view. More than 10% of the sky will be surveyed during the approximately 3 week mission lifetime with a sensitivity of less than 10(exp -13) W/((sq cm)(sr)) per 0.5 degree pixel.

  10. Measurement of gamma field parameters in core with LEU fuel IRT-4M using TL detectors

    SciTech Connect

    Bily, T.

    2008-07-15

    Thermoluminescent dosimeters represent very useful tool for gamma fields parameters measurements at nuclear research reactors, especially at zero power ones. {sup 7}LiF:Mg,Ti and {sup 7}LiF:Mg,Cu,P type TL dosimeters enable determination of only gamma component in mixed neutron - gamma field. At VR-1 reactor operated within the Faculty of Nuclear Sciences and Physical Engineering at the Czech Technical University in Prague the integral characteristics of gamma rays field were investigated, especially its spatial distribution and time behaviour, i.e. the non-saturated delayed gamma ray emission influence. Measured spatial distributions were compared with monte carlo code MCNP5 calculations. Although MCNP cannot generate delayed gamma rays from fission, the relative gamma dose rate distribution is within {+-} 15% with measured values. The experiments were carried out with core configuration C1 consisting of LEU fuel IRT-4M (19.7 %). (author)

  11. Fitting Item Response Models to the Maryland Functional Reading Test Results.

    ERIC Educational Resources Information Center

    Hambleton, Ronald K.; And Others

    The potential of item response theory (IRT) for solving a number of testing problems in the Maryland Functional Reading Program would appear to be substantial in view of the many other promising applications of the theory. But, it is well-known that the advantages derived from an IRT model cannot be achieved when the fit between an item response…

  12. Polarization of IRON-REGULATED TRANSPORTER 1 (IRT1) to the plant-soil interface plays crucial role in metal homeostasis.

    PubMed

    Barberon, Marie; Dubeaux, Guillaume; Kolb, Cornelia; Isono, Erika; Zelazny, Enric; Vert, Grégory

    2014-06-03

    In plants, the controlled absorption of soil nutrients by root epidermal cells is critical for growth and development. IRON-REGULATED TRANSPORTER 1 (IRT1) is the main root transporter taking up iron from the soil and is also the main entry route in plants for potentially toxic metals such as manganese, zinc, cobalt, and cadmium. Previous work demonstrated that the IRT1 protein localizes to early endosomes/trans-Golgi network (EE/TGN) and is constitutively endocytosed through a monoubiquitin- and clathrin-dependent mechanism. Here, we show that the availability of secondary non-iron metal substrates of IRT1 (Zn, Mn, and Co) controls the localization of IRT1 between the outer polar domain of the plasma membrane and EE/TGN in root epidermal cells. We also identify FYVE1, a phosphatidylinositol-3-phosphate-binding protein recruited to late endosomes, as an important regulator of IRT1-dependent metal transport and metal homeostasis in plants. FYVE1 controls IRT1 recycling to the plasma membrane and impacts the polar delivery of this transporter to the outer plasma membrane domain. This work establishes a functional link between the dynamics and the lateral polarity of IRT1 and the transport of its substrates, and identifies a molecular mechanism driving polar localization of a cell surface protein in plants.

  13. Polarization of IRON-REGULATED TRANSPORTER 1 (IRT1) to the plant-soil interface plays crucial role in metal homeostasis

    PubMed Central

    Barberon, Marie; Dubeaux, Guillaume; Kolb, Cornelia; Isono, Erika; Zelazny, Enric; Vert, Grégory

    2014-01-01

    In plants, the controlled absorption of soil nutrients by root epidermal cells is critical for growth and development. IRON-REGULATED TRANSPORTER 1 (IRT1) is the main root transporter taking up iron from the soil and is also the main entry route in plants for potentially toxic metals such as manganese, zinc, cobalt, and cadmium. Previous work demonstrated that the IRT1 protein localizes to early endosomes/trans-Golgi network (EE/TGN) and is constitutively endocytosed through a monoubiquitin- and clathrin-dependent mechanism. Here, we show that the availability of secondary non-iron metal substrates of IRT1 (Zn, Mn, and Co) controls the localization of IRT1 between the outer polar domain of the plasma membrane and EE/TGN in root epidermal cells. We also identify FYVE1, a phosphatidylinositol-3-phosphate-binding protein recruited to late endosomes, as an important regulator of IRT1-dependent metal transport and metal homeostasis in plants. FYVE1 controls IRT1 recycling to the plasma membrane and impacts the polar delivery of this transporter to the outer plasma membrane domain. This work establishes a functional link between the dynamics and the lateral polarity of IRT1 and the transport of its substrates, and identifies a molecular mechanism driving polar localization of a cell surface protein in plants. PMID:24843126

  14. Utility of a very high IRT/No mutation referral category in cystic fibrosis newborn screening.

    PubMed

    Kay, Denise M; Langfelder-Schwind, Elinor; DeCelie-Germana, Joan; Sharp, Jack K; Maloney, Breanne; Tavakoli, Norma P; Saavedra-Matiz, Carlos A; Krein, Lea M; Caggana, Michele; Kier, Catherine

    2015-08-01

    Newborn screening for Cystic Fibrosis (CF) began in New York in October, 2002 using immunoreactive trypsinogen (IRT)/DNA methodology. Infants with at least one CFTR mutation or very high IRT and no mutations (VHIRT) are referred for sweat testing. In a preliminary analysis, we noted a very low positive predictive value (PPV) and preponderance of Hispanic infants in the group of infants with CF referred for VHIRT, which led to a decision to revise, but not eliminate, the VHIRT category. Automatic referral for specimens with VHIRT collected on the day of birth was eliminated, and the VHIRT threshold was raised from 0.2% to 0.1%. In this report, we describe outcomes from VHIRT referrals among 2.4 million infants screened between March 2003 and February 2013. Following the algorithm change, referrals decreased by 37.8% overall (annual mean 1,485 vs. 923), and the VHIRT PPV improved (0.6-1.0%). The number of infants diagnosed has remained consistent at 1 in 4,400 births. The proportion of Black/Hispanic/Asian/Other infants with confirmed CF, CFTR-related metabolic syndrome (CRMS), or possible CF/CRMS was 21.3% in infants with 1-2 mutations, but 75.8% in the VHIRT group. In conclusion, although the PPV among VHIRT referrals remains low, had this category never been implemented, 24 infants with confirmed CF, and 9 infants with CRMS or possible CF/CRMS, most of whom were Hispanic, would have been missed over the 10 years. Information from this study may be helpful in assessing the need for the VHIRT category and algorithm changes in other screening programs.

  15. Exogenous abscisic acid application decreases cadmium accumulation in Arabidopsis plants, which is associated with the inhibition of IRT1-mediated cadmium uptake.

    PubMed

    Fan, Shi Kai; Fang, Xian Zhi; Guan, Mei Yan; Ye, Yi Quan; Lin, Xian Yong; Du, Shao Ting; Jin, Chong Wei

    2014-01-01

    Cadmium (Cd) contamination of agricultural soils is an increasingly serious problem. Measures need to be developed to minimize Cd entering the human food chain from contaminated soils. We report here that, under Cd exposure condition, application with low doses of (0.1-0.5 μM) abscisic acid (ABA) clearly inhibited Cd uptake by roots and decreased Cd level in Arabidopsis wild-type plants (Col-0). Expression of IRT1 in roots was also strongly inhibited by ABA treatment. Decrease in Cd uptake and the inhibition of IRT1 expression were clearly lesser pronounced in an ABA-insensitive double mutant snrk2.2/2.3 than in the Col-0 in response to ABA application. The ABA-decreased Cd uptake was found to correlate with the ABA-inhibited IRT1 expression in the roots of Col-0 plants fed two different levels of iron. Furthermore, the Cd uptake of irt1 mutants was barely affected by ABA application. These results indicated that inhibition of IRT1 expression is involved in the decrease of Cd uptake in response to exogenous ABA application. Interestingly, ABA application increased the iron level in both Col-0 plants and irt1 mutants, suggesting that ABA-increased Fe acquisition does not depend on the IRT1 function, but on the contrary, the ABA-mediated inhibition of IRT1 expression may be due to the elevation of iron level in plants. From our results, we concluded that ABA application might increase iron acquisition, followed by the decrease in Cd uptake by inhibition of IRT1 activity. Thus, for crop production in Cd contaminated soils, developing techniques based on ABA application potentially is a promising approach for reducing Cd accumulation in edible organs in plants.

  16. A quantitative analysis of IRT data for the evaluation of plaster degradation at the Dome of Magdeburg (Germany)

    NASA Astrophysics Data System (ADS)

    Di Maio, Rosa; Maierhofer, Christiane; Mancini, Cecilia; Piegari, Ester

    2013-04-01

    Infrared Thermography (IRT) is a helpful method for the nondestructive evaluation of artworks and buildings of historical interest since it is able to provide indications about most of degradation sources, such as alteration of material consistency, formation of microcracks, debondings, etc. The most used procedures for physical and geometrical characterization of the thermal anomaly sources are based on numerical models that solve the forward thermal problem, i.e. they find the solution of the Fourier differential equation, which describes the heat transfer in a medium. In this framework, we present a Finite Difference method to evaluate the conservation state of the Dome of Magdeburg (Germany). In particular, the study is focused on the analysis of the thermal images acquired on the east wing of the cloister from the 13th century, and is aimed to characterize its plaster score. The structure was heated with an infrared radiator and thermal images were acquired on both heating and cooling phase for fifteen minutes. The proposed conservative FD method allows taking into account for varying thermal conductivity, density and specific heat of defects and disrupted materials. The heat transfer problem is formulated in one and two dimensions and, therefore, it is able to characterize multi-layered structures. The investigated structure is made of three plaster layers (one lime wash layer that overlaps two lime mortar layers) and a sandstone background. Numerical simulations have shown a very good match between the experimental and theoretical curves for all the considered anomalous areas, for both 1D and 2D formulations, providing an average percentage error of the order of 10-1%. In particular, the study allowed to define thickness, depth and nature (density, thermal conductivity and specific heat) of the thermal anomaly sources, attributable to the degradation of the lime mortar layer at different depths. The application of the codes provided helpful indications for

  17. Alternative Measurement Paradigms for Measuring Executive Functions: SEM (Formative and Reflective Models) and IRT (Rasch Models)

    ERIC Educational Resources Information Center

    Engelhard, George, Jr.; Wang, Jue

    2014-01-01

    The authors of the Focus article pose important questions regarding whether or not performance-based tasks related to executive functioning are best viewed as reflective or formative indicators. Miyake and Friedman (2012) define executive functioning (EF) as "a set of general-purpose control mechanisms, often linked to the prefrontal cortex…

  18. Using item response theory to investigate the structure of anticipated affect: do self-reports about future affective reactions conform to typical or maximal models?

    PubMed Central

    Zampetakis, Leonidas A.; Lerakis, Manolis; Kafetsios, Konstantinos; Moustakis, Vassilis

    2015-01-01

    In the present research, we used item response theory (IRT) to examine whether effective predictions (anticipated affect) conforms to a typical (i.e., what people usually do) or a maximal behavior process (i.e., what people can do). The former, correspond to non-monotonic ideal point IRT models, whereas the latter correspond to monotonic dominance IRT models. A convenience, cross-sectional student sample (N = 1624) was used. Participants were asked to report on anticipated positive and negative affect around a hypothetical event (emotions surrounding the start of a new business). We carried out analysis comparing graded response model (GRM), a dominance IRT model, against generalized graded unfolding model, an unfolding IRT model. We found that the GRM provided a better fit to the data. Findings suggest that the self-report responses to anticipated affect conform to dominance response process (i.e., maximal behavior). The paper also discusses implications for a growing literature on anticipated affect. PMID:26441806

  19. Linking Parameters Estimated with the Generalized Graded Unfolding Model: A Comparison of the Accuracy of Characteristic Curve Methods

    ERIC Educational Resources Information Center

    Anderson Koenig, Judith; Roberts, James S.

    2007-01-01

    Methods for linking item response theory (IRT) parameters are developed for attitude questionnaire responses calibrated with the generalized graded unfolding model (GGUM). One class of IRT linking methods derives the linking coefficients by comparing characteristic curves, and three of these methods---test characteristic curve (TCC), item…

  20. Estimation of a Ramsay-Curve Item Response Theory Model by the Metropolis-Hastings Robbins-Monro Algorithm

    ERIC Educational Resources Information Center

    Monroe, Scott; Cai, Li

    2014-01-01

    In Ramsay curve item response theory (RC-IRT) modeling, the shape of the latent trait distribution is estimated simultaneously with the item parameters. In its original implementation, RC-IRT is estimated via Bock and Aitkin's EM algorithm, which yields maximum marginal likelihood estimates. This method, however, does not produce the…

  1. Rasch Model Parameter Estimation in the Presence of a Nonnormal Latent Trait Using a Nonparametric Bayesian Approach

    ERIC Educational Resources Information Center

    Finch, Holmes; Edwards, Julianne M.

    2016-01-01

    Standard approaches for estimating item response theory (IRT) model parameters generally work under the assumption that the latent trait being measured by a set of items follows the normal distribution. Estimation of IRT parameters in the presence of nonnormal latent traits has been shown to generate biased person and item parameter estimates. A…

  2. Salient Features of the Harnischfeger-Wiley Model

    ERIC Educational Resources Information Center

    Hallinan, Maureen T.

    1976-01-01

    Explicates the Harnischfeger-Wiley model and points out its properties, underlying assumptions, and location in the literature on achievement. It also describes and critiques an empirical test by Harnischfeger and Wiley of their model. (Author/IRT)

  3. A Review of the Effects on IRT Item Parameter Estimates with a Focus on Misbehaving Common Items in Test Equating

    PubMed Central

    Michaelides, Michalis P.

    2010-01-01

    Many studies have investigated the topic of change or drift in item parameter estimates in the context of item response theory (IRT). Content effects, such as instructional variation and curricular emphasis, as well as context effects, such as the wording, position, or exposure of an item have been found to impact item parameter estimates. The issue becomes more critical when items with estimates exhibiting differential behavior across test administrations are used as common for deriving equating transformations. This paper reviews the types of effects on IRT item parameter estimates and focuses on the impact of misbehaving or aberrant common items on equating transformations. Implications relating to test validity and the judgmental nature of the decision to keep or discard aberrant common items are discussed, with recommendations for future research into more informed and formal ways of dealing with misbehaving common items. PMID:21833230

  4. Energetic electrons, hard x-ray emission and MHD activity studies in the IR-T1 tokamak.

    PubMed

    Agah, K Mikaili; Ghoranneviss, M; Elahi, A Salar

    2015-01-01

    Determinations of plasma parameters as well as the Magnetohydrodynamics (MHD) activity, energetic electrons energy and energy confinement time are essential for future fusion reactors experiments and optimized operation. Also some of the plasma information can be deduced from these parameters, such as plasma equilibrium, stability, and MHD instabilities. In this contribution we investigated the relation between energetic electrons, hard x-ray emission and MHD activity in the IR-T1 Tokamak. For this purpose we used the magnetic diagnostics and a hard x-ray spectroscopy in IR-T1 tokamak. A hard x-ray emission is produced by collision of the runaway electrons with the plasma particles or limiters. The mean energy was calculated from the slope of the energy spectrum of hard x-ray photons.

  5. Analysis Test of Understanding of Vectors with the Three-Parameter Logistic Model of Item Response Theory and Item Response Curves Technique

    ERIC Educational Resources Information Center

    Rakkapao, Suttida; Prasitpong, Singha; Arayathanitkul, Kwan

    2016-01-01

    This study investigated the multiple-choice test of understanding of vectors (TUV), by applying item response theory (IRT). The difficulty, discriminatory, and guessing parameters of the TUV items were fit with the three-parameter logistic model of IRT, using the parscale program. The TUV ability is an ability parameter, here estimated assuming…

  6. Estimation of a Ramsay-Curve Item Response Theory Model by the Metropolis-Hastings Robbins-Monro Algorithm. CRESST Report 834

    ERIC Educational Resources Information Center

    Monroe, Scott; Cai, Li

    2013-01-01

    In Ramsay curve item response theory (RC-IRT, Woods & Thissen, 2006) modeling, the shape of the latent trait distribution is estimated simultaneously with the item parameters. In its original implementation, RC-IRT is estimated via Bock and Aitkin's (1981) EM algorithm, which yields maximum marginal likelihood estimates. This method, however,…

  7. Immunolocalization of H(+)-ATPase and IRT1 enzymes in N(2)-fixing common bean nodules subjected to iron deficiency.

    PubMed

    Slatni, Tarek; Dell'Orto, Marta; Ben Salah, Imen; Vigani, Gianpiero; Smaoui, Abderrazak; Gouia, Houda; Zocchi, Graziano; Abdelly, Chedly

    2012-02-15

    The demand for iron in leguminous plants increases during symbiosis, as the metal is utilised for the synthesis of various Fe-containing proteins in both plant and bacteroids. However, the acquisition of this micronutrient is problematic due to its low bioavailability at physiological pH under aerobic conditions. Induction of root Fe(III)-reductase activity is necessary for Fe uptake and can be coupled to the rhizosphere acidification capacity linked to the H(+)-ATPase activity. Fe uptake is related to the expression of a Fe(2+) transporter (IRT1). In order to verify the possible role of nodules in the acquisition of Fe directly from the soil solution, the localization of H(+)-ATPase and IRT1 was carried out in common bean nodules by immuno-histochemical analysis. The results showed that these proteins were particularly abundant in the central nitrogen-fixing zone of nodules, around the periphery of infected and uninfected cells as well as in the vascular bundle of control nodules. Under Fe deficiency an over-accumulation of H(+)-ATPase and IRT1 proteins was observed especially around the cortex cells of nodules. The results obtained in this study suggest that the increase in these proteins is differentially localized in nodules of Fe-deficient plants when compared to the Fe-sufficient condition and cast new light on the possible involvement of nodules in the direct acquisition of Fe from the nutrient solution.

  8. A Study of Large Droplet Ice Accretions in the NASA-Lewis IRT at Near-Freezing Conditions

    NASA Technical Reports Server (NTRS)

    Miller, Dean R.; Addy, Harold E. , Jr.; Ide, Robert F.

    1996-01-01

    This report documents the results of an experimental study on large droplet ice accretions which was conducted in the NASA-Lewis Icing Research Tunnel (IRT) with a full-scale 77.25 inch chord Twin-Otter wing section. This study was intended to: (1) document the existing capability of the IRT to produce a large droplet icing cloud, and (2) study the effect of various parameters on large droplet ice accretions. Results are presented from a study of the IRT's capability to produce large droplets with MVD of 99 and 160 microns. The effect of the initial water droplet temperature on the resultant ice accretion was studied for different initial spray bar air and water temperatures. The initial spray bar water temperature was found to have no discernible effect upon the large droplet ice accretions. Also, analytical and experimental results suggest that the water droplet temperature is very nearly the same as the tunnel ambient temperature, thus providing a realistic simulation of the large droplet natural icing condition. The effect of temperature, droplet size, airspeed, angle-of attack, flap setting and de-icer boot cycling time on ice accretion was studied, and will be discussed in this report. It was found that, in almost all of the cases studied, an ice ridge formed immediately aft of the active portion of the de-icer boot. This ridge was irregular in shape, varied in location, and was in some cases discontinuous due to aerodynamic shedding.

  9. Investigation on the effect of pressure on turbulent transports of the IR-T1 Tokamak plasma

    NASA Astrophysics Data System (ADS)

    Alipour, Ramin; Meshkani, Sakineh; Elahi, Ahmad Salar; Ghoranneviss, Mahmood

    2017-03-01

    Investigation on the effects of limiter biasing and applying external electric fields (positive and negative voltage of 200 V) under various pressures of 1.9, 2.3 and 2.7 Torr on the IR-T1 Tokamak plasma parameters such as plasma current, loop voltage, radial electric field, poloidal electric field and Reynolds stress and turbulent transports, was done in this work. The results show that the ramp time of the plasma current decreased and the change rate of loop voltage raised by increasing plasma pressure. The power of radial electric field is more than the power of poloidal electric field. According to the applied positive voltage to the plasma, it is observed that the Reynolds stress of IR-T1 Tokamak plasma has experienced a more significant reduction at the pressure of 2.3 Torr than other pressures. The results Also show that the applying positive voltage of 200 V to the IR-T1 Tokamak plasma at the pressure of 2.3 Torr (compared to other pressures) has more effect on increases and decreases the poloidal and radial turbulent transport, respectively.

  10. The first critical experiment with a LEU Russian fuel IRT-4M at the training reactor VR-1

    SciTech Connect

    Frybort, Jan

    2008-07-15

    A critical experiment is a standard part of training of students at the Training Reactor VR-1 operated within the Faculty of Nuclear Sciences and Physical Engineering at the Czech Technical University in Prague. In autumn 2005 the HEU fuel IRT-3M with enrichment 36 % {sup 235}U was replaced by the LEU fuel IRT-4M with enrichment 19.7 % {sup 235}U. The fuel replacement at the VR-1 Reactor is a part of an international program RERTR. This Paper presents basic information about preparation for the fuel replacement and approaching of the first critical state with the new zone configuration C1 which replaced B1 core with the old IRT-3M fuel. The whole process was carried out according to the Czech law and the relevant international recommendations. The experience with the VR-1 operation confirms the assumption that the C1 core configuration will be suitable from the point of view of the reactivity balance for the long term safe operation of the Training Reactor VR-1. (author)

  11. Determination of the heat transfer coefficient from IRT measurement data using the Trefftz method

    NASA Astrophysics Data System (ADS)

    Maciejewska, Beata; Strąk, Kinga; Piasecka, Magdalena

    2016-03-01

    The paper presents the method of heat transfer coefficient determination for boiling research during FC-72 flow in the minichannels, each 1.7 mm deep, 24 mm wide and 360 mm long. The heating element was the thin foil, enhanced on the side which comes into contact with fluid in the minichannels. Local values of the heat transfer coefficient were calculated from the Robin boundary condition. The foil temperature distribution and the derivative of the foil temperature were obtained by solving the two-dimensional inverse heat conduction problem, due to measurements obtained by IRT. Calculations was carried out by the method based on the approximation of the solution of the problem using a linear combination of Trefftz functions. The basic property of this functions is they satisfy the governing equation. Unknown coefficients of linear combination of Trefftz functions are calculated from the minimization of the functional that expresses the mean square error of the approximate solution on the boundary. The results presented as IR thermographs, two-phase flow structure images and the heat transfer coefficient as a function of the distance from the channel inlet, were analyzed.

  12. Selective electrodiffusion of zinc ions in a Zrt-, Irt-like protein, ZIPB

    SciTech Connect

    Lin, W.; Fu, D.; Chai, J.; Love, J.

    2010-12-10

    All living cells need zinc ions to support cell growth. Zrt-, Irt-like proteins (ZIPs) represent a major route for entry of zinc ions into cells, but how ZIPs promote zinc uptake has been unclear. Here we report the molecular characterization of ZIPB from Bordetella bronchiseptica, the first ZIP homolog to be purified and functionally reconstituted into proteoliposomes. Zinc flux through ZIPB was found to be nonsaturable and electrogenic, yielding membrane potentials as predicted by the Nernst equation. Conversely, membrane potentials drove zinc fluxes with a linear voltage-flux relationship. Direct measurements of metal uptake by inductively coupled plasma mass spectroscopy demonstrated that ZIPB is selective for two group 12 transition metal ions, Zn{sup 2+} and Cd{sup 2+}, whereas rejecting transition metal ions in groups 7 through 11. Our results provide the molecular basis for cellular zinc acquisition by a zinc-selective channel that exploits in vivo zinc concentration gradients to move zinc ions into the cytoplasm.

  13. Synthesis of monoclinic IrTe2 under high pressure and its physical properties

    DOE PAGES

    Li, X.; Yan, J. -Q.; Singh, D. J.; ...

    2015-10-12

    In a pressure-temperature (P-T) diagram for synthesizing IrTe2 compounds, the well-studied trigonal (H) phase with the CdI2-type structure is stable at low pressures. The superconducting cubic (C) phase can be synthesized under higher temperatures and pressures. A rhombohedral phase with the crystal structure similar to the C phase can be made at ambient pressure; but the phase contains a high concentration of Ir deficiency. Here, we report that a rarely studied monoclinic (M) phase can be stabilized in narrow ranges of pressure and temperature in this P-T diagram. Moreover, the peculiar crystal structure of the M-IrTe2 eliminates the tendency tomore » form Ir-Ir dimers found in the H phase. The M phase has been fully characterized by structural determination and measurements of electrical resistivity, thermoelectric power, DC magnetization, and specific heat. These physical properties have been compared with those in the H and C phases of Ir1-xTe2. Finally, we present magnetic and transport properties and specific heat of the M-IrTe2 can be fully justified by calculations with the density-functional theory.« less

  14. NOD promoter-controlled AtIRT1 expression functions synergistically with NAS and FERRITIN genes to increase iron in rice grains.

    PubMed

    Boonyaves, Kulaporn; Gruissem, Wilhelm; Bhullar, Navreet K

    2016-02-01

    Rice is a staple food for over half of the world's population, but it contains only low amounts of bioavailable micronutrients for human nutrition. Consequently, micronutrient deficiency is a widespread health problem among people who depend primarily on rice as their staple food. Iron deficiency anemia is one of the most serious forms of malnutrition. Biofortification of rice grains for increased iron content is an effective strategy to reduce iron deficiency. Unlike other grass species, rice takes up iron as Fe(II) via the IRON REGULATED TRANSPORTER (IRT) in addition to Fe(III)-phytosiderophore chelates. We expressed Arabidopsis IRT1 (AtIRT1) under control of the Medicago sativa EARLY NODULIN 12B promoter in our previously developed high-iron NFP rice lines expressing NICOTIANAMINE SYNTHASE (AtNAS1) and FERRITIN. Transgenic rice lines expressing AtIRT1 alone had significant increases in iron and combined with NAS and FERRITIN increased iron to 9.6 µg/g DW in the polished grains that is 2.2-fold higher as compared to NFP lines. The grains of AtIRT1 lines also accumulated more copper and zinc but not manganese. Our results demonstrate that the concerted expression of AtIRT1, AtNAS1 and PvFERRITIN synergistically increases iron in both polished and unpolished rice grains. AtIRT1 is therefore a valuable transporter for iron biofortification programs when used in combination with other genes encoding iron transporters and/or storage proteins.

  15. Galactic mass-losing AGB stars probed with the IRTS. II.

    NASA Astrophysics Data System (ADS)

    Le Bertre, T.; Tanaka, M.; Yamamura, I.; Murakami, H.

    2003-06-01

    We are using the 2002 data-release from the Japanese space experiment IRTS to investigate the spatial distribution of galactic mass-losing (>2x 10-8 Msund) AGB stars and the relative contribution of C-rich and O-rich ones to the replenishment of the ISM. Our sample contains 126 C-rich and 563 O-rich sources which are sorted on the basis of the molecular bands observed in the range 1.4-4.0 mu m, and for which we estimate distances and mass loss rates from near-infrared photometry (K and L'). There is a clear dependence on galactocentric distance, with O-rich sources outnumbering C-rich ones for rGC< 8 kpc, and the reverse for rGC> 10 kpc. The contribution to the replenishment of the ISM by O-rich AGB stars relative to C-rich ones follows the same trend. Although they are rare ( ~ 10% in our sample), sources with 10-6 Msund < dot {M} < 10-5 Msund dominate the replenishment of the ISM by contributing to ~ 50% of the total of the complete sample. We find 2 carbon stars at more than 1 kpc from the Galactic Plane, that probably belong to the halo of our Galaxy. The complete Tables \\ref{tab_C-rich} and \\ref{tab_O-rich} are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/943}

  16. Using a Mixture IRT Model to Improve Parameter Estimates when Some Examinees Are Amotivated

    ERIC Educational Resources Information Center

    Lau, Abigail

    2009-01-01

    Test-takers can be required to complete a test form, but cannot be forced to demonstrate their knowledge. Even if an authority mandates completion of a test, examinees can still opt to enter responses randomly. When a test has important consequences for individuals, examinees are unlikely to behave this way. However, random responding becomes more…

  17. Between-Person and Within-Person Subscore Reliability: Comparison of Unidimensional and Multidimensional IRT Models

    ERIC Educational Resources Information Center

    Bulut, Okan

    2013-01-01

    The importance of subscores in educational and psychological assessments is undeniable. Subscores yield diagnostic information that can be used for determining how each examinee's abilities/skills vary over different content domains. One of the most common criticisms about reporting and using subscores is insufficient reliability of subscores.…

  18. Parameter Estimation with Small Sample Size: A Higher-Order IRT Model Approach

    ERIC Educational Resources Information Center

    de la Torre, Jimmy; Hong, Yuan

    2010-01-01

    Sample size ranks as one of the most important factors that affect the item calibration task. However, due to practical concerns (e.g., item exposure) items are typically calibrated with much smaller samples than what is desired. To address the need for a more flexible framework that can be used in small sample item calibration, this article…

  19. Taylor Approximations to Logistic IRT Models and Their Use in Adaptive Testing.

    ERIC Educational Resources Information Center

    Veerkamp, Wim J. J.

    2000-01-01

    Showed how Taylor approximation can be used to generate a linear approximation to a logistic item characteristic curve and a linear ability estimator. Demonstrated how, for a specific simulation, this could result in the special case of a Robbins-Monro item selection procedure for adaptive testing. (SLD)

  20. Simultaneous Estimation of Overall and Domain Abilities: A Higher-Order IRT Model Approach

    ERIC Educational Resources Information Center

    de la Torre, Jimmy; Song, Hao

    2009-01-01

    Assessments consisting of different domains (e.g., content areas, objectives) are typically multidimensional in nature but are commonly assumed to be unidimensional for estimation purposes. The different domains of these assessments are further treated as multi-unidimensional tests for the purpose of obtaining diagnostic information. However, when…

  1. A Comparative Study of Test Data Dimensionality Assessment Procedures Under Nonparametric IRT Models

    ERIC Educational Resources Information Center

    van Abswoude, Alexandra A. H.; van der Ark, L. Andries; Sijtsma, Klaas

    2004-01-01

    In this article, an overview of nonparametric item response theory methods for determining the dimensionality of item response data is provided. Four methods were considered: MSP, DETECT, HCA/CCPROX, and DIMTEST. First, the methods were compared theoretically. Second, a simulation study was done to compare the effectiveness of MSP, DETECT, and…

  2. Evaluating College Services Using Student Ratings with Incomplete Data: An IRT Rating Scale Model Approach.

    ERIC Educational Resources Information Center

    Sun, Anji; Schulz, E. Matthew

    Missing data create problems for the interpretations and inferences of survey results, especially if the amount of missing data is substantial. This study considers issues of missing data when comparisons are made across survey items. It is suggested that if the groups responding to different items differ in their tendency to use one end of the…

  3. Dimensionality of the Latent Structure and Item Selection via Latent Class Multidimensional IRT Models

    ERIC Educational Resources Information Center

    Bartolucci, F.; Montanari, G. E.; Pandolfi, S.

    2012-01-01

    With reference to a questionnaire aimed at assessing the performance of Italian nursing homes on the basis of the health conditions of their patients, we investigate two relevant issues: dimensionality of the latent structure and discriminating power of the items composing the questionnaire. The approach is based on a multidimensional item…

  4. Modeling Nonignorable Missing Data with Item Response Theory (IRT). Research Report. ETS RR-10-11

    ERIC Educational Resources Information Center

    Rose, Norman; von Davier, Matthias; Xu, Xueli

    2010-01-01

    Large-scale educational surveys are low-stakes assessments of educational outcomes conducted using nationally representative samples. In these surveys, students do not receive individual scores, and the outcome of the assessment is inconsequential for respondents. The low-stakes nature of these surveys, as well as variations in average performance…

  5. Validation of deterministic and Monte Carlo codes for neutronics calculation of the IRT-type research reactor

    NASA Astrophysics Data System (ADS)

    Shchurovskaya, M. V.; Alferov, V. P.; Geraskin, N. I.; Radaev, A. I.

    2017-01-01

    The results of the validation of a research reactor calculation using Monte Carlo and deterministic codes against experimental data and based on code-to-code comparison are presented. The continuous energy Monte Carlo code MCU-PTR and the nodal diffusion-based deterministic code TIGRIS were used for full 3-D calculation of the IRT MEPhI research reactor. The validation included the investigations for the reactor with existing high enriched uranium (HEU, 90 w/o) fuel and low enriched uranium (LEU, 19.7 w/o, U-9%Mo) fuel.

  6. A quantitative comparison of noise reduction across five commercial (hybrid and model-based) iterative reconstruction techniques: an anthropomorphic phantom study.

    PubMed

    Patino, Manuel; Fuentes, Jorge M; Hayano, Koichi; Kambadakone, Avinash R; Uyeda, Jennifer W; Sahani, Dushyant V

    2015-02-01

    OBJECTIVE. The objective of our study was to compare the performance of three hybrid iterative reconstruction techniques (IRTs) (ASiR, iDose4, SAFIRE) and their respective strengths for image noise reduction on low-dose CT examinations using filtered back projection (FBP) as the standard reference. Also, we compared the performance of these three hybrid IRTs with two model-based IRTs (Veo and IMR) for image noise reduction on low-dose examinations. MATERIALS AND METHODS. An anthropomorphic abdomen phantom was scanned at 100 and 120 kVp and different tube current-exposure time products (25-100 mAs) on three CT systems (for ASiR and Veo, Discovery CT750 HD; for iDose4 and IMR, Brilliance iCT; and for SAFIRE, Somatom Definition Flash). Images were reconstructed using FBP and using IRTs at various strengths. Nine noise measurements (mean ROI size, 423 mm(2)) on extracolonic fat for the different strengths of IRTs were recorded and compared with FBP using ANOVA. Radiation dose, which was measured as the volume CT dose index and dose-length product, was also compared. RESULTS. There were no significant differences in radiation dose and image noise among the scanners when FBP was used (p > 0.05). Gradual image noise reduction was observed with each increasing increment of hybrid IRT strength, with a maximum noise suppression of approximately 50% (48.2-53.9%). Similar noise reduction was achieved on the scanners by applying specific hybrid IRT strengths. Maximum noise reduction was higher on model-based IRTs (68.3-81.1%) than hybrid IRTs (48.2-53.9%) (p < 0.05). CONCLUSION. When constant scanning parameters are used, radiation dose and image noise on FBP are similar for CT scanners made by different manufacturers. Significant image noise reduction is achieved on low-dose CT examinations rendered with IRTs. The image noise on various scanners can be matched by applying specific hybrid IRT strengths. Model-based IRTs attain substantially higher noise reduction than hybrid

  7. The high-affinity metal Transporters NRAMP1 and IRT1 Team up to Take up Iron under Sufficient Metal Provision

    PubMed Central

    Castaings, Loren; Caquot, Antoine; Loubet, Stéphanie; Curie, Catherine

    2016-01-01

    Iron (Fe) and manganese (Mn) are essential metals which, when scarce in the growth medium, are respectively taken up by the root high affinity transporters IRT1 and NRAMP1 in Arabidopsis thaliana. The molecular bases for low affinity transport however remained unknown. Since IRT1 and NRAMP1 have a broad range of substrates among metals, we tested the hypothesis that they might be functionally redundant by generating nramp1 irt1 double mutants. These plants showed extreme Fe-deficiency symptoms despite optimal provision of the metal. Their phenotype, which includes low Fe and Mn contents and a defect of Fe entry into root cells as revealed by Fe staining, is rescued by high Fe supply. Using a promoter swap-based strategy, we showed that root endodermis retains the ability to carry out high affinity Fe transport and furthermore might be important to high-affinity Mn uptake. We concluded that NRAMP1 plays a pivotal role in Fe transport by cooperating with IRT1 to take up Fe in roots under replete conditions, thus providing the first evidence for a low affinity Fe uptake system in plants. PMID:27849020

  8. A Comparison between Linear IRT Observed-Score Equating and Levine Observed-Score Equating under the Generalized Kernel Equating Framework

    ERIC Educational Resources Information Center

    Chen, Haiwen

    2012-01-01

    In this article, linear item response theory (IRT) observed-score equating is compared under a generalized kernel equating framework with Levine observed-score equating for nonequivalent groups with anchor test design. Interestingly, these two equating methods are closely related despite being based on different methodologies. Specifically, when…

  9. High-precision iRT prediction in the targeted analysis of data-independent acquisition and its impact on identification and quantitation.

    PubMed

    Bruderer, Roland; Bernhardt, Oliver M; Gandhi, Tejas; Reiter, Lukas

    2016-08-01

    Targeted analysis of data-independent acquisition (DIA) data is a powerful mass spectrometric approach for comprehensive, reproducible and precise proteome quantitation. It requires a spectral library, which contains for all considered peptide precursor ions empirically determined fragment ion intensities and their predicted retention time (RT). RTs, however, are not comparable on an absolute scale, especially if heterogeneous measurements are combined. Here, we present a method for high-precision prediction of RT, which significantly improves the quality of targeted DIA analysis compared to in silico RT prediction and the state of the art indexed retention time (iRT) normalization approach. We describe a high-precision normalized RT algorithm, which is implemented in the Spectronaut software. We, furthermore, investigate the influence of nine different experimental factors, such as chromatographic mobile and stationary phase, on iRT precision. In summary, we show that using targeted analysis of DIA data with high-precision iRT significantly increases sensitivity and data quality. The iRT values are generally transferable across a wide range of experimental conditions. Best results, however, are achieved if library generation and analytical measurements are performed on the same system.

  10. The Construction of Parallel Tests from IRT-Based Item Banks. Project Psychometric Aspects of Item Banking No. 43. Research Report 89-2.

    ERIC Educational Resources Information Center

    Boekkooi-Timminga, Ellen

    The construction of parallel tests from item response theory (IRT) based item banks is discussed. Tests are considered parallel whenever their information functions are identical. After the methods for constructing parallel tests are considered, the computational complexity of 0-1 linear programming and the heuristic procedure applied are…

  11. The high-affinity metal Transporters NRAMP1 and IRT1 Team up to Take up Iron under Sufficient Metal Provision.

    PubMed

    Castaings, Loren; Caquot, Antoine; Loubet, Stéphanie; Curie, Catherine

    2016-11-16

    Iron (Fe) and manganese (Mn) are essential metals which, when scarce in the growth medium, are respectively taken up by the root high affinity transporters IRT1 and NRAMP1 in Arabidopsis thaliana. The molecular bases for low affinity transport however remained unknown. Since IRT1 and NRAMP1 have a broad range of substrates among metals, we tested the hypothesis that they might be functionally redundant by generating nramp1 irt1 double mutants. These plants showed extreme Fe-deficiency symptoms despite optimal provision of the metal. Their phenotype, which includes low Fe and Mn contents and a defect of Fe entry into root cells as revealed by Fe staining, is rescued by high Fe supply. Using a promoter swap-based strategy, we showed that root endodermis retains the ability to carry out high affinity Fe transport and furthermore might be important to high-affinity Mn uptake. We concluded that NRAMP1 plays a pivotal role in Fe transport by cooperating with IRT1 to take up Fe in roots under replete conditions, thus providing the first evidence for a low affinity Fe uptake system in plants.

  12. High‐precision iRT prediction in the targeted analysis of data‐independent acquisition and its impact on identification and quantitation

    PubMed Central

    Bruderer, Roland; Bernhardt, Oliver M.; Gandhi, Tejas

    2016-01-01

    Targeted analysis of data‐independent acquisition (DIA) data is a powerful mass spectrometric approach for comprehensive, reproducible and precise proteome quantitation. It requires a spectral library, which contains for all considered peptide precursor ions empirically determined fragment ion intensities and their predicted retention time (RT). RTs, however, are not comparable on an absolute scale, especially if heterogeneous measurements are combined. Here, we present a method for high‐precision prediction of RT, which significantly improves the quality of targeted DIA analysis compared to in silico RT prediction and the state of the art indexed retention time (iRT) normalization approach. We describe a high‐precision normalized RT algorithm, which is implemented in the Spectronaut software. We, furthermore, investigate the influence of nine different experimental factors, such as chromatographic mobile and stationary phase, on iRT precision. In summary, we show that using targeted analysis of DIA data with high‐precision iRT significantly increases sensitivity and data quality. The iRT values are generally transferable across a wide range of experimental conditions. Best results, however, are achieved if library generation and analytical measurements are performed on the same system. PMID:27213465

  13. Weighting Test Samples in IRT Linking and Equating: Toward an Improved Sampling Design for Complex Equating. Research Report. ETS RR-13-39

    ERIC Educational Resources Information Center

    Qian, Jiahe; Jiang, Yanming; von Davier, Alina A.

    2013-01-01

    Several factors could cause variability in item response theory (IRT) linking and equating procedures, such as the variability across examinee samples and/or test items, seasonality, regional differences, native language diversity, gender, and other demographic variables. Hence, the following question arises: Is it possible to select optimal…

  14. Sci—Thur AM: YIS - 03: irtGPUMCD: a new GPU-calculated dosimetry code for {sup 177}Lu-octreotate radionuclide therapy of neuroendocrine tumors

    SciTech Connect

    Montégiani, Jean-François; Gaudin, Émilie; Després, Philippe; Jackson, Price A.; Beauregard, Jean-Mathieu

    2014-08-15

    In peptide receptor radionuclide therapy (PRRT), huge inter-patient variability in absorbed radiation doses per administered activity mandates the utilization of individualized dosimetry to evaluate therapeutic efficacy and toxicity. We created a reliable GPU-calculated dosimetry code (irtGPUMCD) and assessed {sup 177}Lu-octreotate renal dosimetry in eight patients (4 cycles of approximately 7.4 GBq). irtGPUMCD was derived from a brachytherapy dosimetry code (bGPUMCD), which was adapted to {sup 177}Lu PRRT dosimetry. Serial quantitative single-photon emission computed tomography (SPECT) images were obtained from three SPECT/CT acquisitions performed at 4, 24 and 72 hours after {sup 177}Lu-octreotate administration, and registered with non-rigid deformation of CT volumes, to obtain {sup 177}Lu-octreotate 4D quantitative biodistribution. Local energy deposition from the β disintegrations was assumed. Using Monte Carlo gamma photon transportation, irtGPUMCD computed dose rate at each time point. Average kidney absorbed dose was obtained from 1-cm{sup 3} VOI dose rate samples on each cortex, subjected to a biexponential curve fit. Integration of the latter time-dose rate curve yielded the renal absorbed dose. The mean renal dose per administered activity was 0.48 ± 0.13 Gy/GBq (range: 0.30–0.71 Gy/GBq). Comparison to another PRRT dosimetry code (VRAK: Voxelized Registration and Kinetics) showed fair accordance with irtGPUMCD (11.4 ± 6.8 %, range: 3.3–26.2%). These results suggest the possibility to use the irtGPUMCD code in order to personalize administered activity in PRRT. This could allow improving clinical outcomes by maximizing per-cycle tumor doses, without exceeding the tolerable renal dose.

  15. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    PubMed Central

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1−xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

  16. Log-Multiplicative Association Models as Item Response Models

    ERIC Educational Resources Information Center

    Anderson, Carolyn J.; Yu, Hsiu-Ting

    2007-01-01

    Log-multiplicative association (LMA) models, which are special cases of log-linear models, have interpretations in terms of latent continuous variables. Two theoretical derivations of LMA models based on item response theory (IRT) arguments are presented. First, we show that Anderson and colleagues (Anderson & Vermunt, 2000; Anderson & Bockenholt,…

  17. Generalizability in Item Response Modeling

    ERIC Educational Resources Information Center

    Briggs, Derek C.; Wilson, Mark

    2007-01-01

    An approach called generalizability in item response modeling (GIRM) is introduced in this article. The GIRM approach essentially incorporates the sampling model of generalizability theory (GT) into the scaling model of item response theory (IRT) by making distributional assumptions about the relevant measurement facets. By specifying a random…

  18. Modeling and simulation of bone mineral density response from a phase 2 study of ONO-5334, a new cathepsin K inhibitor, to support dose selection in osteoporosis.

    PubMed

    Hasegawa, Chihiro; Kastrissios, Helen; Monteleone, Jonathan; Ohno, Tomoya; Umemura, Takeo; Ohyama, Michiyo; Nagase, Shinichi; Small, Maria; Deacon, Steve; Ogawa, Mikio; Ieiri, Ichiro

    2014-08-01

    ONO-5334, a selective inhibitor of cathepsin K, is a potential new treatment for osteoporosis. The objectives of this modeling study were to (1) develop exposure-response (E-R) models to relate ONO-5334 exposure to bone mineral density (BMD), (2) predict BMD responses to various doses of ONO-5334 for both immediate release tablet (IRT) and sustained release tablet (SRT) formulations where only BMD response after administration of IRT had been studied to date, (3) inform selection of appropriate formulation/dose using simulation for future clinical trials. A population pharmacokinetic (PK) model was developed to simultaneously analyze data for both IRT and SRT. The exposure metrics at steady state were estimated by post hoc Bayesian prediction using the final population PK model. E-R models were developed using dose-ranging data with only IRT from postmenopausal females with osteoporosis. Based on the developed model, lumbar spine and total hip BMD after administration of ONO-5334 SRT as well as IRT were simulated. The simulation results showed that ONO-5334 SRT should provide comparable BMD responses at a lower dose relative to IRT (a finding consistent with the results from a previous population PK-PD modeling study with bone resorption markers).

  19. Modeling Diagnostic Assessments with Bayesian Networks

    ERIC Educational Resources Information Center

    Almond, Russell G.; DiBello, Louis V.; Moulder, Brad; Zapata-Rivera, Juan-Diego

    2007-01-01

    This paper defines Bayesian network models and examines their applications to IRT-based cognitive diagnostic modeling. These models are especially suited to building inference engines designed to be synchronous with the finer grained student models that arise in skills diagnostic assessment. Aspects of the theory and use of Bayesian network models…

  20. Cognitive Diagnostic Modeling Using R

    ERIC Educational Resources Information Center

    Ravand, Hamdollah

    2015-01-01

    Cognitive diagnostic models (CDM) have been around for more than a decade but their application is far from widespread for mainly two reasons: (1) CDMs are novel, as compared to traditional IRT models. Consequently, many researchers lack familiarity with them and their properties, and (2) Software programs doing CDMs have been expensive and not…

  1. Metal-binding thermodynamics of the histidine-rich sequence from the metal-transport protein IRT1 of Arabidopsis thaliana.

    PubMed

    Grossoehme, Nicholas E; Akilesh, Shreeram; Guerinot, Mary Lou; Wilcox, Dean E

    2006-10-16

    The widespread ZIP family of transmembrane metal-transporting proteins is characterized by a large intracellular loop that contains a histidine-rich sequence whose biological role is unknown. To provide a chemical basis for this role, we prepared and studied a peptide corresponding to this sequence from the first iron-regulated transporter (IRT1) of Arabidopsis thaliana, which transports Fe2+ as well as Mn2+, Co2+, Zn2+, and Cd2+. Isothermal titration calorimetry (ITC) measurements, which required novel experiments and data analysis, and supporting spectroscopic methods were used to quantify IRT1's metal-binding affinity and associated thermodynamics. The peptide, PHGHGHGHGP, binds metal ions with 1:1 stoichiometry and stabilities that are consistent with the Irving-Williams series. Comparison of the metal-binding thermodynamics of the peptide with those of trien provides new insight about enthalpic and entropic contributions to the stability of the metal-peptide complex. Although Fe2+ and other IRT1-transported metal ions do not bind very tightly, this His-rich sequence has a very high entropy-driven affinity for Fe3+, which may have biological significance.

  2. The effect of emissive biased limiter on the magnetohydrodynamic modes in the IR-T1 tokamak

    SciTech Connect

    Ghasemloo, M.; Ghoranneviss, M.; Salem, M. K.; Arvin, R.; Mohammadi, S.; Nik Mohammadi, A.

    2013-03-15

    A moveable emissive biased limiter (EBL) for the investigation of spatial and temporal structure of MHD modes in IR-T1 tokamak, based on mirnov oscillations, was designed and constructed. The biasing has been considered to improve the global confinement by setting up an electric field at the plasma edge. Radial electric field (E{sub r}) modifies edge plasma turbulence, plasma rotation, and transport. Mirnov oscillations using singular value decomposition (SVD) and wavelet techniques were analyzed. SVD algorithm has been employed to analyze the frequency and wavenumber harmonics of the MHD fluctuations. The time-resolved frequency component analysis has been performed using wavelets. The EBL was applied to plasma at 10 ms with negative polarity. The results show that after applying EBL, the m = 2 mode is grown, m = 3 mode is suppressed, and H{sub {alpha}} radiation is decreased. Furthermore, results of the wavelet analysis of mirnov coil in the time range of 8-12 ms indicate that 1.5 ms after applying EBL, the MHD frequency is reduced from 45 kHz to 25 kHz.

  3. Identification of the 1PL Model with Guessing Parameter: Parametric and Semi-Parametric Results

    ERIC Educational Resources Information Center

    San Martin, Ernesto; Rolin, Jean-Marie; Castro, Luis M.

    2013-01-01

    In this paper, we study the identification of a particular case of the 3PL model, namely when the discrimination parameters are all constant and equal to 1. We term this model, 1PL-G model. The identification analysis is performed under three different specifications. The first specification considers the abilities as unknown parameters. It is…

  4. Modeling Math Growth Trajectory--An Application of Conventional Growth Curve Model and Growth Mixture Model to ECLS K-5 Data

    ERIC Educational Resources Information Center

    Lu, Yi

    2016-01-01

    To model students' math growth trajectory, three conventional growth curve models and three growth mixture models are applied to the Early Childhood Longitudinal Study Kindergarten-Fifth grade (ECLS K-5) dataset in this study. The results of conventional growth curve model show gender differences on math IRT scores. When holding socio-economic…

  5. A modular approach for item response theory modeling with the R package flirt.

    PubMed

    Jeon, Minjeong; Rijmen, Frank

    2016-06-01

    The new R package flirt is introduced for flexible item response theory (IRT) modeling of psychological, educational, and behavior assessment data. flirt integrates a generalized linear and nonlinear mixed modeling framework with graphical model theory. The graphical model framework allows for efficient maximum likelihood estimation. The key feature of flirt is its modular approach to facilitate convenient and flexible model specifications. Researchers can construct customized IRT models by simply selecting various modeling modules, such as parametric forms, number of dimensions, item and person covariates, person groups, link functions, etc. In this paper, we describe major features of flirt and provide examples to illustrate how flirt works in practice.

  6. Conditional Standard Errors, Reliability and Decision Consistency of Performance Levels Using Polytomous IRT.

    ERIC Educational Resources Information Center

    Wang, Tianyou; And Others

    M. J. Kolen, B. A. Hanson, and R. L. Brennan (1992) presented a procedure for assessing the conditional standard error of measurement (CSEM) of scale scores using a strong true-score model. They also investigated the ways of using nonlinear transformation from number-correct raw score to scale score to equalize the conditional standard error along…

  7. Modeling Rule-Based Item Generation

    ERIC Educational Resources Information Center

    Geerlings, Hanneke; Glas, Cees A. W.; van der Linden, Wim J.

    2011-01-01

    An application of a hierarchical IRT model for items in families generated through the application of different combinations of design rules is discussed. Within the families, the items are assumed to differ only in surface features. The parameters of the model are estimated in a Bayesian framework, using a data-augmented Gibbs sampler. An obvious…

  8. Modeling Nonignorable Missing Data in Speeded Tests

    ERIC Educational Resources Information Center

    Glas, Cees A. W.; Pimentel, Jonald L.

    2008-01-01

    In tests with time limits, items at the end are often not reached. Usually, the pattern of missing responses depends on the ability level of the respondents; therefore, missing data are not ignorable in statistical inference. This study models data using a combination of two item response theory (IRT) models: one for the observed response data and…

  9. μSR and magnetometry study of superconducting 5% Pt-doped IrTe2

    DOE PAGES

    Wilson, M. N.; Medina, T.; Munsie, T. J.; ...

    2016-11-11

    In this paper, we present magnetometry and muon spin rotation ( SR) measurements of the superconducting dichalcogenide Ir0.95Pt0.05Te2. From both sets of measurements we calculate the penetration depth and thence superfluid density as a function of temperature. The temperature dependence of the superfluid densities from both sets of data indicate fully gapped superconductivity that can be fit to a conventional s-wave model and yield fitting parameters consistent with a BCS weak coupling superconductor. Finally, we therefore see no evidence for exotic superconductivity in Ir0.95Pt0.05Te2.

  10. Bayesian Prior Choice in IRT Estimation Using MCMC and Variational Bayes

    PubMed Central

    Natesan, Prathiba; Nandakumar, Ratna; Minka, Tom; Rubright, Jonathan D.

    2016-01-01

    This study investigated the impact of three prior distributions: matched, standard vague, and hierarchical in Bayesian estimation parameter recovery in two and one parameter models. Two Bayesian estimation methods were utilized: Markov chain Monte Carlo (MCMC) and the relatively new, Variational Bayesian (VB). Conditional (CML) and Marginal Maximum Likelihood (MML) estimates were used as baseline methods for comparison. Vague priors produced large errors or convergence issues and are not recommended. For both MCMC and VB, the hierarchical and matched priors showed the lowest root mean squared errors (RMSEs) for ability estimates; RMSEs of difficulty estimates were similar across estimation methods. For the standard errors (SEs), MCMC-hierarchical displayed the largest values across most conditions. SEs from the VB estimation were among the lowest in all but one case. Overall, VB-hierarchical, VB-matched, and MCMC-matched performed best. VB with hierarchical priors are recommended in terms of their accuracy, and cost and (subsequently) time effectiveness. PMID:27729878

  11. Radiation protection, radioactive waste management and site monitoring at the nuclear scientific experimental and educational centre IRT-Sofia at INRNE-BAS.

    PubMed

    Mladenov, Al; Stankov, D; Nonova, Tz; Krezhov, K

    2014-11-01

    This article identifies important components and describes the safe practices in implementing radiation protection and radioactive waste management programmes, and in their optimisation at the Nuclear Scientific Experimental and Educational Centre with research reactor IRT at INRNE-BAS. It covers the instrumentation and personal protective equipment and organisational issues related to the continuous site monitoring. The reactor is under major reconstruction and the measures applied to radiation monitoring of environment and working area focused on restricting the radiation exposure of the staff as well as compliance with international good practices related to the environmental and public radiation safety requirements are also addressed.

  12. Graded Response Model Based on the Logistic Positive Exponent Family of Models for Dichotomous Responses

    ERIC Educational Resources Information Center

    Samejima, Fumiko

    2008-01-01

    Samejima ("Psychometrika "65:319--335, 2000) proposed the logistic positive exponent family of models (LPEF) for dichotomous responses in the unidimensional latent space. The objective of the present paper is to propose and discuss a graded response model that is expanded from the LPEF, in the context of item response theory (IRT). This…

  13. Assessing Model Data Fit of Unidimensional Item Response Theory Models in Simulated Data

    ERIC Educational Resources Information Center

    Kose, Ibrahim Alper

    2014-01-01

    The purpose of this paper is to give an example of how to assess the model-data fit of unidimensional IRT models in simulated data. Also, the present research aims to explain the importance of fit and the consequences of misfit by using simulated data sets. Responses of 1000 examinees to a dichotomously scoring 20 item test were simulated with 25…

  14. Analysis test of understanding of vectors with the three-parameter logistic model of item response theory and item response curves technique

    NASA Astrophysics Data System (ADS)

    Rakkapao, Suttida; Prasitpong, Singha; Arayathanitkul, Kwan

    2016-12-01

    This study investigated the multiple-choice test of understanding of vectors (TUV), by applying item response theory (IRT). The difficulty, discriminatory, and guessing parameters of the TUV items were fit with the three-parameter logistic model of IRT, using the parscale program. The TUV ability is an ability parameter, here estimated assuming unidimensionality and local independence. Moreover, all distractors of the TUV were analyzed from item response curves (IRC) that represent simplified IRT. Data were gathered on 2392 science and engineering freshmen, from three universities in Thailand. The results revealed IRT analysis to be useful in assessing the test since its item parameters are independent of the ability parameters. The IRT framework reveals item-level information, and indicates appropriate ability ranges for the test. Moreover, the IRC analysis can be used to assess the effectiveness of the test's distractors. Both IRT and IRC approaches reveal test characteristics beyond those revealed by the classical analysis methods of tests. Test developers can apply these methods to diagnose and evaluate the features of items at various ability levels of test takers.

  15. Infrared thermography for CFRP inspection: computational model and experimental results

    NASA Astrophysics Data System (ADS)

    Fernandes, Henrique C.; Zhang, Hai; Morioka, Karen; Ibarra-Castanedo, Clemente; López, Fernando; Maldague, Xavier P. V.; Tarpani, José R.

    2016-05-01

    Infrared Thermography (IRT) is a well-known Non-destructive Testing (NDT) technique. In the last decades, it has been widely applied in several fields including inspection of composite materials (CM), specially the fiber-reinforced polymer matrix ones. Consequently, it is important to develop and improve efficient NDT techniques to inspect and assess the quality of CM parts in order to warranty airworthiness and, at the same time, reduce costs of airline companies. In this paper, active IRT is used to inspect carbon fiber-reinforced polymer (CFRP) at laminate with artificial inserts (built-in sample) placed on different layers prior to the manufacture. Two optical active IRT are used. The first is pulsed thermography (PT) which is the most widely utilized IRT technique. The second is a line-scan thermography (LST) technique: a dynamic technique, which can be employed for the inspection of materials by heating a component, line-by-line, while acquiring a series of thermograms with an infrared camera. It is especially suitable for inspection of large parts as well as complex shaped parts. A computational model developed using COMSOL Multiphysics® was used in order to simulate the inspections. Sequences obtained from PT and LST were processed using principal component thermography (PCT) for comparison. Results showed that it is possible to detect insertions of different sizes at different depths using both PT and LST IRT techniques.

  16. Scale Model Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Canacci, Victor A.

    1997-01-01

    NASA Lewis Research Center's Icing Research Tunnel (IRT) is the world's largest refrigerated wind tunnel and one of only three icing wind tunnel facilities in the United States. The IRT was constructed in the 1940's and has been operated continually since it was built. In this facility, natural icing conditions are duplicated to test the effects of inflight icing on actual aircraft components as well as on models of airplanes and helicopters. IRT tests have been used successfully to reduce flight test hours for the certification of ice-detection instrumentation and ice protection systems. To ensure that the IRT will remain the world's premier icing facility well into the next century, Lewis is making some renovations and is planning others. These improvements include modernizing the control room, replacing the fan blades with new ones to increase the test section maximum velocity to 430 mph, installing new spray bars to increase the size and uniformity of the artificial icing cloud, and replacing the facility heat exchanger. Most of the improvements will have a first-order effect on the IRT's airflow quality. To help us understand these effects and evaluate potential improvements to the flow characteristics of the IRT, we built a modular 1/10th-scale aerodynamic model of the facility. This closed-loop scale-model pilot tunnel was fabricated onsite in the various shops of Lewis' Fabrication Support Division. The tunnel's rectangular sections are composed of acrylic walls supported by an aluminum angle framework. Its turning vanes are made of tubing machined to the contour of the IRT turning vanes. The fan leg of the tunnel, which transitions from rectangular to circular and back to rectangular cross sections, is fabricated of fiberglass sections. The contraction section of the tunnel is constructed from sheet aluminum. A 12-bladed aluminum fan is coupled to a turbine powered by high-pressure air capable of driving the maximum test section velocity to 550 ft

  17. Stochastic Approximation Methods for Latent Regression Item Response Models

    ERIC Educational Resources Information Center

    von Davier, Matthias; Sinharay, Sandip

    2010-01-01

    This article presents an application of a stochastic approximation expectation maximization (EM) algorithm using a Metropolis-Hastings (MH) sampler to estimate the parameters of an item response latent regression model. Latent regression item response models are extensions of item response theory (IRT) to a latent variable model with covariates…

  18. The Philosophical Aspects of IRT Equating: Modeling Drift to Evaluate Cohort Growth in Large-Scale Assessments

    ERIC Educational Resources Information Center

    Taherbhai, Husein; Seo, Daeryong

    2013-01-01

    Calibration and equating is the quintessential necessity for most large-scale educational assessments. However, there are instances when no consideration is given to the equating process in terms of context and substantive realization, and the methods used in its execution. In the view of the authors, equating is not merely an exhibit of the…

  19. FACTOR 9.2: A Comprehensive Program for Fitting Exploratory and Semiconfirmatory Factor Analysis and IRT Models

    ERIC Educational Resources Information Center

    Lorenzo-Seva, Urbano; Ferrando, Pere J.

    2013-01-01

    FACTOR 9.2 was developed for three reasons. First, exploratory factor analysis (FA) is still an active field of research although most recent developments have not been incorporated into available programs. Second, there is now renewed interest in semiconfirmatory (SC) solutions as suitable approaches to the complex structures are commonly found…

  20. Flow Quality Measurements in an Aerodynamic Model of NASA Lewis' Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Canacci, Victor A.; Gonsalez, Jose C.

    1999-01-01

    As part of an ongoing effort to improve the aerodynamic flow characteristics of the Icing Research Tunnel (IRT), a modular scale model of the facility was fabricated. This 1/10th-scale model was used to gain further understanding of the flow characteristics in the IRT. The model was outfitted with instrumentation and data acquisition systems to determine pressures, velocities, and flow angles in the settling chamber and test section. Parametric flow quality studies involving the insertion and removal of a model of the IRT's distinctive heat exchanger (cooler) and/or of a honeycomb in the settling chamber were performed. These experiments illustrate the resulting improvement or degradation in flow quality.

  1. Determination of neutron flux density distribution in the core with LEU fuel IRT-4M at the training reactor VR-1

    SciTech Connect

    Huml, O.

    2008-07-15

    The objective of this work was to determine the neutron flux density distribution in various places of the training reactor VR-1 Sparrow. This experiment was performed on the new core design C1, composed of the new low-enriched uranium fuel cells IRT-4M (19.7 %). This fuel replaced the old high-enriched uranium fuel IRT-3M (36 %) within the framework of the RERTR Program in September 2005. The measurement used the neutron activation analysis method with gold wires. The principle of this method consists in neutron capture in a nucleus of the material forming the activation detector. This capture can change the nucleus in a radioisotope, whose activity can be measured. The absorption cross-section values were evaluated by MCNP computer code. The gold wires were irradiated in seven different positions in the core C1. All irradiations were performed at reactor power level 1E8 (1 kW{sub therm}). The activity of segments of irradiated wires was measured by special automatic device called 'Drat' (Wire in English). (author)

  2. On the Performance Characteristics of Latent-Factor and Knowledge Tracing Models

    ERIC Educational Resources Information Center

    Klingler, Severin; Käser, Tanja; Solenthaler, Barbara; Gross, Markus

    2015-01-01

    Modeling student knowledge is a fundamental task of an intelligent tutoring system. A popular approach for modeling the acquisition of knowledge is Bayesian Knowledge Tracing (BKT). Various extensions to the original BKT model have been proposed, among them two novel models that unify BKT and Item Response Theory (IRT). Latent Factor Knowledge…

  3. A Comparison of Teacher Effectiveness Measures Calculated Using Three Multilevel Models for Raters Effects

    ERIC Educational Resources Information Center

    Murphy, Daniel L.; Beretvas, S. Natasha

    2015-01-01

    This study examines the use of cross-classified random effects models (CCrem) and cross-classified multiple membership random effects models (CCMMrem) to model rater bias and estimate teacher effectiveness. Effect estimates are compared using CTT versus item response theory (IRT) scaling methods and three models (i.e., conventional multilevel…

  4. The Impact of Varied Discrimination Parameters on Mixed-Format Item Response Theory Model Selection

    ERIC Educational Resources Information Center

    Whittaker, Tiffany A.; Chang, Wanchen; Dodd, Barbara G.

    2013-01-01

    Whittaker, Chang, and Dodd compared the performance of model selection criteria when selecting among mixed-format IRT models and found that the criteria did not perform adequately when selecting the more parameterized models. It was suggested by M. S. Johnson that the problems when selecting the more parameterized models may be because of the low…

  5. Minimax D-Optimal Designs for Item Response Theory Models.

    ERIC Educational Resources Information Center

    Berger, Martjin P. F.; King, C. Y. Joy; Wong, Weng Kee

    2000-01-01

    Proposed minimax designs for item response theory (IRT) models to overcome the problem of local optimality. Compared minimax designs to sequentially constructed designs for the two parameter logistic model. Results show that minimax designs can be nearly as efficient as sequentially constructed designs. (Author/SLD)

  6. Cognitive Psychology Meets Psychometric Theory: On the Relation between Process Models for Decision Making and Latent Variable Models for Individual Differences

    ERIC Educational Resources Information Center

    van der Maas, Han L. J.; Molenaar, Dylan; Maris, Gunter; Kievit, Rogier A.; Borsboom, Denny

    2011-01-01

    This article analyzes latent variable models from a cognitive psychology perspective. We start by discussing work by Tuerlinckx and De Boeck (2005), who proved that a diffusion model for 2-choice response processes entails a 2-parameter logistic item response theory (IRT) model for individual differences in the response data. Following this line…

  7. Modified Likelihood-Based Item Fit Statistics for the Generalized Graded Unfolding Model

    ERIC Educational Resources Information Center

    Roberts, James S.

    2008-01-01

    Orlando and Thissen (2000) developed an item fit statistic for binary item response theory (IRT) models known as S-X[superscript 2]. This article generalizes their statistic to polytomous unfolding models. Four alternative formulations of S-X[superscript 2] are developed for the generalized graded unfolding model (GGUM). The GGUM is a…

  8. Exploring the Full-Information Bifactor Model in Vertical Scaling with Construct Shift

    ERIC Educational Resources Information Center

    Li, Ying; Lissitz, Robert W.

    2012-01-01

    To address the lack of attention to construct shift in item response theory (IRT) vertical scaling, a multigroup, bifactor model was proposed to model the common dimension for all grades and the grade-specific dimensions. Bifactor model estimation accuracy was evaluated through a simulation study with manipulated factors of percentage of common…

  9. Stochastic Approximation Methods for Latent Regression Item Response Models. Research Report. ETS RR-09-09

    ERIC Educational Resources Information Center

    von Davier, Matthias; Sinharay, Sandip

    2009-01-01

    This paper presents an application of a stochastic approximation EM-algorithm using a Metropolis-Hastings sampler to estimate the parameters of an item response latent regression model. Latent regression models are extensions of item response theory (IRT) to a 2-level latent variable model in which covariates serve as predictors of the…

  10. Using Data Augmentation and Markov Chain Monte Carlo for the Estimation of Unfolding Response Models

    ERIC Educational Resources Information Center

    Johnson, Matthew S.; Junker, Brian W.

    2003-01-01

    Unfolding response models, a class of item response theory (IRT) models that assume a unimodal item response function (IRF), are often used for the measurement of attitudes. Verhelst and Verstralen (1993)and Andrich and Luo (1993) independently developed unfolding response models by relating the observed responses to a more common monotone IRT…

  11. A Bifactor Multidimensional Item Response Theory Model for Differential Item Functioning Analysis on Testlet-Based Items

    ERIC Educational Resources Information Center

    Fukuhara, Hirotaka; Kamata, Akihito

    2011-01-01

    A differential item functioning (DIF) detection method for testlet-based data was proposed and evaluated in this study. The proposed DIF model is an extension of a bifactor multidimensional item response theory (MIRT) model for testlets. Unlike traditional item response theory (IRT) DIF models, the proposed model takes testlet effects into…

  12. Isolation and characterization of human and mouse ZIRTL, a member of the IRT1 family of transporters, mapping within the epidermal differentiation complex.

    PubMed

    Lioumi, M; Ferguson, C A; Sharpe, P T; Freeman, T; Marenholz, I; Mischke, D; Heizmann, C; Ragoussis, J

    1999-12-01

    We report the precise mapping and characterization of ZIRTL (zinc-iron regulated transporter-like) gene, the first mammalian member of an extensive family of divalent metal ion transporters, comprising IRT1 and ZIP1, ZIP2, ZIP3, and ZIP4 in plants and ZRT1 and ZRT2 in yeast. The human gene maps at the telomeric end of the epidermal differentiation complex (EDC), within chromosomal band 1q21, while the mouse gene maps within the mouse EDC, on mouse chromosome 3, between S100A9 and S100A13. The structure of the human gene has been determined, and message was detected in most adult and fetal tissues including the epidermis. The mouse gene is developmentally regulated and found expressed in fetal and adult suprabasal epidermis, osteoblasts, small intestine, and salivary gland.

  13. Item Response Theory Models for Performance Decline during Testing

    ERIC Educational Resources Information Center

    Jin, Kuan-Yu; Wang, Wen-Chung

    2014-01-01

    Sometimes, test-takers may not be able to attempt all items to the best of their ability (with full effort) due to personal factors (e.g., low motivation) or testing conditions (e.g., time limit), resulting in poor performances on certain items, especially those located toward the end of a test. Standard item response theory (IRT) models fail to…

  14. An NCME Instructional Module on Polytomous Item Response Theory Models

    ERIC Educational Resources Information Center

    Penfield, Randall David

    2014-01-01

    A polytomous item is one for which the responses are scored according to three or more categories. Given the increasing use of polytomous items in assessment practices, item response theory (IRT) models specialized for polytomous items are becoming increasingly common. The purpose of this ITEMS module is to provide an accessible overview of…

  15. A Multilevel Testlet Model for Dual Local Dependence

    ERIC Educational Resources Information Center

    Jiao, Hong; Kamata, Akihito; Wang, Shudong; Jin, Ying

    2012-01-01

    The applications of item response theory (IRT) models assume local item independence and that examinees are independent of each other. When a representative sample for psychometric analysis is selected using a cluster sampling method in a testlet-based assessment, both local item dependence and local person dependence are likely to be induced.…

  16. Three Multidimensional Models for Testlet-Based Tests: Formal Relations and an Empirical Comparison. Research Report. ETS RR-09-37

    ERIC Educational Resources Information Center

    Rijmen, Frank

    2009-01-01

    Three multidimensional item response theory (IRT) models for testlet-based tests are described. In the bifactor model (Gibbons & Hedeker, 1992), each item measures a general dimension in addition to a testlet-specific dimension. The testlet model (Bradlow, Wainer, & Wang, 1999) is a bifactor model in which the loadings on the specific dimensions…

  17. A Model-Based Approach to Goodness-of-Fit Evaluation in Item Response Theory

    ERIC Educational Resources Information Center

    Oberski, Daniel L.; Vermunt, Jeroen K.

    2013-01-01

    These authors congratulate Albert Maydeu-Olivares on his lucid and timely overview of goodness-of-fit assessment in IRT models, a field to which he himself has contributed considerably in the form of limited information statistics. In this commentary, Oberski and Vermunt focus on two aspects of model fit: (1) what causes there may be of misfit;…

  18. Generating Dichotomous Item Scores with the Four-Parameter Beta Compound Binomial Model

    ERIC Educational Resources Information Center

    Monahan, Patrick O.; Lee, Won-Chan; Ankenmann, Robert D.

    2007-01-01

    A Monte Carlo simulation technique for generating dichotomous item scores is presented that implements (a) a psychometric model with different explicit assumptions than traditional parametric item response theory (IRT) models, and (b) item characteristic curves without restrictive assumptions concerning mathematical form. The four-parameter beta…

  19. Introduction to Multilevel Item Response Theory Analysis: Descriptive and Explanatory Models

    ERIC Educational Resources Information Center

    Sulis, Isabella; Toland, Michael D.

    2017-01-01

    Item response theory (IRT) models are the main psychometric approach for the development, evaluation, and refinement of multi-item instruments and scaling of latent traits, whereas multilevel models are the primary statistical method when considering the dependence between person responses when primary units (e.g., students) are nested within…

  20. Model Choice and Sample Size in Item Response Theory Analysis of Aphasia Tests

    ERIC Educational Resources Information Center

    Hula, William D.; Fergadiotis, Gerasimos; Martin, Nadine

    2012-01-01

    Purpose: The purpose of this study was to identify the most appropriate item response theory (IRT) measurement model for aphasia tests requiring 2-choice responses and to determine whether small samples are adequate for estimating such models. Method: Pyramids and Palm Trees (Howard & Patterson, 1992) test data that had been collected from…

  1. An Assessment of the Nonparametric Approach for Evaluating the Fit of Item Response Models

    ERIC Educational Resources Information Center

    Liang, Tie; Wells, Craig S.; Hambleton, Ronald K.

    2014-01-01

    As item response theory has been more widely applied, investigating the fit of a parametric model becomes an important part of the measurement process. There is a lack of promising solutions to the detection of model misfit in IRT. Douglas and Cohen introduced a general nonparametric approach, RISE (Root Integrated Squared Error), for detecting…

  2. A Multidimensional Partial Credit Model with Associated Item and Test Statistics: An Application to Mixed-Format Tests

    ERIC Educational Resources Information Center

    Yao, Lihua; Schwarz, Richard D.

    2006-01-01

    Multidimensional item response theory (IRT) models have been proposed for better understanding the dimensional structure of data or to define diagnostic profiles of student learning. A compensatory multidimensional two-parameter partial credit model (M-2PPC) for constructed-response items is presented that is a generalization of those proposed to…

  3. Use of a Scale Model in the Design of Modifications to the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Canacci, Victor A.; Gonsalez, Jose C.; Spera, David A.; Burke, Thomas (Technical Monitor)

    2001-01-01

    Major modifications were made in 1999 to the 6- by 9-Foot (1.8- by 2.7-m) Icing Research tunnel (IRT) at the NASA Glenn Research Center, including replacement of its heat exchanger and associated ducts and turning vanes, and the addition of fan outlet guide vanes (OGV's). A one-tenth scale model of the IRT (designated as the SMIRT) was constructed with and without these modifications and tested to increase confidence in obtaining expected improvements in flow quality around the tunnel loop. The SMIRT is itself an aerodynamic test facility whose flow patterns without modifications have been shown to be accurate, scaled representations of those measured in the IRT prior to the 1999 upgrade program. In addition, tests in the SMIRT equipped with simulated OGV's indicated that these devices in the IRT might reduce flow distortions immediately downstream of the fan by two thirds. Flow quality parameters measured in the SMIRT were projected to the full-size modified IRT, and quantitative estimates of improvements in flow quality were given prior to construction. In this paper, the results of extensive flow quality studies conducted in the SMIRT are documented. Samples of these are then compared with equivalent measurements made in the full-scale IRT, both before and after its configuration was upgraded. Airspeed, turbulence intensity, and flow angularity distributions are presented for cross sections downstream of the drive fan, both upstream and downstream of the replacement flat heat exchanger, in the stilling chamber, in the test section, and in the wakes of the new comer turning vanes with their unique expanding and contracting designs. Lessons learned from these scale-model studies are discussed.

  4. Patient-Reported Outcomes Measurement Information System (PROMIS) Domain Names and Definitions Revisions: Further Evaluation of Content Validity in IRT-derived Item Banks

    PubMed Central

    Riley, William T.; Rothrock, Nan; Bruce, Bonnie; Christodolou, Christopher; Cook, Karon; Hahn, Elizabeth A.; Cella, David

    2013-01-01

    Purpose Content validity of patient-reported outcomes (PROs) is evaluated primarily during item development, but subsequent psychometric analyses, particularly for item-response theory (IRT)-derived scales, often result in considerable item pruning and potential loss of content. After selecting items for the PROMIS banks based on psychometric and content considerations, we invited external content expert reviews of the degree to which the initial domain names and definitions represented the calibrated item bank content. Methods A minimum of four content experts reviewed each item bank and recommended a domain name and definition based on item content. Domain names and definitions then were revealed to the experts who rated how well these names and definitions fit the bank content and provided recommendations for definition revisions. Results These reviews indicated that the PROMIS domain names and definitions remained generally representative of bank content following item pruning, but modifications to two domain names and minor to moderate revisions of all domain definitions were needed to optimize fit with the item bank content. Conclusions This reevaluation of domain names and definitions following psychometric item pruning, although not previously documented in the literature, appears to be an important procedure for refining conceptual frameworks and further supporting content validity. PMID:20593306

  5. A Test of the Need Hierarchy Concept by a Markov Model of Change in Need Strength.

    ERIC Educational Resources Information Center

    Rauschenberger, John; And Others

    1980-01-01

    In this study of 547 high school graduates, Alderfer's and Maslow's need hierarchy theories were expressed in Markov chain form and were subjected to empirical test. Both models were disconfirmed. Corroborative multiwave correlational analysis also failed to support the need hierarchy concept. (Author/IRT)

  6. A Bayesian Approach to Person Fit Analysis in Item Response Theory Models. Research Report.

    ERIC Educational Resources Information Center

    Glas, Cees A. W.; Meijer, Rob R.

    A Bayesian approach to the evaluation of person fit in item response theory (IRT) models is presented. In a posterior predictive check, the observed value on a discrepancy variable is positioned in its posterior distribution. In a Bayesian framework, a Markov Chain Monte Carlo procedure can be used to generate samples of the posterior distribution…

  7. Evaluating the Robustness of Graded Response Model and Classical Test Theory Parameter Estimates to Deviant Items.

    ERIC Educational Resources Information Center

    Sinar, Evan F.; Zickar, Michael J.

    2002-01-01

    Examined the influence of deviant scale items on item parameter estimates of focal scale items and person parameter estimates through a comparison of item response theory (IRT) and classical test theory (CTT) models. Used Monte Carlo methods to explore results from a pilot investigation of job attitude data. Discusses implications for researchers…

  8. The Importance of Positive Self-Concept for Islamic Education Teachers as a Role Model

    ERIC Educational Resources Information Center

    Muhamad, Nurul Asiah Fasehah; Hamzah, Mohd Isa; Tamuri, Ab. Halim; Ja'afar, Noornajihan; Ghazali, Norzulaili Mohd; Amat, Robiatul Adawiyah Mohd; Raus, Norakyairee Mohd; Hassan, Syed Najihuddin Syed

    2013-01-01

    This study embarks from the great and huge responsibility of teachers nowadays especially the IRT (Islamic religious teachers). As the role model of students, they play an important task especially in producing the good Muslim character. Therefore, their job not only focuses on the content of subject but becomes wider in scope, more than other…

  9. Assessing item fit for unidimensional item response theory models using residuals from estimated item response functions.

    PubMed

    Haberman, Shelby J; Sinharay, Sandip; Chon, Kyong Hee

    2013-07-01

    Residual analysis (e.g. Hambleton & Swaminathan, Item response theory: principles and applications, Kluwer Academic, Boston, 1985; Hambleton, Swaminathan, & Rogers, Fundamentals of item response theory, Sage, Newbury Park, 1991) is a popular method to assess fit of item response theory (IRT) models. We suggest a form of residual analysis that may be applied to assess item fit for unidimensional IRT models. The residual analysis consists of a comparison of the maximum-likelihood estimate of the item characteristic curve with an alternative ratio estimate of the item characteristic curve. The large sample distribution of the residual is proved to be standardized normal when the IRT model fits the data. We compare the performance of our suggested residual to the standardized residual of Hambleton et al. (Fundamentals of item response theory, Sage, Newbury Park, 1991) in a detailed simulation study. We then calculate our suggested residuals using data from an operational test. The residuals appear to be useful in assessing the item fit for unidimensional IRT models.

  10. Item Response Theory Models for Wording Effects in Mixed-Format Scales

    ERIC Educational Resources Information Center

    Wang, Wen-Chung; Chen, Hui-Fang; Jin, Kuan-Yu

    2015-01-01

    Many scales contain both positively and negatively worded items. Reverse recoding of negatively worded items might not be enough for them to function as positively worded items do. In this study, we commented on the drawbacks of existing approaches to wording effect in mixed-format scales and used bi-factor item response theory (IRT) models to…

  11. A New Statistic for Evaluating Item Response Theory Models for Ordinal Data. CRESST Report 839

    ERIC Educational Resources Information Center

    Cai, Li; Monroe, Scott

    2014-01-01

    We propose a new limited-information goodness of fit test statistic C[subscript 2] for ordinal IRT models. The construction of the new statistic lies formally between the M[subscript 2] statistic of Maydeu-Olivares and Joe (2006), which utilizes first and second order marginal probabilities, and the M*[subscript 2] statistic of Cai and Hansen…

  12. A Practical Computer Adaptive Testing Model for Small-Scale Scenarios

    ERIC Educational Resources Information Center

    Tao, Yu-Hui; Wu, Yu-Lung; Chang, Hsin-Yi

    2008-01-01

    Computer adaptive testing (CAT) is theoretically sound and efficient, and is commonly seen in larger testing programs. It is, however, rarely seen in a smaller-scale scenario, such as in classrooms or business daily routines, because of the complexity of most adopted Item Response Theory (IRT) models. While the Sequential Probability Ratio Test…

  13. Satisfaction Ratings of QOLPAV: Psychometric Properties Based on the Graded Response Model

    ERIC Educational Resources Information Center

    Chen, Ssu-Kuang; Hwang, Fang-Ming; Lin, Sunny S. J.

    2013-01-01

    A scale measuring quality of life (QOL) is important in adolescent research. Using the graded response model (GRM), this study evaluates the psychometric properties of the satisfaction ratings of the Quality of Life Profile Adolescent Version (QOLPAV). Data for 1,392 adolescents were used to check IRT assumptions such as unidimensionality and…

  14. Parent Ratings of ADHD Symptoms: Generalized Partial Credit Model Analysis of Differential Item Functioning across Gender

    ERIC Educational Resources Information Center

    Gomez, Rapson

    2012-01-01

    Objective: Generalized partial credit model, which is based on item response theory (IRT), was used to test differential item functioning (DIF) for the "Diagnostic and Statistical Manual of Mental Disorders" (4th ed.), inattention (IA), and hyperactivity/impulsivity (HI) symptoms across boys and girls. Method: To accomplish this, parents completed…

  15. Firestar-"D": Computerized Adaptive Testing Simulation Program for Dichotomous Item Response Theory Models

    ERIC Educational Resources Information Center

    Choi, Seung W.; Podrabsky, Tracy; McKinney, Natalie

    2012-01-01

    Computerized adaptive testing (CAT) enables efficient and flexible measurement of latent constructs. The majority of educational and cognitive measurement constructs are based on dichotomous item response theory (IRT) models. An integral part of developing various components of a CAT system is conducting simulations using both known and empirical…

  16. Fit of Item Response Theory Models: A Survey of Data from Several Operational Tests. Research Report. ETS RR-11-29

    ERIC Educational Resources Information Center

    Sinharay, Sandip; Haberman, Shelby J.; Jia, Helena

    2011-01-01

    Standard 3.9 of the "Standards for Educational and Psychological Testing" (American Educational Research Association, American Psychological Association, & National Council for Measurement in Education, 1999) demands evidence of model fit when an item response theory (IRT) model is used to make inferences from a data set. We applied two recently…

  17. IRT-Based Measurement of Short-Term Changes of Ability, with an Application to Assessing the "Mozart Effect"

    ERIC Educational Resources Information Center

    Gittler, Georg; Fischer, Gerhard

    2011-01-01

    The article extends and applies previous approaches by Klauer and Fischer to the statistical evaluation of ability changes in tests conforming to the Rasch model (RM). Exact uniformly most powerful unbiased (UMPU) hypothesis tests and uniformly most accurate (UMA) confidence intervals (CIs) for the amount of change can be constructed for each…

  18. A Comparison of Item Response Theory and Observed Score DIF Detection Measures for the Graded Response Model.

    ERIC Educational Resources Information Center

    Cohen, Allan S.; Kim, Seock-Ho; Wollack, James A.

    This paper provides a review of procedures for detection of differential item functioning (DIF) for item response theory (IRT) and observed score methods for the graded response model. In addition, data from a test anxiety scale were analyzed to examine the congruence among these procedures. Data from Nasser, Takahashi, and Benson (1997) were…

  19. A Comparison of Item Parameter Standard Error Estimation Procedures for Unidimensional and Multidimensional Item Response Theory Modeling

    ERIC Educational Resources Information Center

    Paek, Insu; Cai, Li

    2014-01-01

    The present study was motivated by the recognition that standard errors (SEs) of item response theory (IRT) model parameters are often of immediate interest to practitioners and that there is currently a lack of comparative research on different SE (or error variance-covariance matrix) estimation procedures. The present study investigated item…

  20. A Mixture Rasch Model with a Covariate: A Simulation Study via Bayesian Markov Chain Monte Carlo Estimation

    ERIC Educational Resources Information Center

    Dai, Yunyun

    2013-01-01

    Mixtures of item response theory (IRT) models have been proposed as a technique to explore response patterns in test data related to cognitive strategies, instructional sensitivity, and differential item functioning (DIF). Estimation proves challenging due to difficulties in identification and questions of effect size needed to recover underlying…

  1. Numerical Differentiation Methods for Computing Error Covariance Matrices in Item Response Theory Modeling: An Evaluation and a New Proposal

    ERIC Educational Resources Information Center

    Tian, Wei; Cai, Li; Thissen, David; Xin, Tao

    2013-01-01

    In item response theory (IRT) modeling, the item parameter error covariance matrix plays a critical role in statistical inference procedures. When item parameters are estimated using the EM algorithm, the parameter error covariance matrix is not an automatic by-product of item calibration. Cai proposed the use of Supplemented EM algorithm for…

  2. A Study of Confidence and Accuracy Using the Rasch Modeling Procedures. Research Report. ETS RR-08-42

    ERIC Educational Resources Information Center

    Paek, Insu; Lee, Jihyun; Stankov, Lazar; Wilson, Mark

    2008-01-01

    This study investigated the relationship between students' actual performance (accuracy) and their subjective judgments of accuracy (confidence) on selected English language proficiency tests. The unidimensional and multidimensional IRT Rasch approaches were used to model the discrepancy between confidence and accuracy at the item and test level…

  3. The Meaning of Goodness-of-Fit Tests: Commentary on "Goodness-of-Fit Assessment of Item Response Theory Models"

    ERIC Educational Resources Information Center

    Thissen, David

    2013-01-01

    In this commentary, David Thissen states that "Goodness-of-fit assessment for IRT models is maturing; it has come a long way from zero." Thissen then references prior works on "goodness of fit" in the index of Lord and Novick's (1968) classic text; Yen (1984); Drasgow, Levine, Tsien, Williams, and Mead (1995); Chen and…

  4. An Item Response Theory (IRT) analysis of the Short Inventory of Problems-Alcohol and Drugs (SIP-AD) among non-treatment seeking men-who-have-sex-with-men: evidence for a shortened 10-item SIP-AD.

    PubMed

    Hagman, Brett T; Kuerbis, Alexis N; Morgenstern, Jon; Bux, Donald A; Parsons, Jeffrey T; Heidinger, Bram E

    2009-11-01

    The Short Inventory of Problems-Alcohol and Drugs (SIP-AD) is a 15-item measure that assesses concurrently negative consequences associated with alcohol and illicit drug use. Current psychometric evaluation has been limited to classical test theory (CTT) statistics, and it has not been validated among non-treatment seeking men-who-have-sex-with-men (MSM). Methods from Item Response Theory (IRT) can improve upon CTT by providing an in-depth analysis of how each item performs across the underlying latent trait that it is purported to measure. The present study examined the psychometric properties of the SIP-AD using methods from both IRT and CTT among a non-treatment seeking MSM sample (N=469). Participants were recruited from the New York City area and were asked to participate in a series of studies examining club drug use. Results indicated that five items on the SIP-AD demonstrated poor item misfit or significant differential item functioning (DIF) across race/ethnicity and HIV status. These five items were dropped and two-parameter IRT analyses were conducted on the remaining 10 items, which indicated a restricted range of item location parameters (-.15 to -.99) plotted at the lower end of the latent negative consequences severity continuum, and reasonably high discrimination parameters (1.30 to 2.22). Additional CTT statistics were compared between the original 15-item SIP-AD and the refined 10-item SIP-AD and suggest that the differences were negligible with the refined 10-item SIP-AD indicating a high degree of reliability and validity. Findings suggest the SIP-AD can be shortened to 10 items and appears to be a non-biased reliable and valid measure among non-treatment seeking MSM.

  5. An Item Response Theory (IRT) Analysis of the Short Inventory of Problems-Alcohol and Drugs (SIP-AD) among non-treatment seeking Men-Who-Have-Sex-With-Men: Evidence for a shortened 10-item SIP-AD

    PubMed Central

    Hagman, Brett T.; Kuerbis, Alexis N.; Morgenstern, Jon; Bux, Donald A.; Parsons, Jeffrey T.; Heidinger, Bram E.

    2009-01-01

    The Short Inventory of Problems-Alcohol and Drugs (SIP-AD) is a 15-item measure that assesses concurrently negative consequences associated with alcohol and illicit drug use. Current psychometric evaluation has been limited to classical test theory (CTT) statistics, and it has not been validated among non-treatment seeking men-who-have-sex-with-men (MSM). Methods from Item Response Theory (IRT) can improve upon CTT by providing an in-depth analysis of how each item performs across the underlying latent trait that it is purported to measure. The present study examined the psychometric properties of the SIP-AD using methods from both IRT and CTT among a non-treatment seeking MSM sample (N = 469). Participants were recruited from the New York City area and were asked to participate in a series of studies examining club drug use. Results indicated that five items on the SIP-AD demonstrated poor item misfit or significant differential item functioning (DIF) across race/ethnicity and HIV status. These five items were dropped and two-parameter IRT analyses were conducted on the remaining 10 items, which indicated a restricted range of item location parameters (−.15 to −.99) plotted at the lower end of the latent negative consequences severity continuum, and reasonably high discrimination parameters (1.30 to 2.22). Additional CTT statistics were compared between the original 15-item SIP-AD and the refined 10-item SIP-AD and suggest that the differences were negligible with the refined 10-item SIP-AD indicating a high degree of reliability and validity. Findings suggest the SIP-AD can be shortened to 10 items and appears to be a non-biased reliable and valid measure among non-treatment seeking MSM. PMID:19564078

  6. Estimation of Standard Error of Regression Effects in Latent Regression Models Using Binder's Linearization. Research Report. ETS RR-07-09

    ERIC Educational Resources Information Center

    Li, Deping; Oranje, Andreas

    2007-01-01

    Two versions of a general method for approximating standard error of regression effect estimates within an IRT-based latent regression model are compared. The general method is based on Binder's (1983) approach, accounting for complex samples and finite populations by Taylor series linearization. In contrast, the current National Assessment of…

  7. Spectral Analysis and Experimental Modeling of Ice Accretion Roughness

    NASA Technical Reports Server (NTRS)

    Orr, D. J.; Breuer, K. S.; Torres, B. E.; Hansman, R. J., Jr.

    1996-01-01

    A self-consistent scheme for relating wind tunnel ice accretion roughness to the resulting enhancement of heat transfer is described. First, a spectral technique of quantitative analysis of early ice roughness images is reviewed. The image processing scheme uses a spectral estimation technique (SET) which extracts physically descriptive parameters by comparing scan lines from the experimentally-obtained accretion images to a prescribed test function. Analysis using this technique for both streamwise and spanwise directions of data from the NASA Lewis Icing Research Tunnel (IRT) are presented. An experimental technique is then presented for constructing physical roughness models suitable for wind tunnel testing that match the SET parameters extracted from the IRT images. The icing castings and modeled roughness are tested for enhancement of boundary layer heat transfer using infrared techniques in a "dry" wind tunnel.

  8. Investigating Separate and Concurrent Approaches for Item Parameter Drift in 3PL Item Response Theory Equating

    ERIC Educational Resources Information Center

    Arce-Ferrer, Alvaro J.; Bulut, Okan

    2017-01-01

    This study examines separate and concurrent approaches to combine the detection of item parameter drift (IPD) and the estimation of scale transformation coefficients in the context of the common item nonequivalent groups design with the three-parameter item response theory equating. The study uses real and synthetic data sets to compare the two…

  9. An Introduction to the DA-T Gibbs Sampler for the Two-Parameter Logistic (2PL) Model and beyond

    ERIC Educational Resources Information Center

    Maris, Gunter; Bechger, Timo M.

    2005-01-01

    The DA-T Gibbs sampler is proposed by Maris and Maris (2002) as a Bayesian estimation method for a wide variety of "Item Response Theory (IRT) models". The present paper provides an expository account of the DA-T Gibbs sampler for the 2PL model. However, the scope is not limited to the 2PL model. It is demonstrated how the DA-T Gibbs…

  10. Pharmacokinetic/pharmacodynamic modeling of antipyretic and anti-inflammatory effects of naproxen in the rat.

    PubMed

    Josa, M; Urizar, J P; Rapado, J; Dios-Viéitez, C; Castañeda-Hernández, G; Flores-Murrieta, F; Renedo, M J; Trocóniz, I F

    2001-04-01

    Pharmacokinetic/pharmacodynamic modeling was used to characterize the antipyretic and anti-inflammatory effects of naproxen in rats. An indirect response model was used to describe the antipyretic effects of naproxen after short intravenous infusions. The model assumes that basal temperature (T(a)) is maintained by the balance of fever mediators given by a constant (zero order) rate of synthesis (K(syn)), and a first order rate of degradation (K(out)). After an intraperitoneal injection of lipopolysaccharide, the change in T(a) was modeled assuming an increase in fever mediators described as an input rate function [IR(t)] estimated nonparametrically. An inhibitory E(max) model adequately described the inhibition of IR(t) by naproxen. A more complex model was used to describe the anti-inflammatory response of oral naproxen in the carrageenin-induced edema model. Before carrageenin injection, physiological conditions are maintained by a balance of inflammation mediators given by K(syn) and K(out) (see above). After carrageenin injection, the additional synthesis of mediators is described by IR(t) (see above). Such mediators induced an inflammatory process, which is governed by a first order rate constant (K(IN)) that can be inhibited by the presence of naproxen in plasma. The sigmoidal E(max) model also well described the inhibition of K(IN) by naproxen. Estimates for IC(50) [concentration of naproxen in plasma eliciting half of maximum inhibition of IR(t) or K(IN)] were 4.24 and 4.13 microg/ml, for the antipyretic and anti-inflammatory effects, respectively.

  11. A generalized item response tree model for psychological assessments.

    PubMed

    Jeon, Minjeong; De Boeck, Paul

    2016-09-01

    A new item response theory (IRT) model with a tree structure has been introduced for modeling item response processes with a tree structure. In this paper, we present a generalized item response tree model with a flexible parametric form, dimensionality, and choice of covariates. The utilities of the model are demonstrated with two applications in psychological assessments for investigating Likert scale item responses and for modeling omitted item responses. The proposed model is estimated with the freely available R package flirt (Jeon et al., 2014b).

  12. Estimating metabolic heat loss in birds and mammals by combining infrared thermography with biophysical modelling.

    PubMed

    McCafferty, D J; Gilbert, C; Paterson, W; Pomeroy, P P; Thompson, D; Currie, J I; Ancel, A

    2011-03-01

    Infrared thermography (IRT) is a technique that determines surface temperature based on physical laws of radiative transfer. Thermal imaging cameras have been used since the 1960s to determine the surface temperature patterns of a wide range of birds and mammals and how species regulate their surface temperature in response to different environmental conditions. As a large proportion of metabolic energy is transferred from the body to the environment as heat, biophysical models have been formulated to determine metabolic heat loss. These models are based on heat transfer equations for radiation, convection, conduction and evaporation and therefore surface temperature recorded by IRT can be used to calculate heat loss from different body regions. This approach has successfully demonstrated that in birds and mammals heat loss is regulated from poorly insulated regions of the body which are seen to be thermal windows for the dissipation of body heat. Rather than absolute measurement of metabolic heat loss, IRT and biophysical models have been most useful in estimating the relative heat loss from different body regions. Further calibration studies will improve the accuracy of models but the strength of this approach is that it is a non-invasive method of measuring the relative energy cost of an animal in response to different environments, behaviours and physiological states. It is likely that the increasing availability and portability of thermal imaging systems will lead to many new insights into the thermal physiology of endotherms.

  13. A mixed-binomial model for Likert-type personality measures.

    PubMed

    Allik, Jüri

    2014-01-01

    Personality measurement is based on the idea that values on an unobservable latent variable determine the distribution of answers on a manifest response scale. Typically, it is assumed in the Item Response Theory (IRT) that latent variables are related to the observed responses through continuous normal or logistic functions, determining the probability with which one of the ordered response alternatives on a Likert-scale item is chosen. Based on an analysis of 1731 self- and other-rated responses on the 240 NEO PI-3 questionnaire items, it was proposed that a viable alternative is a finite number of latent events which are related to manifest responses through a binomial function which has only one parameter-the probability with which a given statement is approved. For the majority of items, the best fit was obtained with a mixed-binomial distribution, which assumes two different subpopulations who endorse items with two different probabilities. It was shown that the fit of the binomial IRT model can be improved by assuming that about 10% of random noise is contained in the answers and by taking into account response biases toward one of the response categories. It was concluded that the binomial response model for the measurement of personality traits may be a workable alternative to the more habitual normal and logistic IRT models.

  14. A mixed-binomial model for Likert-type personality measures

    PubMed Central

    Allik, Jüri

    2014-01-01

    Personality measurement is based on the idea that values on an unobservable latent variable determine the distribution of answers on a manifest response scale. Typically, it is assumed in the Item Response Theory (IRT) that latent variables are related to the observed responses through continuous normal or logistic functions, determining the probability with which one of the ordered response alternatives on a Likert-scale item is chosen. Based on an analysis of 1731 self- and other-rated responses on the 240 NEO PI-3 questionnaire items, it was proposed that a viable alternative is a finite number of latent events which are related to manifest responses through a binomial function which has only one parameter—the probability with which a given statement is approved. For the majority of items, the best fit was obtained with a mixed-binomial distribution, which assumes two different subpopulations who endorse items with two different probabilities. It was shown that the fit of the binomial IRT model can be improved by assuming that about 10% of random noise is contained in the answers and by taking into account response biases toward one of the response categories. It was concluded that the binomial response model for the measurement of personality traits may be a workable alternative to the more habitual normal and logistic IRT models. PMID:24847291

  15. Integrating competing dimensional models of personality: linking the SNAP, TCI, and NEO using Item Response Theory.

    PubMed

    Stepp, Stephanie D; Yu, Lan; Miller, Joshua D; Hallquist, Michael N; Trull, Timothy J; Pilkonis, Paul A

    2012-04-01

    Mounting evidence suggests that several inventories assessing both normal personality and personality disorders measure common dimensional personality traits (i.e., Antagonism, Constraint, Emotional Instability, Extraversion, and Unconventionality), albeit providing unique information along the underlying trait continuum. We used Widiger and Simonsen's (2005) pantheoretical integrative model of dimensional personality assessment as a guide to create item pools. We then used Item Response Theory (IRT) to compare the assessment of these five personality traits across three established dimensional measures of personality: the Schedule for Nonadaptive and Adaptive Personality (SNAP), the Temperament and Character Inventory (TCI), and the Revised NEO Personality Inventory (NEO PI-R). We found that items from each inventory map onto these five common personality traits in predictable ways. The IRT analyses, however, documented considerable variability in the item and test information derived from each inventory. Our findings support the notion that the integration of multiple perspectives will provide greater information about personality while minimizing the weaknesses of any single instrument.

  16. Population pharmacokinetic and pharmacodynamic modeling of different formulations of ONO-5334, cathepsin K inhibitor, in Caucasian and Japanese postmenopausal females.

    PubMed

    Hasegawa, Chihiro; Ohno, Tomoya; Umemura, Takeo; Honda, Naoki; Ohyama, Michiyo; Nagase, Shinichi; Small, Maria; Deacon, Steve; Ogawa, Mikio; Ieiri, Ichiro

    2014-01-01

    ONO-5334, a selective inhibitor of cathepsin K, is a potential new treatment for osteoporosis. The objectives of this study were to (1) develop population pharmacokinetic-pharmacodynamic (PK-PD) models for ONO-5334 using dose-ascending data from healthy postmenopausal females, (2) examine comparability of PK and/or PD profile between Caucasian and Japanese, and (3) compare PK-PD profile between immediate release tablet (IRT) and sustained release tablet (SRT). The population PK-PD models were developed for each formulation for post-dose levels of bone resorption markers (serum CTX and NTX). The data were provided from 4 phase 1 studies with total of 201 Caucasian and 94 Japanese subjects. Plasma concentrations of ONO-5334 and bone resorption markers were thoroughly evaluated in those studies. An indirect response model described relationships between bone resorption markers and plasma concentrations of ONO-5334. There was no significant difference in PK and pharmacodynamic potency (IC50 ) between Caucasian and Japanese. Based on the developed model, serum CTX and NTX after administration of ONO-5334 IRT or SRT were simulated, and the results showed that ONO-5334 SRT would provide comparable PD effect on bone resorption markers with lower dose relative to IRT.

  17. Toward a hierarchical model of criminal thinking: evidence from item response theory and confirmatory factor analysis.

    PubMed

    Walters, Glenn D; Hagman, Brett T; Cohn, Amy M

    2011-12-01

    Item response theory (IRT) methods were applied to items from the 80-item Psychological Inventory of Criminal Thinking Styles (PICTS; G. D. Walters, 1995) to determine how well they measure the latent trait of criminal thinking in a group of 2,872 male medium security prison inmates. Preliminary analyses revealed that the 64 PICTS thinking style items, 32 PICTS proactive criminal thinking items, and 24 PICTS reactive criminal thinking items were sufficiently unidimensional to meet the local independence requirements of IRT. The PICTS was fitted to a 2-parameter logistic-graded response IRT model, the results of which showed that the 8 items measuring denial of harm (Sentimentality) displayed weak discrimination (a < 0.5), whereas most of the proactive and reactive items displayed moderate to good discrimination (a > 1.0). Information function analysis revealed that all 3 components of a hierarchical model of criminal thinking--PICTS total scale, PICTS proactive factor, and PICTS reactive factor--displayed greater precision at higher rather than lower levels of the trait dimension. The study findings indicate that items from the PICTS Sentimentality scale do a poor job of measuring general criminal thinking, whereas items from the other 7 PICTS thinking style scales provide their most precise estimates at the upper end of the trait dimension.

  18. Relationships among Classical Test Theory and Item Response Theory Frameworks via Factor Analytic Models

    ERIC Educational Resources Information Center

    Kohli, Nidhi; Koran, Jennifer; Henn, Lisa

    2015-01-01

    There are well-defined theoretical differences between the classical test theory (CTT) and item response theory (IRT) frameworks. It is understood that in the CTT framework, person and item statistics are test- and sample-dependent. This is not the perception with IRT. For this reason, the IRT framework is considered to be theoretically superior…

  19. Bifactor models and rotations: exploring the extent to which multidimensional data yield univocal scale scores.

    PubMed

    Reise, Steven P; Moore, Tyler M; Haviland, Mark G

    2010-11-01

    The application of psychological measures often results in item response data that arguably are consistent with both unidimensional (a single common factor) and multidimensional latent structures (typically caused by parcels of items that tap similar content domains). As such, structural ambiguity leads to seemingly endless "confirmatory" factor analytic studies in which the research question is whether scale scores can be interpreted as reflecting variation on a single trait. An alternative to the more commonly observed unidimensional, correlated traits, or second-order representations of a measure's latent structure is a bifactor model. Bifactor structures, however, are not well understood in the personality assessment community and thus rarely are applied. To address this, herein we (a) describe issues that arise in conceptualizing and modeling multidimensionality, (b) describe exploratory (including Schmid-Leiman [Schmid & Leiman, 1957] and target bifactor rotations) and confirmatory bifactor modeling, (c) differentiate between bifactor and second-order models, and (d) suggest contexts where bifactor analysis is particularly valuable (e.g., for evaluating the plausibility of subscales, determining the extent to which scores reflect a single variable even when the data are multidimensional, and evaluating the feasibility of applying a unidimensional item response theory (IRT) measurement model). We emphasize that the determination of dimensionality is a related but distinct question from either determining the extent to which scores reflect a single individual difference variable or determining the effect of multidimensionality on IRT item parameter estimates. Indeed, we suggest that in many contexts, multidimensional data can yield interpretable scale scores and be appropriately fitted to unidimensional IRT models.

  20. Environmental Durability Testing of Structural Adhesives. Part I. AF- 143-2/EC-3917; PL-729-3/PL-728

    DTIC Science & Technology

    1978-12-01

    ten analytical wipes with methanol . The last three specimens contained two faces as a result of the lap shear test. One face was yellow (adhesive...8217I;. I I. .. .... . 1.;; 11 !1;: V3M: !M M: H .. .... 11 ... M; 7. -11 Ili: N it -if N .. ....l! itK it :1,:: nrM .. .... ... .. ::ij .. -I is

  1. Psychometric Properties of IRT Proficiency Estimates

    ERIC Educational Resources Information Center

    Kolen, Michael J.; Tong, Ye

    2010-01-01

    Psychometric properties of item response theory proficiency estimates are considered in this paper. Proficiency estimators based on summed scores and pattern scores include non-Bayes maximum likelihood and test characteristic curve estimators and Bayesian estimators. The psychometric properties investigated include reliability, conditional…

  2. Progress in Characterizing Strictly Unidimensional IRT Representations

    DTIC Science & Technology

    1990-11-29

    Education Armidalie. New South Wales 23SI Research Laboratory AUTRALIA Dr. Paul Horst University 01 Illinois 677 G Sure.184 UrbanaIL 61801 Mr. Paul Foley...dimensionality of standardized tests for tile National Assessment of Educational Progress is described by Zwick (1987). 2.2 Essential independence A successful...Measurement Laboratory, Department of Educational Psy- chology, University of Illinois at Urbana-Champaign. Lord, F. M. (1980). Application of Item Response

  3. Missing Data and IRT Item Parameter Estimation.

    ERIC Educational Resources Information Center

    DeMars, Christine

    The situation of nonrandomly missing data has theoretically different implications for item parameter estimation depending on whether joint maximum likelihood or marginal maximum likelihood methods are used in the estimation. The objective of this paper is to illustrate what potentially can happen, under these estimation procedures, when there is…

  4. The Effect of Repeaters on Equating

    ERIC Educational Resources Information Center

    Kim, HeeKyoung; Kolen, Michael J.

    2010-01-01

    Test equating might be affected by including in the equating analyses examinees who have taken the test previously. This study evaluated the effect of including such repeaters on Medical College Admission Test (MCAT) equating using a population invariance approach. Three-parameter logistic (3-PL) item response theory (IRT) true score and…

  5. Real scale ray-tracing simulation of space earthshine measurement with improved BRDF model of lunar surface

    NASA Astrophysics Data System (ADS)

    Yu, Jinhee; Ryu, Dong-Ok; Ahn, Sung-Ho; Kim, Sug-Whan

    2011-09-01

    The discrepancy in annual changes of Earth albedo anomaly among the Had3CM prediction, ground and low Earth orbit measurements attracts great academic attention world-wide. As a part of our on-going study for better understanding of such discrepancy, we report a new earthshine measurement simulation technique. It combines the light source (the Sun), targets (the Earth and the Moon) and a hypothetical detector in a real scale Integrated Monte-Carlo Ray Tracing (IRT) computation environment. The Sun is expressed as a Lambertian scattering sphere, emitting 1.626x1026W over 400nm- 750nm in wavelength range. Whilst we are in the process of developing a complex Earth model consisting of land, sea and atmosphere with appropriate BRDF models, a simplified Lambertian Earth surface with 0.3 in uniform albedo was used in this study. For the moon surface, Hapke's BRDF model is used with double Henry-Green phase function. These elements were then imported into the IRT computation of radiative transfer between their surfaces. First, the irradiance levels of earthshine and moonshine lights were computed and then confirmed that they agree well with the measurement data from Big Bear Solar Observatory. They were subsequently used in determination of the Earth bond albedo of about 0.3 that is almost identical to the input Earth albedo of 0.3. These computations prove that, for the first time, the real scale IRT model was successfully deployed for the Earthshine measurement simulation and, therefore, it can be applicable for other ground and space based measurement simulation of reflected lights from the Earth and the Moon.

  6. Stochastic modeling of plasma mode forecasting in tokamak

    NASA Astrophysics Data System (ADS)

    Saadat, Sh.; Salem, M.; Ghoranneviss, M.; Khorshid, P.

    2012-04-01

    The structure of magnetohydrodynamic (MHD) modes has always been an interesting study in tokamaks. The mode number of tokamak plasma is the most important parameter, which plays a vital role in MHD instabilities. If it could be predicted, then the time of exerting external fields, such as feedback fields and Resonance Helical Field, could be obtained. Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average are useful models to predict stochastic processes. In this paper, we suggest using ARIMA model to forecast mode number. The ARIMA model shows correct mode number (m = 4) about 0.5 ms in IR-T1 tokamak and equations of Mirnov coil fluctuations are obtained. It is found that the recursive estimates of the ARIMA model parameters change as the plasma mode changes. A discriminator function has been proposed to determine plasma mode based on the recursive estimates of model parameters.

  7. Numerical Modeling of Anti-icing Systems and Comparison to Test Results on a NACA 0012 Airfoil

    NASA Technical Reports Server (NTRS)

    Al-Khalil, Kamel M.; Potapczuk, Mark G.

    1993-01-01

    A series of experimental tests were conducted in the NASA Lewis IRT on an electro-thermally heated NACA 0012 airfoil. Quantitative comparisons between the experimental results and those predicted by a computer simulation code were made to assess the validity of a recently developed anti-icing model. An infrared camera was utilized to scan the instantaneous temperature contours of the skin surface. Despite some experimental difficulties, good agreement between the numerical predictions and the experiment results were generally obtained for the surface temperature and the possibility for each runback to freeze. Some recommendations were given for an efficient operation of a thermal anti-icing system.

  8. Power and sample size determination in the Rasch model: evaluation of the robustness of a numerical method to non-normality of the latent trait.

    PubMed

    Guilleux, Alice; Blanchin, Myriam; Hardouin, Jean-Benoit; Sébille, Véronique

    2014-01-01

    Patient-reported outcomes (PRO) have gained importance in clinical and epidemiological research and aim at assessing quality of life, anxiety or fatigue for instance. Item Response Theory (IRT) models are increasingly used to validate and analyse PRO. Such models relate observed variables to a latent variable (unobservable variable) which is commonly assumed to be normally distributed. A priori sample size determination is important to obtain adequately powered studies to determine clinically important changes in PRO. In previous developments, the Raschpower method has been proposed for the determination of the power of the test of group effect for the comparison of PRO in cross-sectional studies with an IRT model, the Rasch model. The objective of this work was to evaluate the robustness of this method (which assumes a normal distribution for the latent variable) to violations of distributional assumption. The statistical power of the test of group effect was estimated by the empirical rejection rate in data sets simulated using a non-normally distributed latent variable. It was compared to the power obtained with the Raschpower method. In both cases, the data were analyzed using a latent regression Rasch model including a binary covariate for group effect. For all situations, both methods gave comparable results whatever the deviations from the model assumptions. Given the results, the Raschpower method seems to be robust to the non-normality of the latent trait for determining the power of the test of group effect.

  9. Unidimensional and Multidimensional Models for Item Response Theory.

    ERIC Educational Resources Information Center

    McDonald, Roderick P.

    This paper provides an up-to-date review of the relationship between item response theory (IRT) and (nonlinear) common factor theory and draws out of this relationship some implications for current and future research in IRT. Nonlinear common factor analysis yields a natural embodiment of the weak principle of local independence in appropriate…

  10. A Comparison of Equating Methods under the Graded Response Model.

    ERIC Educational Resources Information Center

    Cohen, Allan S.; Kim, Seock-Ho

    Equating tests from different calibrations under item response theory (IRT) requires calculation of the slope and intercept of the appropriate linear transformation. Two methods have been proposed recently for equating graded response items under IRT, a test characteristic curve method and a minimum chi-square method. These two methods are…

  11. Integrating Competing Dimensional Models of Personality: Linking the SNAP, TCI, and NEO Using Item Response Theory

    PubMed Central

    Stepp, Stephanie D.; Yu, Lan; Miller, Joshua D.; Hallquist, Michael N.; Trull, Timothy J.; Pilkonis, Paul A.

    2013-01-01

    Mounting evidence suggests that several inventories assessing both normal personality and personality disorders measure common dimensional personality traits (i.e., Antagonism, Constraint, Emotional Instability, Extraversion, and Unconventionality), albeit providing unique information along the underlying trait continuum. We used Widiger and Simonsen’s (2005) pantheoretical integrative model of dimensional personality assessment as a guide to create item pools. We then used Item Response Theory (IRT) to compare the assessment of these five personality traits across three established dimensional measures of personality: the Schedule for Nonadaptive and Adaptive Personality (SNAP), the Temperament and Character Inventory (TCI), and the Revised NEO Personality Inventory (NEO PI-R). We found that items from each inventory map onto these five common personality traits in predictable ways. The IRT analyses, however, documented considerable variability in the item and test information derived from each inventory. Our findings support the notion that the integration of multiple perspectives will provide greater information about personality while minimizing the weaknesses of any single instrument. PMID:22452759

  12. IRTPRO 2.1 for Windows (Item Response Theory for Patient-Reported Outcomes)

    ERIC Educational Resources Information Center

    Paek, Insu; Han, Kyung T.

    2013-01-01

    This article reviews a new item response theory (IRT) model estimation program, IRTPRO 2.1, for Windows that is capable of unidimensional and multidimensional IRT model estimation for existing and user-specified constrained IRT models for dichotomously and polytomously scored item response data. (Contains 1 figure and 2 notes.)

  13. A turbulence model for iced airfoils and its validation

    NASA Technical Reports Server (NTRS)

    Shin, Jaiwon; Chen, Hsun H.; Cebeci, Tuncer

    1992-01-01

    A turbulence model based on the extension of the algebraic eddy viscosity formulation of Cebeci and Smith developed for two dimensional flows over smooth and rough surfaces is described for iced airfoils and validated for computed ice shapes obtained for a range of total temperatures varying from 28 to -15 F. The validation is made with an interactive boundary layer method which uses a panel method to compute the inviscid flow and an inverse finite difference boundary layer method to compute the viscous flow. The interaction between inviscid and viscous flows is established by the use of the Hilbert integral. The calculated drag coefficients compare well with recent experimental data taken at the NASA-Lewis Icing Research Tunnel (IRT) and show that, in general, the drag increase due to ice accretion can be predicted well and efficiently.

  14. A Hierarchical Model for Accuracy and Choice on Standardized Tests.

    PubMed

    Culpepper, Steven Andrew; Balamuta, James Joseph

    2015-11-25

    This paper assesses the psychometric value of allowing test-takers choice in standardized testing. New theoretical results examine the conditions where allowing choice improves score precision. A hierarchical framework is presented for jointly modeling the accuracy of cognitive responses and item choices. The statistical methodology is disseminated in the 'cIRT' R package. An 'answer two, choose one' (A2C1) test administration design is introduced to avoid challenges associated with nonignorable missing data. Experimental results suggest that the A2C1 design and payout structure encouraged subjects to choose items consistent with their cognitive trait levels. Substantively, the experimental data suggest that item choices yielded comparable information and discrimination ability as cognitive items. Given there are no clear guidelines for writing more or less discriminating items, one practical implication is that choice can serve as a mechanism to improve score precision.

  15. Icing research tunnel test of a model helicopter rotor

    NASA Technical Reports Server (NTRS)

    Miller, Thomas L.; Bond, Thomas H.

    1989-01-01

    An experimental program has been conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in which an OH-58 tail rotor assembly was operated in a horizontal plane to simulate the action of a typical main rotor. Ice was accreted on the blades in a variety of rotor and tunnel operating conditions and documentation of the resulting shapes was performed. Rotor torque and vibration are presented as functions of time for several representative test runs, and the effects of various parametric variations on the blade ice shapes are shown. This OH-58 test was the first of its kind in the United States and will encourage additional model rotor icing tunnel testing. Although not a scaled representative of any actual full-scale main rotor system, this rig has produced torque and vibration data which will be useful in assessing the quality of existing rotor icing analyses.

  16. Item Response Theory with Estimation of the Latent Density Using Davidian Curves

    ERIC Educational Resources Information Center

    Woods, Carol M.; Lin, Nan

    2009-01-01

    Davidian-curve item response theory (DC-IRT) is introduced, evaluated with simulations, and illustrated using data from the Schedule for Nonadaptive and Adaptive Personality Entitlement scale. DC-IRT is a method for fitting unidimensional IRT models with maximum marginal likelihood estimation, in which the latent density is estimated,…

  17. The Value of Item Response Theory in Clinical Assessment: A Review

    ERIC Educational Resources Information Center

    Thomas, Michael L.

    2011-01-01

    Item response theory (IRT) and related latent variable models represent modern psychometric theory, the successor to classical test theory in psychological assessment. Although IRT has become prevalent in the measurement of ability and achievement, its contributions to clinical domains have been less extensive. Applications of IRT to clinical…

  18. Stability of Rasch Scales over Time

    ERIC Educational Resources Information Center

    Taylor, Catherine S.; Lee, Yoonsun

    2010-01-01

    Item response theory (IRT) methods are generally used to create score scales for large-scale tests. Research has shown that IRT scales are stable across groups and over time. Most studies have focused on items that are dichotomously scored. Now Rasch and other IRT models are used to create scales for tests that include polytomously scored items.…

  19. Channel modelling for free-space optical inter-HAP links using adaptive ARQ transmission

    NASA Astrophysics Data System (ADS)

    Parthasarathy, S.; Giggenbach, D.; Kirstädter, A.

    2014-10-01

    Free-space optical (FSO) communication systems have seen significant developments in recent years due to growing need for very high data rates and tap-proof communication. The operation of an FSO link is suited to diverse variety of applications such as satellites, High Altitude Platforms (HAPs), Unmanned Aerial Vehicles (UAVs), aircrafts, ground stations and other areas involving both civil and military situations. FSO communication systems face challenges due to different effects of the atmospheric channel. FSO channel primarily suffers from scintillation effects due to Index of Refraction Turbulence (IRT). In addition, acquisition and pointing becomes more difficult because of the high directivity of the transmitted beam: Miss-pointing of the transmitted beam and tracking errors at the receiver generate additional fading of the optical signal. High Altitude Platforms (HAPs) are quasi-stationary vehicles operating in the stratosphere. The slowly varying but precisely determined time-of-flight of the Inter-HAP channel adds to its characteristics. To propose a suitable ARQ scheme, proper theoretical understanding of the optical atmospheric propagation and modeling of a specific scenario FSO channel is required. In this paper, a bi-directional symmetrical Inter-HAP link has been selected and modeled. The Inter-HAP channel model is then investigated via simulations in terms of optical scintillation induced by IRT and in presence of pointing error. The performance characteristic of the model is then quantified in terms of fading statistics from which the Packet Error Probability (PEP) is calculated. Based on the PEP characteristics, we propose suitable ARQ schemes.

  20. (64)Cu-ATSM therapy targets regions with activated DNA repair and enrichment of CD133(+) cells in an HT-29 tumor model: Sensitization with a nucleic acid antimetabolite.

    PubMed

    Yoshii, Yukie; Furukawa, Takako; Matsumoto, Hiroki; Yoshimoto, Mitsuyoshi; Kiyono, Yasushi; Zhang, Ming-Rong; Fujibayashi, Yasuhisa; Saga, Tsuneo

    2016-06-28

    (64)Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) ((64)Cu-ATSM) is a potential theranostic agent targeting the over-reduced state under hypoxia within tumors. Recent clinical Cu-ATSM positron emission tomography studies have revealed a correlation between uptake and poor prognosis; however, the reason is unclear. Here, using a human colon carcinoma HT-29 model, we demonstrated that the intratumoral (64)Cu-ATSM high-uptake regions exhibited malignant characteristics, such as upregulated DNA repair and elevated %CD133(+) cancer stem-like cells. Based on this evidence, we developed a strategy to enhance the efficacy of (64)Cu-ATSM internal radiotherapy (IRT) by inhibiting DNA repair with a nucleic acid (NA) antimetabolite. The results of the analyses showed upregulation of pathways related to DNA repair along with NA incorporation (bromodeoxyuridine uptake) and elevation of %CD133(+) cells in (64)Cu-ATSM high-uptake regions. In an in vivo(64)Cu-ATSM treatment study, co-administration of an NA antimetabolite and (64)Cu-ATSM synergistically inhibited tumor growth, with little toxicity, and effectively reduced %CD133(+) cells. (64)Cu-ATSM therapy targeted malignant tumor regions with activated DNA repair and high concentrations of CD133(+) cells in the HT-29 model. NA antimetabolite co-administration can be an effective approach to enhance the therapeutic effect of (64)Cu-ATSM IRT.

  1. Measurement Bias across Gender on the Children's Depression Inventory: Evidence for Invariance from Two Latent Variable Models

    ERIC Educational Resources Information Center

    Carle, Adam C.; Millsap, Roger E.; Cole, David A.

    2008-01-01

    Confirmatory factor analysis for ordered-categorical measures (CFA-OCM) and rating scale item response theory (IRT) analyses explore measurement bias across gender on the Children's Depression Inventory (CDI) in a community sample of 779 children in the third and sixth grades. Given the set of statistical criteria, IRT and CFA-OCM generally…

  2. IRT Item Parameter Scaling for Developing New Item Pools

    ERIC Educational Resources Information Center

    Kang, Hyeon-Ah; Lu, Ying; Chang, Hua-Hua

    2017-01-01

    Increasing use of item pools in large-scale educational assessments calls for an appropriate scaling procedure to achieve a common metric among field-tested items. The present study examines scaling procedures for developing a new item pool under a spiraled block linking design. The three scaling procedures are considered: (a) concurrent…

  3. Conditional Standard Errors of Measurement for Composite Scores Using IRT

    ERIC Educational Resources Information Center

    Kolen, Michael J.; Wang, Tianyou; Lee, Won-Chan

    2012-01-01

    Composite scores are often formed from test scores on educational achievement test batteries to provide a single index of achievement over two or more content areas or two or more item types on that test. Composite scores are subject to measurement error, and as with scores on individual tests, the amount of error variability typically depends on…

  4. Examining the Reliability of Student Growth Percentiles Using Multidimensional IRT

    ERIC Educational Resources Information Center

    Monroe, Scott; Cai, Li

    2015-01-01

    Student growth percentiles (SGPs, Betebenner, 2009) are used to locate a student's current score in a conditional distribution based on the student's past scores. Currently, following Betebenner (2009), quantile regression (QR) is most often used operationally to estimate the SGPs. Alternatively, multidimensional item response theory (MIRT) may…

  5. A Comparative Study of IRT Fixed Parameter Calibration Methods

    ERIC Educational Resources Information Center

    Kim, Seonghoon

    2006-01-01

    This article provides technical descriptions of five fixed parameter calibration (FPC) methods, which were based on marginal maximum likelihood estimation via the EM algorithm, and evaluates them through simulation. The five FPC methods described are distinguished from each other by how many times they update the prior ability distribution and by…

  6. Section Preequating under the Equivalent Groups Design without IRT

    ERIC Educational Resources Information Center

    Guo, Hongwen; Puhan, Gautam

    2014-01-01

    In this article, we introduce a section preequating (SPE) method (linear and nonlinear) under the randomly equivalent groups design. In this equating design, sections of Test X (a future new form) and another existing Test Y (an old form already on scale) are administered. The sections of Test X are equated to Test Y, after adjusting for the…

  7. Evaluation of Linking Methods for Multidimensional IRT Calibrations

    ERIC Educational Resources Information Center

    Min, Kyung-Seok

    2007-01-01

    Most researchers agree that psychological/educational tests are sensitive to multiple traits, implying the need for a multidimensional item response theory (MIRT). One limitation of applying a MIRT in practice is the difficulty in establishing equivalent scales of multiple traits. In this study, a new MIRT linking method was proposed and evaluated…

  8. The Effect of Changing Content on IRT Scaling Methods

    ERIC Educational Resources Information Center

    Keller, Lisa A.; Keller, Robert R.

    2015-01-01

    Equating test forms is an essential activity in standardized testing, with increased importance with the accountability systems in existence through the mandate of Adequate Yearly Progress. It is through equating that scores from different test forms become comparable, which allows for the tracking of changes in the performance of students from…

  9. Construct continuity in the presence of multidimensionality

    NASA Astrophysics Data System (ADS)

    Staniewska, Dorota

    Unidimensionality -- a condition, under which only one dominant construct is being measured by the test, is a fundamental assumption of most modern day psychometric models. However, some tests are multidimensional by design. A test, for instance, might measure physics, biology and chemistry subscales combined to measure a "general science" composite. The relative magnitudes of those subscales sometimes shift from administration to administration, which results in an altered composite. This study examined the conditions under which two different forms of a multidimensional test measure the same composite construct to a degree that allows them to be equated, i.e. used interchangeably. IRT true-score equating was used in a simulation study to assess the closeness of the scores on the forms. Conditions examined included the correlations between subscales, varying number of items per subscale form to form, and different subpopulation ability estimates on the subscales. Differences in the equating errors due to generating model (1PL or 3PL) were also examined. A way of calculating a unidimensional composite from a two-dimensional ability was devised and compared to the unidimensional composite obtained from Parscale. It was found that in general, the errors increase with decreasing correlation between traits and increased divergence of the two forms to be equated, with the later being the main predictor of the equating errors. However, the magnitude of those errors was small for the population as a whole especially when all examinee abilities are drawn from the same distribution. It was concluded that IRT true score equating is relatively robust to multidimensionality for the conditions examined, especially if the overall population score is desired. However, when accurate estimate of the equated score for individuals at the extremes of the population is needed, or whenever population abilities are drawn from more than one distribution, the unidimensional true score

  10. Modeling the World Health Organization Disability Assessment Schedule II using non-parametric item response models.

    PubMed

    Galindo-Garre, Francisca; Hidalgo, María Dolores; Guilera, Georgina; Pino, Oscar; Rojo, J Emilio; Gómez-Benito, Juana

    2015-03-01

    The World Health Organization Disability Assessment Schedule II (WHO-DAS II) is a multidimensional instrument developed for measuring disability. It comprises six domains (getting around, self-care, getting along with others, life activities and participation in society). The main purpose of this paper is the evaluation of the psychometric properties for each domain of the WHO-DAS II with parametric and non-parametric Item Response Theory (IRT) models. A secondary objective is to assess whether the WHO-DAS II items within each domain form a hierarchy of invariantly ordered severity indicators of disability. A sample of 352 patients with a schizophrenia spectrum disorder is used in this study. The 36 items WHO-DAS II was administered during the consultation. Partial Credit and Mokken scale models are used to study the psychometric properties of the questionnaire. The psychometric properties of the WHO-DAS II scale are satisfactory for all the domains. However, we identify a few items that do not discriminate satisfactorily between different levels of disability and cannot be invariantly ordered in the scale. In conclusion the WHO-DAS II can be used to assess overall disability in patients with schizophrenia, but some domains are too general to assess functionality in these patients because they contain items that are not applicable to this pathology.

  11. Evaluation of Icing Scaling on Swept NACA 0012 Airfoil Models

    NASA Technical Reports Server (NTRS)

    Tsao, Jen-Ching; Lee, Sam

    2012-01-01

    Icing scaling tests in the NASA Glenn Icing Research Tunnel (IRT) were performed on swept wing models using existing recommended scaling methods that were originally developed for straight wing. Some needed modifications on the stagnation-point local collection efficiency (i.e., beta(sub 0) calculation and the corresponding convective heat transfer coefficient for swept NACA 0012 airfoil models have been studied and reported in 2009, and the correlations will be used in the current study. The reference tests used a 91.4-cm chord, 152.4-cm span, adjustable sweep airfoil model of NACA 0012 profile at velocities of 100 and 150 knot and MVD of 44 and 93 mm. Scale-to-reference model size ratio was 1:2.4. All tests were conducted at 0deg angle of attack (AoA) and 45deg sweep angle. Ice shape comparison results were presented for stagnation-point freezing fractions in the range of 0.4 to 1.0. Preliminary results showed that good scaling was achieved for the conditions test by using the modified scaling methods developed for swept wing icing.

  12. Results of a sub-scale model rotor icing test

    NASA Technical Reports Server (NTRS)

    Flemming, Robert J.; Bond, Thomas H.; Britton, Randall K.

    1991-01-01

    A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters, is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested.

  13. Limited information estimation of the diffusion-based item response theory model for responses and response times.

    PubMed

    Ranger, Jochen; Kuhn, Jörg-Tobias; Szardenings, Carsten

    2016-05-01

    Psychological tests are usually analysed with item response models. Recently, some alternative measurement models have been proposed that were derived from cognitive process models developed in experimental psychology. These models consider the responses but also the response times of the test takers. Two such models are the Q-diffusion model and the D-diffusion model. Both models can be calibrated with the diffIRT package of the R statistical environment via marginal maximum likelihood (MML) estimation. In this manuscript, an alternative approach to model calibration is proposed. The approach is based on weighted least squares estimation and parallels the standard estimation approach in structural equation modelling. Estimates are determined by minimizing the discrepancy between the observed and the implied covariance matrix. The estimator is simple to implement, consistent, and asymptotically normally distributed. Least squares estimation also provides a test of model fit by comparing the observed and implied covariance matrix. The estimator and the test of model fit are evaluated in a simulation study. Although parameter recovery is good, the estimator is less efficient than the MML estimator.

  14. Revisiting the 4-Parameter Item Response Model: Bayesian Estimation and Application.

    PubMed

    Culpepper, Steven Andrew

    2016-12-01

    There has been renewed interest in Barton and Lord's (An upper asymptote for the three-parameter logistic item response model (Tech. Rep. No. 80-20). Educational Testing Service, 1981) four-parameter item response model. This paper presents a Bayesian formulation that extends Béguin and Glas (MCMC estimation and some model fit analysis of multidimensional IRT models. Psychometrika, 66 (4):541-561, 2001) and proposes a model for the four-parameter normal ogive (4PNO) model. Monte Carlo evidence is presented concerning the accuracy of parameter recovery. The simulation results support the use of less informative uniform priors for the lower and upper asymptotes, which is an advantage to prior research. Monte Carlo results provide some support for using the deviance information criterion and [Formula: see text] index to choose among models with two, three, and four parameters. The 4PNO is applied to 7491 adolescents' responses to a bullying scale collected under the 2005-2006 Health Behavior in School-Aged Children study. The results support the value of the 4PNO to estimate lower and upper asymptotes in large-scale surveys.

  15. Ice-Accretion Test Results for Three Large-Scale Swept-Wing Models in the NASA Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Potapczuk, Mark G.; Lee, Sam; Malone, Adam M.; Paul, Bernard P., Jr.; Woodard, Brian S.

    2016-01-01

    Icing simulation tools and computational fluid dynamics codes are reaching levels of maturity such that they are being proposed by manufacturers for use in certification of aircraft for flight in icing conditions with increasingly less reliance on natural-icing flight testing and icing-wind-tunnel testing. Sufficient high-quality data to evaluate the performance of these tools is not currently available. The objective of this work was to generate a database of ice-accretion geometry that can be used for development and validation of icing simulation tools as well as for aerodynamic testing. Three large-scale swept wing models were built and tested at the NASA Glenn Icing Research Tunnel (IRT). The models represented the Inboard (20 percent semispan), Midspan (64 percent semispan) and Outboard stations (83 percent semispan) of a wing based upon a 65 percent scale version of the Common Research Model (CRM). The IRT models utilized a hybrid design that maintained the full-scale leading-edge geometry with a truncated afterbody and flap. The models were instrumented with surface pressure taps in order to acquire sufficient aerodynamic data to verify the hybrid model design capability to simulate the full-scale wing section. A series of ice-accretion tests were conducted over a range of total temperatures from -23.8 to -1.4 C with all other conditions held constant. The results showed the changing ice-accretion morphology from rime ice at the colder temperatures to highly 3-D scallop ice in the range of -11.2 to -6.3 C. Warmer temperatures generated highly 3-D ice accretion with glaze ice characteristics. The results indicated that the general scallop ice morphology was similar for all three models. Icing results were documented for limited parametric variations in angle of attack, drop size and cloud liquid-water content (LWC). The effect of velocity on ice accretion was documented for the Midspan and Outboard models for a limited number of test cases. The data suggest

  16. Ice-Accretion Test Results for Three Large-Scale Swept-Wing Models in the NASA Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Potapczuk, Mark G.; Lee, Sam; Malone, Adam M.; Paul, Benard P., Jr.; Woodard, Brian S.

    2016-01-01

    Icing simulation tools and computational fluid dynamics codes are reaching levels of maturity such that they are being proposed by manufacturers for use in certification of aircraft for flight in icing conditions with increasingly less reliance on natural-icing flight testing and icing-wind-tunnel testing. Sufficient high-quality data to evaluate the performance of these tools is not currently available. The objective of this work was to generate a database of ice-accretion geometry that can be used for development and validation of icing simulation tools as well as for aerodynamic testing. Three large-scale swept wing models were built and tested at the NASA Glenn Icing Research Tunnel (IRT). The models represented the Inboard (20% semispan), Midspan (64% semispan) and Outboard stations (83% semispan) of a wing based upon a 65% scale version of the Common Research Model (CRM). The IRT models utilized a hybrid design that maintained the full-scale leading-edge geometry with a truncated afterbody and flap. The models were instrumented with surface pressure taps in order to acquire sufficient aerodynamic data to verify the hybrid model design capability to simulate the full-scale wing section. A series of ice-accretion tests were conducted over a range of total temperatures from -23.8 deg C to -1.4 deg C with all other conditions held constant. The results showed the changing ice-accretion morphology from rime ice at the colder temperatures to highly 3-D scallop ice in the range of -11.2 deg C to -6.3 deg C. Warmer temperatures generated highly 3-D ice accretion with glaze ice characteristics. The results indicated that the general scallop ice morphology was similar for all three models. Icing results were documented for limited parametric variations in angle of attack, drop size and cloud liquid-water content (LWC). The effect of velocity on ice accretion was documented for the Midspan and Outboard models for a limited number of test cases. The data suggest that

  17. Further Refinement of the LEWICE SLD Model

    NASA Technical Reports Server (NTRS)

    Wright, William B.

    2006-01-01

    A research project is underway at NASA Glenn Research Center to produce computer software that can accurately predict ice growth for any meteorological conditions for any aircraft surface. This report will present results from version 3.2 of this software, which is called LEWICE. This version differs from previous releases in that it incorporates additional thermal analysis capabilities, a pneumatic boot model, interfaces to external computational fluid dynamics (CFD) flow solvers and has an empirical model for the supercooled large droplet (SLD) regime. An extensive comparison against the database of ice shapes and collection efficiencies that have been generated in the NASA Glenn Icing Research Tunnel (IRT) has also been performed. The complete set of data used for this comparison will eventually be available in a contractor report. This paper will show the differences in collection efficiency and ice shape between LEWICE 3.2 and experimental data. This report will first describe the LEWICE 3.2 SLD model. A semi-empirical approach was used to incorporate first order physical effects of large droplet phenomena into icing software. Comparisons are then made to every two-dimensional case in the water collection database and the ice shape database. Each collection efficiency condition was run using the following four assumptions: 1) potential flow, no splashing; 2) potential flow, with splashing; 3) Navior-Stokes, no splashing; 4) Navi r-Stokes, with splashing. All cases were run with 21 bin drop size distributions and a lift correction (angle of attack adjustment). Quantitative comparisons are shown for impingement limit, maximum water catch, and total collection efficiency. Due to the large number of ice shape cases, comprehensive comparisons were limited to potential flow cases with and without splashing. Quantitative comparisons are shown for horn height, horn angle, icing limit, area, and leading edge thickness. The results show that the predicted results for

  18. OptiPhy, a technical-economic optimisation model for improving the management of plant protection practices in agriculture: a decision-support tool for controlling the toxicity risks related to pesticides.

    PubMed

    Mghirbi, Oussama; LE Grusse, Philippe; Fabre, Jacques; Mandart, Elisabeth; Bord, Jean-Paul

    2017-03-01

    The health, environmental and socio-economic issues related to the massive use of plant protection products are a concern for all the stakeholders involved in the agricultural sector. These stakeholders, including farmers and territorial actors, have expressed a need for decision-support tools for the management of diffuse pollution related to plant protection practices and their impacts. To meet the needs expressed by the public authorities and the territorial actors for such decision-support tools, we have developed a technical-economic model "OptiPhy" for risk mitigation based on indicators of pesticide toxicity risk to applicator health (IRSA) and to the environment (IRTE), under the constraint of suitable economic outcomes. This technical-economic optimisation model is based on linear programming techniques and offers various scenarios to help the different actors in choosing plant protection products, depending on their different levels of constraints and aspirations. The health and environmental risk indicators can be broken down into sub-indicators so that management can be tailored to the context. This model for technical-economic optimisation and management of plant protection practices can analyse scenarios for the reduction of pesticide-related risks by proposing combinations of substitution PPPs, according to criteria of efficiency, economic performance and vulnerability of the natural environment. The results of the scenarios obtained on real ITKs in different cropping systems show that it is possible to reduce the PPP pressure (TFI) and reduce toxicity risks to applicator health (IRSA) and to the environment (IRTE) by up to approximately 50 %.

  19. A Comprehensive Approach for Assessing Person Fit with Test-Retest Data

    ERIC Educational Resources Information Center

    Ferrando, Pere J.

    2014-01-01

    Item response theory (IRT) models allow model-data fit to be assessed at the individual level by using person-fit indices. This assessment is also feasible when IRT is used to model test-retest data. However, person-fit developments for this type of modeling are virtually nonexistent. This article proposes a general person-fit approach for…

  20. A test of the International Personality Item Pool representation of the Revised NEO Personality Inventory and development of a 120-item IPIP-based measure of the five-factor model.

    PubMed

    Maples, Jessica L; Guan, Li; Carter, Nathan T; Miller, Joshua D

    2014-12-01

    There has been a substantial increase in the use of personality assessment measures constructed using items from the International Personality Item Pool (IPIP) such as the 300-item IPIP-NEO (Goldberg, 1999), a representation of the Revised NEO Personality Inventory (NEO PI-R; Costa & McCrae, 1992). The IPIP-NEO is free to use and can be modified to accommodate its users' needs. Despite the substantial interest in this measure, there is still a dearth of data demonstrating its convergence with the NEO PI-R. The present study represents an investigation of the reliability and validity of scores on the IPIP-NEO. Additionally, we used item response theory (IRT) methodology to create a 120-item version of the IPIP-NEO. Using an undergraduate sample (n = 359), we examined the reliability, as well as the convergent and criterion validity, of scores from the 300-item IPIP-NEO, a previously constructed 120-item version of the IPIP-NEO (Johnson, 2011), and the newly created IRT-based IPIP-120 in comparison to the NEO PI-R across a range of outcomes. Scores from all 3 IPIP measures demonstrated strong reliability and convergence with the NEO PI-R and a high degree of similarity with regard to their correlational profiles across the criterion variables (rICC = .983, .972, and .976, respectively). The replicability of these findings was then tested in a community sample (n = 757), and the results closely mirrored the findings from Sample 1. These results provide support for the use of the IPIP-NEO and both 120-item IPIP-NEO measures as assessment tools for measurement of the five-factor model.

  1. Investigation of approximations in thermal-hydraulic modeling of core conversions

    SciTech Connect

    Garner, Patrick L.; Hanan, Nelson A.

    2008-07-15

    Neutronics analyses for core conversions are usually fairly detailed, for example representing all 4 flats and all 4 corners of all 6 tubes of all 20 IRT-3M or -4M fuel assemblies in the core of the VVR-SM reactor in Uzbekistan. The coupled neutronics and thermal-hydraulic analysis for safety analysis transients is usually less detailed, for example modeling only a hot and an average fuel plate and the associated coolant. Several of the approximations have been studied using the RELAP5 and PARET computer codes in order to provide assurance that the lack of full detail is not important to the safety analysis. Two specific cases studied are (1) representation of a core of same- type fuel assemblies by a hot and an average assembly each having multiple channels as well as by merely a hot and average channel and (2) modeling a core containing multiple fuel types as the sum of fractional core models for each fuel type. (author)

  2. A New Extension of the Binomial Error Model for Responses to Items of Varying Difficulty in Educational Testing and Attitude Surveys.

    PubMed

    Wiley, James A; Martin, John Levi; Herschkorn, Stephen J; Bond, Jason

    2015-01-01

    We put forward a new item response model which is an extension of the binomial error model first introduced by Keats and Lord. Like the binomial error model, the basic latent variable can be interpreted as a probability of responding in a certain way to an arbitrarily specified item. For a set of dichotomous items, this model gives predictions that are similar to other single parameter IRT models (such as the Rasch model) but has certain advantages in more complex cases. The first is that in specifying a flexible two-parameter Beta distribution for the latent variable, it is easy to formulate models for randomized experiments in which there is no reason to believe that either the latent variable or its distribution vary over randomly composed experimental groups. Second, the elementary response function is such that extensions to more complex cases (e.g., polychotomous responses, unfolding scales) are straightforward. Third, the probability metric of the latent trait allows tractable extensions to cover a wide variety of stochastic response processes.

  3. A New Extension of the Binomial Error Model for Responses to Items of Varying Difficulty in Educational Testing and Attitude Surveys

    PubMed Central

    Wiley, James A.; Martin, John Levi; Herschkorn, Stephen J.; Bond, Jason

    2015-01-01

    We put forward a new item response model which is an extension of the binomial error model first introduced by Keats and Lord. Like the binomial error model, the basic latent variable can be interpreted as a probability of responding in a certain way to an arbitrarily specified item. For a set of dichotomous items, this model gives predictions that are similar to other single parameter IRT models (such as the Rasch model) but has certain advantages in more complex cases. The first is that in specifying a flexible two-parameter Beta distribution for the latent variable, it is easy to formulate models for randomized experiments in which there is no reason to believe that either the latent variable or its distribution vary over randomly composed experimental groups. Second, the elementary response function is such that extensions to more complex cases (e.g., polychotomous responses, unfolding scales) are straightforward. Third, the probability metric of the latent trait allows tractable extensions to cover a wide variety of stochastic response processes. PMID:26544974

  4. Measuring Mathematical Knowledge for Teaching Fractions with Drawn Quantities

    ERIC Educational Resources Information Center

    Izsak, Andrew; Jacobson, Erik; de Araujo, Zandra; Orrill, Chandra Hawley

    2012-01-01

    Researchers have recently used traditional item response theory (IRT) models to measure mathematical knowledge for teaching (MKT). Some studies (e.g., Hill, 2007; Izsak, Orrill, Cohen, & Brown, 2010), however, have reported subgroups when measuring middle-grades teachers' MKT, and such groups violate a key assumption of IRT models. This study…

  5. A Note on Stochastic Ordering of the Latent Trait Using the Sum of Polytomous Item Scores

    ERIC Educational Resources Information Center

    van der Ark, L. Andries; Bergsma, Wicher P.

    2010-01-01

    In contrast to dichotomous item response theory (IRT) models, most well-known polytomous IRT models do not imply stochastic ordering of the latent trait by the total test score (SOL). This has been thought to make the ordering of respondents on the latent trait using the total test score questionable and throws doubt on the justifiability of using…

  6. Bayesian Modal Estimation of the Four-Parameter Item Response Model in Real, Realistic, and Idealized Data Sets.

    PubMed

    Waller, Niels G; Feuerstahler, Leah

    2017-03-17

    In this study, we explored item and person parameter recovery of the four-parameter model (4PM) in over 24,000 real, realistic, and idealized data sets. In the first analyses, we fit the 4PM and three alternative models to data from three Minnesota Multiphasic Personality Inventory-Adolescent form factor scales using Bayesian modal estimation (BME). Our results indicated that the 4PM fits these scales better than simpler item Response Theory (IRT) models. Next, using the parameter estimates from these real data analyses, we estimated 4PM item parameters in 6,000 realistic data sets to establish minimum sample size requirements for accurate item and person parameter recovery. Using a factorial design that crossed discrete levels of item parameters, sample size, and test length, we also fit the 4PM to an additional 18,000 idealized data sets to extend our parameter recovery findings. Our combined results demonstrated that 4PM item parameters and parameter functions (e.g., item response functions) can be accurately estimated using BME in moderate to large samples (N ⩾ 5, 000) and person parameters can be accurately estimated in smaller samples (N ⩾ 1, 000). In the supplemental files, we report annotated [Formula: see text] code that shows how to estimate 4PM item and person parameters in [Formula: see text] (Chalmers, 2012 ).

  7. A Nominal Response Model Approach for Detecting Answer Copying.

    ERIC Educational Resources Information Center

    Wollack, James A.

    1997-01-01

    Introduces a new Item Response Theory (IRT) based statistic for detecting answer copying. Compares this omega statistic with the best classical test theory-based statistic under various conditions, and finds omega superior based on Type I error rate and power. (SLD)

  8. The Sequential Probability Ratio Test and Binary Item Response Models

    ERIC Educational Resources Information Center

    Nydick, Steven W.

    2014-01-01

    The sequential probability ratio test (SPRT) is a common method for terminating item response theory (IRT)-based adaptive classification tests. To decide whether a classification test should stop, the SPRT compares a simple log-likelihood ratio, based on the classification bound separating two categories, to prespecified critical values. As has…

  9. Heat Transfer Measurements on Surfaces with Natural Ice Castings and Modeled Roughness

    NASA Technical Reports Server (NTRS)

    Breuer, Kenneth S.; Torres, Benjamin E.; Orr, D. J.; Hansman, R. John

    1997-01-01

    An experimental method is described to measure and compare the convective heat transfer coefficient of natural and simulated ice accretion roughness and to provide a rational means for determining accretion-related enhanced heat transfer coefficients. The natural ice accretion roughness was a sample casting made from accretions at the NASA Lewis Icing Research Tunnel (IRT). One of these castings was modeled using a Spectral Estimation Technique (SET) to produce three roughness elements patterns that simulate the actual accretion. All four samples were tested in a flat-plate boundary layer at angle of attack in a "dry" wind tunnel test. The convective heat transfer coefficient was measured using infrared thermography. It is shown that, dispite some problems in the current data set, the method does show considerable promise in determining roughness-induced heat transfer coefficients, and that, in addition to the roughness height and spacing in the flow direction, the concentration and spacing of elements in the spanwise direction are important parameters.

  10. A review of ice accretion data from a model rotor icing test and comparison with theory

    NASA Technical Reports Server (NTRS)

    Britton, Randall K.; Bond, Thomas H.

    1991-01-01

    An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are shown as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.

  11. A review of ice accretion data from a model rotor icing test and comparison with theory

    NASA Technical Reports Server (NTRS)

    Britton, Randall K.; Bond, Thomas H.

    1991-01-01

    An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are drawn as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.

  12. A Comment on Early Student Blunders on Computer-Based Adaptive Tests

    ERIC Educational Resources Information Center

    Green, Bert F.

    2011-01-01

    This article refutes a recent claim that computer-based tests produce biased scores for very proficient test takers who make mistakes on one or two initial items and that the "bias" can be reduced by using a four-parameter IRT model. Because the same effect occurs with pattern scores on nonadaptive tests, the effect results from IRT scoring, not…

  13. Person Response Functions and the Definition of Units in the Social Sciences

    ERIC Educational Resources Information Center

    Engelhard, George, Jr.; Perkins, Aminah F.

    2011-01-01

    Humphry (this issue) has written a thought-provoking piece on the interpretation of item discrimination parameters as scale units in item response theory. One of the key features of his work is the description of an item response theory (IRT) model that he calls the logistic measurement function that combines aspects of two traditions in IRT that…

  14. Improving the Quality and Applicability of the Dutch Scales of the Communication Profile for the Hearing Impaired Using Item Response Theory

    ERIC Educational Resources Information Center

    Mokkink, Lidwine B.; Knol, Dirk L.; van Nispen, Ruth M. A.; Kramer, Sophia E.

    2010-01-01

    Purpose: The aim of this study was to improve the quality and applicability of the 6 Dutch scales of the Communication Profile for the Hearing Impaired (CPHI; Demorest & Erdman, 1986, 1987, 1988) using item response theory (IRT). IRT modeling can produce precise, valid, and relatively brief instruments, resulting in minimal response burden (Edelen…

  15. An Item Response Theory Analysis of Harter's Self-Perception Profile for Children or Why Strong Clinical Scales Should Be Distrusted

    ERIC Educational Resources Information Center

    Egberink, Iris J. L.; Meijer, Rob R.

    2011-01-01

    The authors investigated the psychometric properties of the subscales of the Self-Perception Profile for Children with item response theory (IRT) models using a sample of 611 children. Results from a nonparametric Mokken analysis and a parametric IRT approach for boys (n = 268) and girls (n = 343) were compared. The authors found that most scales…

  16. The Use of Unidimensional Item Parameter Estimates of Multidimensional Items in Adaptive Testing.

    ERIC Educational Resources Information Center

    Ackerman, Terry A.

    The purpose of this study was to investigate the effect of using multidimensional items in a computer adaptive test (CAT) setting which assumes a unidimensional item response theory (IRT) framework. Previous research has suggested that the composite of multidimensional abilities being estimated by a unidimensional IRT model is not constant…

  17. Practical Guide to Conducting an Item Response Theory Analysis

    ERIC Educational Resources Information Center

    Toland, Michael D.

    2014-01-01

    Item response theory (IRT) is a psychometric technique used in the development, evaluation, improvement, and scoring of multi-item scales. This pedagogical article provides the necessary information needed to understand how to conduct, interpret, and report results from two commonly used ordered polytomous IRT models (Samejima's graded…

  18. An Overview of Nonlinear Factor Analysis and Its Relationship to Item Response Theory.

    ERIC Educational Resources Information Center

    De Champlain, Andre

    An approach that is currently gaining popularity in educational measurement is one that treats item response theory (IRT) as a special case of nonlinear factor analysis (NLFA). A brief overview is provided of some of the research that has examined the relationship between IRT and NLFA. Three NLFA models are outlined, emphasizing their major…

  19. Detecting Local Item Dependence in Polytomous Adaptive Data

    ERIC Educational Resources Information Center

    Mislevy, Jessica L.; Rupp, Andre A.; Harring, Jeffrey R.

    2012-01-01

    A rapidly expanding arena for item response theory (IRT) is in attitudinal and health-outcomes survey applications, often with polytomous items. In particular, there is interest in computer adaptive testing (CAT). Meeting model assumptions is necessary to realize the benefits of IRT in this setting, however. Although initial investigations of…

  20. Automated Model Atmosphere Generator Program (AMAG)

    DTIC Science & Technology

    1980-02-01

    PINIMUM OF ZHGT VS W11 -C’ S CAIC .’ WIT wiMU OF- IRT VS STt) "f~O R POPALkj5E HGT C C IPUT ir rUTPUT RECUIRFEMETS C INPUT TIRrUcH ARGLMENT LIST C ’CUPLI...increases linearly at a fixed rate of 4m /sec per kilometer. Wind speed can thus be calculated for any geometric height as a function of the ground wind speed

  1. Effects of Unequal Ability Variances on the Performance of Logistic Regression, Mantel-Haenszel, SIBTEST IRT, and IRT Likelihood Ratio for DIF Detection

    ERIC Educational Resources Information Center

    Pei, Lai Kwan; Li, Jun

    2010-01-01

    Differential item functioning (DIF) of items has become an important issue in test fairness and equity in large-scale assessments. DIF occurs when subgroups of test takers have equal trait levels but differ in their probabilities of a correct response. DIF items may threaten the validity of test scores for subgroups and can mislead researchers…

  2. Transient analysis for the tajoura critical facility with IRT-2M HEU fuel and IRT-4M leu fuel : ANL independent verification results.

    SciTech Connect

    Garner, P. L.; Hanan, N. A.

    2005-12-02

    Calculations have been performed for postulated transients in the Critical Facility at the Tajoura Nuclear Research Center (TNRC) in Libya. These calculations have been performed at the request of staff of the Renewable Energy and Water Desalinization Research Center (REWDRC) who are performing similar calculations. The transients considered were established during a working meeting between ANL and REWDRC staff on October 1-2, 2005 and subsequent email correspondence. Calculations were performed for the current high-enriched uranium (HEU) core and the proposed low-enriched uranium (LEU) core. These calculations have been performed independently from those being performed by REWDRC and serve as one step in the verification process.

  3. Transient analyses for the Uzbekistan VVR-SM reactor with IRT-3M HEU fuel and IRT-4M LEU fuel : ANL independent verification results.

    SciTech Connect

    Garner, P. L.; Hanan, N. A.; Nuclear Engineering Division

    2007-09-24

    Calculations have been performed for postulated transients in the VVR-SM Reactor at the Institute of Nuclear Physics (INP) of the Academy of Sciences in the Republic of Uzbekistan. (The reactor designation in Cyrillic is BBP-CM; transliterating characters to English gives VVRSM but translating words gives WWR-SM.) These calculations have been performed at the request of staff of the INP who are performing similar calculations. The transients considered were established during working meetings between Argonne National Laboratory (ANL) and INP staff during summer 2006 [Ref. 1], subsequent email correspondence, and subsequent staff visits. Calculations were performed for the current high-enriched uranium (HEU) core, the proposed low-enriched uranium (LEU) core, and one mixed HEU-LEU core during the transition. These calculations have been performed independently from those being performed by INP and serve as one step in the verification process.

  4. The multi-dimensional model of Māori identity and cultural engagement: item response theory analysis of scale properties.

    PubMed

    Sibley, Chris G; Houkamau, Carla A

    2013-01-01

    We argue that there is a need for culture-specific measures of identity that delineate the factors that most make sense for specific cultural groups. One such measure, recently developed specifically for Māori peoples, is the Multi-Dimensional Model of Māori Identity and Cultural Engagement (MMM-ICE). Māori are the indigenous peoples of New Zealand. The MMM-ICE is a 6-factor measure that assesses the following aspects of identity and cultural engagement as Māori: (a) group membership evaluation, (b) socio-political consciousness, (c) cultural efficacy and active identity engagement, (d) spirituality, (e) interdependent self-concept, and (f) authenticity beliefs. This article examines the scale properties of the MMM-ICE using item response theory (IRT) analysis in a sample of 492 Māori. The MMM-ICE subscales showed reasonably even levels of measurement precision across the latent trait range. Analysis of age (cohort) effects further indicated that most aspects of Māori identification tended to be higher among older Māori, and these cohort effects were similar for both men and women. This study provides novel support for the reliability and measurement precision of the MMM-ICE. The study also provides a first step in exploring change and stability in Māori identity across the life span. A copy of the scale, along with recommendations for scale scoring, is included.

  5. Item Response Theory and Health Outcomes Measurement in the 21st Century

    PubMed Central

    Hays, Ron D.; Morales, Leo S.; Reise, Steve P.

    2006-01-01

    Item response theory (IRT) has a number of potential advantages over classical test theory in assessing self-reported health outcomes. IRT models yield invariant item and latent trait estimates (within a linear transformation), standard errors conditional on trait level, and trait estimates anchored to item content. IRT also facilitates evaluation of differential item functioning, inclusion of items with different response formats in the same scale, and assessment of person fit and is ideally suited for implementing computer adaptive testing. Finally, IRT methods can be helpful in developing better health outcome measures and in assessing change over time. These issues are reviewed, along with a discussion of some of the methodological and practical challenges in applying IRT methods. PMID:10982088

  6. Lord-Wingersky Algorithm Version 2.0 for Hierarchical Item Factor Models with Applications in Test Scoring, Scale Alignment, and Model Fit Testing. CRESST Report 830

    ERIC Educational Resources Information Center

    Cai, Li

    2013-01-01

    Lord and Wingersky's (1984) recursive algorithm for creating summed score based likelihoods and posteriors has a proven track record in unidimensional item response theory (IRT) applications. Extending the recursive algorithm to handle multidimensionality is relatively simple, especially with fixed quadrature because the recursions can be defined…

  7. The Assessment of Risk in Educational Incentive Contracts.

    ERIC Educational Resources Information Center

    Morey, Richard C.

    1980-01-01

    Presents a stochastic model and subsequent risk analysis that should enable an administrator to evaluate an incentive contract. A numerical illustration points out the types of issues that can be addressed by the model. (Author/IRT)

  8. Structure of the Complexity Parameter of the Test Physic Problem in Rasch Model

    ERIC Educational Resources Information Center

    Volov, Vyacheslav T.; Gilev, Alexander A.

    2016-01-01

    In today's item response theory (IRT) the response to the test item is considered as a probability event depending on the student's ability and difficulty of items. It is noted that in the scientific literature there is very little agreement about how to determine factors affecting the item difficulty. It is suggested that the difficulty of the…

  9. A Note on the Reliability Coefficients for Item Response Model-Based Ability Estimates

    ERIC Educational Resources Information Center

    Kim, Seonghoon

    2012-01-01

    Assuming item parameters on a test are known constants, the reliability coefficient for item response theory (IRT) ability estimates is defined for a population of examinees in two different ways: as (a) the product-moment correlation between ability estimates on two parallel forms of a test and (b) the squared correlation between the true…

  10. Stability Analysis of the Viscous Polytropic Dark Energy Model in Einstein Cosmology

    NASA Astrophysics Data System (ADS)

    Wang, Yue-Yi; Chen, Ju-Hua; Wang, Yong-Jiu

    2016-10-01

    Not Available Supported by the National Natural Science Foundation of China under Grant No 10873004, the State Key Development Program for Basic Research Program of China under Grant No 2010CB832803, and the Program for Changjiang Scholars and Innovative Research Team in University under Grant No IRT0964.

  11. Toward a Hierarchical Model of Criminal Thinking: Evidence from Item Response Theory and Confirmatory Factor Analysis

    ERIC Educational Resources Information Center

    Walters, Glenn D.; Hagman, Brett T.; Cohn, Amy M.

    2011-01-01

    Item response theory (IRT) methods were applied to items from the 80-item Psychological Inventory of Criminal Thinking Styles (PICTS; G. D. Walters, 1995) to determine how well they measure the latent trait of criminal thinking in a group of 2,872 male medium security prison inmates. Preliminary analyses revealed that the 64 PICTS thinking style…

  12. The Role of Psychometric Modeling in Test Validation: An Application of Multidimensional Item Response Theory

    ERIC Educational Resources Information Center

    Schilling, Stephen G.

    2007-01-01

    In this paper the author examines the role of item response theory (IRT), particularly multidimensional item response theory (MIRT) in test validation from a validity argument perspective. The author provides justification for several structural assumptions and interpretations, taking care to describe the role he believes they should play in any…

  13. Mean structure analysis from an IRT approach: an application in the context of organizational psychology.

    PubMed

    Revuelta Menéndez, Javier; Ximénez Gómez, Carmen

    2012-11-01

    The application of mean and covariance structure analysis with quantitative data is increasing. However, latent means analysis with qualitative data is not as widespread. This article summarizes the procedures to conduct an analysis of latent means of dichotomous data from an item response theory approach. We illustrate the implementation of these procedures in an empirical example referring to the organizational context, where a multi-group analysis was conducted to compare the latent means of three employee groups in two factors measuring personal preferences and the perceived degree of rewards from the organization. Results show that higher personal motivations are associated with higher perceived importance of the organization, and that these perceptions differ across groups, so that higher-level employees have a lower level of personal and perceived motivation. The article shows how to estimate the factor means and the factor correlation from dichotomous data, and how to assess goodness of fit. Lastly, we provide the M-Plus syntax code in order to facilitate the latent means analyses for applied researchers.

  14. IRT Analysis of General Outcome Measures in Grades 1-8. Technical Report # 0916

    ERIC Educational Resources Information Center

    Alonzo, Julie; Anderson, Daniel; Tindal, Gerald

    2009-01-01

    We present scaling outcomes for mathematics assessments used in the fall to screen students at risk of failing to learn the knowledge and skills described in the National Council of Teachers of Mathematics (NCTM) Focal Point Standards. At each grade level, the assessment consisted of a 48-item test with three 16-item sub-test sets aligned to the…

  15. Creating IRT-Based Parallel Test Forms Using the Genetic Algorithm Method

    ERIC Educational Resources Information Center

    Sun, Koun-Tem; Chen, Yu-Jen; Tsai, Shu-Yen; Cheng, Chien-Fen

    2008-01-01

    In educational measurement, the construction of parallel test forms is often a combinatorial optimization problem that involves the time-consuming selection of items to construct tests having approximately the same test information functions (TIFs) and constraints. This article proposes a novel method, genetic algorithm (GA), to construct parallel…

  16. Unidimensional IRT Item Parameter Estimates across Equivalent Test Forms with Confounding Specifications within Dimensions

    ERIC Educational Resources Information Center

    Matlock, Ki Lynn; Turner, Ronna

    2016-01-01

    When constructing multiple test forms, the number of items and the total test difficulty are often equivalent. Not all test developers match the number of items and/or average item difficulty within subcontent areas. In this simulation study, six test forms were constructed having an equal number of items and average item difficulty overall.…

  17. Using IRT DIF Methods to Evaluate the Validity of Score Gains. CSE Technical Report 660

    ERIC Educational Resources Information Center

    Koretz, Daniel M.; McCaffrey, Daniel F.

    2005-01-01

    Given current high-stakes uses of tests, one of the most pressing and difficult problems confronting the field of measurement is to develop better methods for distinguishing between meaningful gains in performance and score inflation. This study explores the potential usefulness of adapting differential item functioning (DIF) techniques for this…

  18. The Impact of Multidirectional Item Parameter Drift on IRT Scaling Coefficients and Proficiency Estimates

    ERIC Educational Resources Information Center

    Han, Kyung T.; Wells, Craig S.; Sireci, Stephen G.

    2012-01-01

    Item parameter drift (IPD) occurs when item parameter values change from their original value over time. IPD may pose a serious threat to the fairness and validity of test score interpretations, especially when the goal of the assessment is to measure growth or improvement. In this study, we examined the effect of multidirectional IPD (i.e., some…

  19. Effects on Scale Linking of Different Definitions of Criterion Functions for the IRT Characteristic Curve Methods

    ERIC Educational Resources Information Center

    Kim, Seonghoon; Kolen, Michael J.

    2007-01-01

    Under item response theory, the characteristic curve methods (Haebara and Stocking-Lord methods) are used to link two ability scales from separate calibrations. The linking methods use their respective criterion functions that can be defined differently according to the symmetry- and distribution-related schemes. The symmetry-related scheme…

  20. An Investigation of Methods for Reducing Sampling Error in Certain IRT (Item Response Theory) Procedures.

    DTIC Science & Technology

    1983-08-01

    spaced sample of 1500 6a drawn from the ability estimates obtained by LOGIST for a regular administration of the Test of English as a Foreign Language... TOEFL ). A spaced sample of fifteen items were drawn from the sixty TOEFL items whose parameters were estimated in the same run as the abilities. The

  1. Screening of Phonological Awareness in the Early Elementary Grades: An IRT Approach

    ERIC Educational Resources Information Center

    Vloedgraven, Judith M. T.; Verhoeven, Ludo

    2007-01-01

    The purpose of the present study was to explore the possibilities for the assessment of growth in phonological awareness of children in kindergarten and first grade. Phonological awareness was measured using four sets of items involving rhyming, phoneme identification, phoneme blending, and phoneme segmentation. The results of an exploratory…

  2. A HO-IRT Based Diagnostic Assessment System with Constructed Response Items

    ERIC Educational Resources Information Center

    Yang, Chih-Wei; Kuo, Bor-Chen; Liao, Chen-Huei

    2011-01-01

    The aim of the present study was to develop an on-line assessment system with constructed response items in the context of elementary mathematics curriculum. The system recorded the problem solving process of constructed response items and transfered the process to response codes for further analyses. An inference mechanism based on artificial…

  3. A Bootstrap Generalization of Modified Parallel Analysis for IRT Dimensionality Assessment

    ERIC Educational Resources Information Center

    Finch, Holmes; Monahan, Patrick

    2008-01-01

    This article introduces a bootstrap generalization to the Modified Parallel Analysis (MPA) method of test dimensionality assessment using factor analysis. This methodology, based on the use of Marginal Maximum Likelihood nonlinear factor analysis, provides for the calculation of a test statistic based on a parametric bootstrap using the MPA…

  4. Sensitivity of IRT Equating to the Behavior of Test Equating Items.

    ERIC Educational Resources Information Center

    Michaelides, Michalis P.

    The delta-plot method is used to identify which common items in a common item nonequivalent groups design for test equating show large changes in their p-values across administrations. Outliers in that plot denote differential item behavior and are candidates for exclusion from the common item pool. This study investigated whether keeping or…

  5. An IRT Analysis of Preservice Teacher Self-Efficacy in Technology Integration

    ERIC Educational Resources Information Center

    Browne, Jeremy

    2011-01-01

    The need for rigorously developed measures of preservice teacher traits regarding technology integration training has been acknowledged (Kay 2006), but such instruments are still extremely rare. The Technology Integration Confidence Scale (TICS) represents one such measure, but past analyses of its functioning have been limited by sample size and…

  6. THE INDIUM-GALLIUM RADIATION LOOP OF THE IRT NUCLEAR REACTOR,

    DTIC Science & Technology

    NUCLEAR REACTORS, *ISOTOPES), (*INDIUM, *GALLIUM), GAMMA RAYS, NEUTRONS, INTERMETALLIC COMPOUNDS, ALUMINUM, SHIELDING, GENERATORS, EUTECTICS, ARGON, OXALIC ACID , ELECTROMAGNETIC PUMPS, HALF LIFE, HEAT TRANSFER

  7. The Long-Term Sustainability of IRT Scaling Methods in Mixed-Format Tests

    ERIC Educational Resources Information Center

    Keller, Lisa A.; Hambleton, Ronald K.

    2013-01-01

    Due to recent research in equating methodologies indicating that some methods may be more susceptible to the accumulation of equating error over multiple administrations, the sustainability of several item response theory methods of equating over time was investigated. In particular, the paper is focused on two equating methodologies: fixed common…

  8. Process Developed for Forming Urethane Ice Models

    NASA Technical Reports Server (NTRS)

    Vannuyen, Thomas

    1998-01-01

    A new process for forming ice shapes on an aircraft wing was developed at the NASA Lewis Research Center. The innovative concept was formed by Lewis' Icing Research Tunnel (IRT) team, and the hardware was manufactured by Lewis' Manufacturing Engineering Division. This work was completed to increase our understanding of the stability and control of aircraft during icing conditions. This project will also enhance our evaluation of true aerodynamic wind tunnel effects on aircraft. In addition, it can be used as a design tool for evaluating ice protection systems.

  9. Super-Micro Computer Weather Prediction Model

    DTIC Science & Technology

    1992-01-01

    1s n1l ni< s-x . t te Ow. i I.4idil St i-ie./ irti,iti(00 airl!’ wellI. (o-;(il s ire, ilsu :irt.’st.’iLcd Solre I;ro! 1 11;11- S i~l-lI;I t l 0ll...rao, = 0 (B.4) at cp-f. - aw = Q (B.5) dt- where p = T& + a( aw /at + V • V7) dt and V = ia/ax + ja/ay In order to preserve conservative properties in

  10. Schools for Developing Countries: The Turkish Village Institutes

    ERIC Educational Resources Information Center

    Yilmaz, Omer

    1977-01-01

    Describes experimental village institutes whose goal was to develop and maintain the village, to help transform it into a modern village so that Turkey's pattern of development would not follow the European model of urbanization. (Author/IRT)

  11. Validation of the Crime and Violence Scale (CVS) against the Rasch Measurement Model Including Differences by Gender, Race, and Age

    ERIC Educational Resources Information Center

    Conrad, Kendon J.; Riley, Barth B.; Conrad, Karen M.; Chan, Ya-Fen; Dennis, Michael L.

    2010-01-01

    In assessing criminality, researchers have used counts of crimes, arrests, and so on, because interval measures were not available. Additionally, crime seriousness varies depending on demographic factors. This study examined the Crime and Violence Scale (CVS) regarding psychometric quality using item response theory (IRT) and invariance of the…

  12. Robustness of Lord's Formulas for Item Difficulty and Discrimination Conversions between Classical and Item Response Theory Models

    ERIC Educational Resources Information Center

    Dawber, Teresa; Rogers, W. Todd; Carbonaro, Michael

    2009-01-01

    Lord (1980) proposed formulas that provide direct relationships between IRT discrimination and difficulty parameters and conventional item statistics. The purpose of the present study was to determine the robustness of the formulas beyond the initial and restrictive conditions identified by Lord. Simulation and real achievement data were employed.…

  13. Linking Parameter Estimates Derived from an Item Response Model through Separate Calibrations. Research Report. ETS RR-09-40

    ERIC Educational Resources Information Center

    Haberman, Shelby J.

    2009-01-01

    A regression procedure is developed to link simultaneously a very large number of item response theory (IRT) parameter estimates obtained from a large number of test forms, where each form has been separately calibrated and where forms can be linked on a pairwise basis by means of common items. An application is made to forms in which a…

  14. Substantiation of parameters of the geometric model of the research reactor core for the calculation using the Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Radaev, A. I.; Schurovskaya, M. V.

    2015-12-01

    The choice of the spatial nodalization for the calculation of the power density and burnup distribution in a research reactor core with fuel assemblies of the IRT-3M and VVR-KN type using the program based on the Monte Carlo code is described. The influence of the spatial nodalization on the results of calculating basic neutronic characteristics and calculation time is investigated.

  15. Substantiation of parameters of the geometric model of the research reactor core for the calculation using the Monte Carlo method

    SciTech Connect

    Radaev, A. I. Schurovskaya, M. V.

    2015-12-15

    The choice of the spatial nodalization for the calculation of the power density and burnup distribution in a research reactor core with fuel assemblies of the IRT-3M and VVR-KN type using the program based on the Monte Carlo code is described. The influence of the spatial nodalization on the results of calculating basic neutronic characteristics and calculation time is investigated.

  16. Going Places No Infrared Temperature Devices Have Gone Before

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Exergen's IRt/c is a self-powered sensor that matches a thermocouple within specified temperature ranges and provides a predictable and repeatable signal outside of this specified range. Possessing an extremely fast time constant, the infrared technology allows users to measure product temperature without touching the product. The IRt/c uses a device called a thermopile to measure temperature and generate current. Traditionally, these devices are not available in a size that would be compatible with the Exergen IRt/c, based on NASA s quarterinch specifications. After going through five circuit designs to find a thermopile that would suit the IRt/c design and match the signal needed for output, Exergen maintains that it developed a model that totaled just 20 percent of the volume of the previous smallest detector in the world. Following completion of the project with Glenn, Exergen continued development of the IRt/c for other customers, spinning off a new product line called the micro IRt/c. This latest development has broadened applications for industries that previously could not use infrared thermometers due to size constraints. The first commercial use of the micro IRt/c involved an original equipment manufacturer that makes laminating machinery consisting of heated rollers in very tight spots. Accurate temperature measurement for this application requires close proximity to the heated rollers. With the micro IRt/c s 50-millisecond time constant, the manufacturer is able to gain closer access to the intended temperature targets for exact readings, thereby increasing productivity and staying ahead of competition.In a separate application, the infrared temperature sensor is being utilized for avalanche warnings in Switzerland. The IRt/c is mounted about 5 meters above the ground to measure the snow cover throughout the mountainous regions of the country.

  17. Comparative Meta-Analysis of Prazosin and Imagery Rehearsal Therapy for Nightmare Frequency, Sleep Quality, and Posttraumatic Stress

    PubMed Central

    Seda, Gilbert; Sanchez-Ortuno, Maria M.; Welsh, Carolyn H.; Halbower, Ann C.; Edinger, Jack D.

    2015-01-01

    Study Objective: In this meta-analysis, we compare the short-term efficacy of prazosin vs. IRT on nightmares, sleep quality, and posttraumatic stress symptoms (PTSS). Methods: Reference databases were searched for randomized controlled trials using IRT or prazosin for nightmares, sleep disturbance, and/or PTSS. Effect sizes were calculated by subtracting the mean posttest score in the control group from the mean posttest score in the treatment group, and dividing the result by the pooled standard deviation of both groups. Mixed effects models were performed to evaluate effects of treatment characteristics, as well as sample characteristics (veteran vs. civilian) on treatment efficacy. Results: Four studies used prazosin, 10 used IRT alone or in combination with another psychological treatment, and 1 included a group receiving prazosin and another group receiving IRT. Overall effect sizes of both treatments were of moderate magnitude for nightmare frequency, sleep quality, and PTSS (p < 0.01). Effect size was not significantly different with type of treatment (psychological vs. pharmacological) on nightmare frequency (p = 0.79), sleep quality (p = 0.65), or PTSS, (p = 0.52). IRT combined with CBT for insomnia showed more improvement in sleep quality compared to prazosin (p = 0.03), IRT alone (p = 0.03), or IRT combined with another psychological intervention, (p < 0.01). Conclusion: Although IRT interventions and prazosin yield comparable acute effects for the treatment of nightmares, adding CBT for insomnia to IRT seems to enhance treatment outcomes pertaining to sleep quality and PTSS. More randomized clinical trials with long-term follow-up are warranted. Commentary: A commentary on this article appears in this issue on page 9. Citation: Seda G, Sanchez-Ortuno MM, Welsh CH, Halbower AC, Edinger JD. Comparative meta-analysis of prazosin and imagery rehearsal therapy for nightmare frequency, sleep quality, and posttraumatic stress. J Clin Sleep Med 2015;11(1):11

  18. Item response theory and the measurement of psychiatric constructs: some empirical and conceptual issues and challenges.

    PubMed

    Reise, S P; Rodriguez, A

    2016-07-01

    Item response theory (IRT) measurement models are now commonly used in educational, psychological, and health-outcomes measurement, but their impact in the evaluation of measures of psychiatric constructs remains limited. Herein we present two, somewhat contradictory, theses. The first is that, when skillfully applied, IRT has much to offer psychiatric measurement in terms of scale development, psychometric analysis, and scoring. The second argument, however, is that psychiatric measurement presents some unique challenges to the application of IRT - challenges that may not be easily addressed by application of conventional IRT models and methods. These challenges include, but are not limited to, the modeling of conceptually narrow constructs and their associated limited item pools, and unipolar constructs where the expected latent trait distribution is highly skewed.

  19. Item response theory and the measurement of clinical change.

    PubMed

    Reise, Steven P; Haviland, Mark G

    2005-06-01

    An instrument's sensitivity to detect individual-level change is an important consideration for both psychometric and clinical researchers. In this article, we develop a cognitive problems measure and evaluate its sensitivity to detect change from an item response theory (IRT) perspective. After illustrating assumption checking and model fit assessment, we detail 4 features of IRT modeling: (a) the scale information curve and its relation to the bandwidth of measurement precision, (b) the scale response curve and how it is used to link the latent trait metric with the raw score metric, (c) content-based versus norm-based score referencing, and (d) the level of measurement of the latent trait scale. We conclude that IRT offers an informative, alternative framework for understanding an instrument's psychometric properties and recommend that IRT analyses be considered prior to investigations of change, growth, or the effectiveness of clinical interventions.

  20. Models and role models.

    PubMed

    ten Cate, Jacob M

    2015-01-01

    Developing experimental models to understand dental caries has been the theme in our research group. Our first, the pH-cycling model, was developed to investigate the chemical reactions in enamel or dentine, which lead to dental caries. It aimed to leverage our understanding of the fluoride mode of action and was also utilized for the formulation of oral care products. In addition, we made use of intra-oral (in situ) models to study other features of the oral environment that drive the de/remineralization balance in individual patients. This model addressed basic questions, such as how enamel and dentine are affected by challenges in the oral cavity, as well as practical issues related to fluoride toothpaste efficacy. The observation that perhaps fluoride is not sufficiently potent to reduce dental caries in the present-day society triggered us to expand our knowledge in the bacterial aetiology of dental caries. For this we developed the Amsterdam Active Attachment biofilm model. Different from studies on planktonic ('single') bacteria, this biofilm model captures bacteria in a habitat similar to dental plaque. With data from the combination of these models, it should be possible to study separate processes which together may lead to dental caries. Also products and novel agents could be evaluated that interfere with either of the processes. Having these separate models in place, a suggestion is made to design computer models to encompass the available information. Models but also role models are of the utmost importance in bringing and guiding research and researchers.

  1. Molecular Imaging and Therapy of Prostate Cancer

    DTIC Science & Technology

    2015-10-01

    Our objective is to develop an arsenic-based radiopharmaceutical platform for IGF1R-targeted imaging and therapy of PCa. The hypothesis is that...arsenic-based, IGF1R-targeted radiopharmaceuticals can allow for PET imaging, IRT, and monitoring the therapeutic response of PCa. Specific Aims: Aim 1: To...models with PET imaging. Aim 3: To monitor the efficacy of 76As-based IRT of PCa with multimodality imaging.

  2. Models, Fiction, and Fictional Models

    NASA Astrophysics Data System (ADS)

    Liu, Chuang

    2014-03-01

    The following sections are included: * Introduction * Why Most Models in Science Are Not Fictional * Typically Fictional Models in Science * Modeling the Unobservable * Fictional Models for the Unobservable? * References

  3. Item-response-theory analysis of two scales for self-efficacy for exercise behavior in people with arthritis.

    PubMed

    Mielenz, Thelma J; Edwards, Michael C; Callahan, Leigh F

    2011-07-01

    Benefits of physical activity for those with arthritis are clear, yet physical activity is difficult to initiate and maintain. Self-efficacy is a key modifiable psychosocial determinant of physical activity. This study examined two scales for self-efficacy for exercise behavior (SEEB) to identify their strengths and weaknesses using item response theory (IRT) from community-based randomized controlled trials of physical activity programs in adults with arthritis. The 2 SEEB scales included the 9-item scale by Resnick developed with older adults and the 5-item scale by Marcus developed with employed adults. All IRT analyses were conducted using the graded-response model. IRT assumptions were assessed using both exploratory and confirmatory factor analysis. The IRT analyses indicated that these scales are precise and reliable measures for identifying people with arthritis and low SEEB. The Resnick SEEB scale is slightly more precise at lower levels of self-efficacy in older adults with arthritis.

  4. In-flight investigations of the unsteady behaviour of the boundary layer with infrared thermography

    NASA Astrophysics Data System (ADS)

    Szewczyk, Mariusz; Smusz, Robert; de Groot, Klaus; Meyer, Joerg; Kucaba-Pietal, Anna; Rzucidlo, Pawel

    2017-04-01

    Infrared thermography (IRT) has been well established in wind tunnel and flight tests for the last decade. Former applications of IRT were focused, in nearly all cases, on steady measurements. In the last years, requirements of unsteady IRT measurements (up to 10 Hz) have been formulated, but the problem of a very slow thermal response of common materials of wind tunnel models or airplane components has to be overcome by finding a surface modification with a fast thermal response (low heat capacity, low thermal conductivity and high thermal diffusivity). Therefore, lab investigations of potential material combinations and flight tests with a ‘low cost’ aircraft, i.e. a glider with a modified wing surface, were conducted. In order to induce unsteady conditions (rapid change of laminar-turbulent boundary layer transition), special maneuvers of a glider during IRT measurements were performed.

  5. How States Can Reduce the Dropout Rate for Undocumented Immigrant Youth: The Effects of In-State Resident Tuition Policies

    PubMed Central

    Potochnick, Stephanie

    2016-01-01

    As of December 2011, 13 states have adopted an in-state resident tuition (IRT) policy that provides in-state tuition to undocumented immigrants and several other states are considering similar legislation. While previous research focuses on how IRT policies affect college entry and attainment, this study examines the effect these policies have on high school dropout behavior. Using the Current Population Survey (CPS) and difference-in-difference models, this paper examines whether IRT policies reduce the likelihood of dropping out of high school for Mexican foreign-born non-citizens (FBNC), a proxy for undocumented youth. The policy is estimated to cause an eight percentage point reduction in the proportion that drops out of high school. The paper develops an integrated framework that combines human capital theory with segmented assimilation theory to provide insight into how IRT policies influence student motivation and educational attainment at the high school level. PMID:24576624

  6. How states can reduce the dropout rate for undocumented immigrant youth: the effects of in-state resident tuition policies.

    PubMed

    Potochnick, Stephanie

    2014-05-01

    As of December 2011, 13 states have adopted an in-state resident tuition (IRT) policy that provides in-state tuition to undocumented immigrants and several other states are considering similar legislation. While previous research focuses on how IRT policies affect college entry and attainment, this study examines the effect these policies have on high school dropout behavior. Using the Current Population Survey (CPS) and difference-in-difference models, this paper examines whether IRT policies reduce the likelihood of dropping out of high school for Mexican foreign-born non-citizens (FBNC), a proxy for undocumented youth. The policy is estimated to cause an eight percentage point reduction in the proportion that drops out of high school. The paper develops an integrated framework that combines human capital theory with segmented assimilation theory to provide insight into how IRT policies influence student motivation and educational attainment at the high school level.

  7. Building an Evaluation Scale using Item Response Theory

    PubMed Central

    Lalor, John P.; Wu, Hao; Yu, Hong

    2016-01-01

    Evaluation of NLP methods requires testing against a previously vetted gold-standard test set and reporting standard metrics (accuracy/precision/recall/F1). The current assumption is that all items in a given test set are equal with regards to difficulty and discriminating power. We propose Item Response Theory (IRT) from psychometrics as an alternative means for gold-standard test-set generation and NLP system evaluation. IRT is able to describe characteristics of individual items - their difficulty and discriminating power - and can account for these characteristics in its estimation of human intelligence or ability for an NLP task. In this paper, we demonstrate IRT by generating a gold-standard test set for Recognizing Textual Entailment. By collecting a large number of human responses and fitting our IRT model, we show that our IRT model compares NLP systems with the performance in a human population and is able to provide more insight into system performance than standard evaluation metrics. We show that a high accuracy score does not always imply a high IRT score, which depends on the item characteristics and the response pattern.1 PMID:28004039

  8. Mental Models, Conceptual Models, and Modelling.

    ERIC Educational Resources Information Center

    Greca, Ileana Maria; Moreira, Marco Antonio

    2000-01-01

    Reviews science education research into representations constructed by students in their interactions with the world, its phenomena, and artefacts. Features discussions of mental models, conceptual models, and the activity of modeling. (Contains 30 references.) (Author/WRM)

  9. Prophylactic effect of probiotics on the development of experimental autoimmune myasthenia gravis.

    PubMed

    Chae, Chang-Suk; Kwon, Ho-Keun; Hwang, Ji-Sun; Kim, Jung-Eun; Im, Sin-Hyeog

    2012-01-01

    Probiotics are live bacteria that confer health benefits to the host physiology. Although protective role of probiotics have been reported in diverse diseases, no information is available whether probiotics can modulate neuromuscular immune disorders. We have recently demonstrated that IRT5 probiotics, a mixture of 5 probiotics, could suppress diverse experimental disorders in mice model. In this study we further investigated whether IRT5 probiotics could modulate the progression of experimental autoimmune myasthenia gravis (EAMG). Myasthenia gravis (MG) is a T cell dependent antibody mediated autoimmune disorder in which acetylcholine receptor (AChR) at the neuromuscular junction is the major auto-antigen. Oral administration of IRT5 probiotics significantly reduced clinical symptoms of EAMG such as weight loss, body trembling and grip strength. Prophylactic effect of IRT5 probiotics on EMAG is mediated by down-regulation of effector function of AChR-reactive T cells and B cells. Administration of IRT5 probiotics decreased AChR-reactive lymphocyte proliferation, anti-AChR reactive IgG levels and inflammatory cytokine levels such as IFN-γ, TNF-α, IL-6 and IL-17. Down-regulation of inflammatory mediators in AChR-reactive lymphocytes by IRT5 probiotics is mediated by the generation of regulatory dendritic cells (rDCs) that express increased levels of IL-10, TGF-β, arginase 1 and aldh1a2. Furthermore, DCs isolated from IRT5 probiotics-fed group effectively converted CD4(+) T cells into CD4(+)Foxp3(+) regulatory T cells compared with control DCs. Our data suggest that IRT5 probiotics could be applicable to modulate antibody mediated autoimmune diseases including myasthenia gravis.

  10. Approaching to the ideal condition of plasma confinement by applying external resonant fields in IR-T1 tokamak

    NASA Astrophysics Data System (ADS)

    Meshkani, Sakineh; Ghoranneviss, Mahmood; Lafouti, Mansoureh

    2015-06-01

    For understanding the effect of resonant helical magnetic field (RHF) and bias on the edge plasma turbulent transport, the radial and poloidal electric field (Er, EP ), poloidal and toroidal magnetic field (BP, Br ) were detected by the Langmuir probe, magnetic probe and diamagnetic loop. The poloidal, toroidal and radial velocity (VP, Vr, Vt ) can be determined from the electric and magnetic field. In the present work, we have investigated the effect of the magnitude of bias (V bias = 200v, V bias = 320v) on Er, EP, BP, Bt, VP, Vr, Vt . Moreover, we applied RHF with L = 2, L = 3 and L = 2 and 3 and investigate the effect of the helical windings radius on above parameters. Also, the experiment was repeated by applying the positive biasing potentials and RHF's simultaneously. The results show that by applying bias to the plasma at t = 15 msec at r/a = 0.9, Er , BP and Bt increase while EP decreases. The best modification occurs at V bias = 200v. By applying RHF to the plasma, both the electric and magnetic field vary. Er reaches the highest in the presence of RHF with L = 3. The same results are obtained for BP, Bt, VP and Vt . While the inverse results are obtained for EP and Vr . Finally, RHF and bias are applied simultaneously to the plasma. With applied bias with V bias = 200v and RHF with L = 2 and 3, we reach to the ideal circumstance. The same results obtain in the situation with V bias = 320v and RHF with L = 2 and 3.

  11. Effects of Estimation Bias on Multiple-Category Classification with an IRT-Based Adaptive Classification Procedure

    ERIC Educational Resources Information Center

    Yang, Xiangdong; Poggio, John C.; Glasnapp, Douglas R.

    2006-01-01

    The effects of five ability estimators, that is, maximum likelihood estimator, weighted likelihood estimator, maximum a posteriori, expected a posteriori, and Owen's sequential estimator, on the performances of the item response theory-based adaptive classification procedure on multiple categories were studied via simulations. The following…

  12. Evaluating IRT- and CTT-Based Methods of Estimating Classification Consistency and Accuracy Indices from Single Administrations

    ERIC Educational Resources Information Center

    Deng, Nina

    2011-01-01

    Three decision consistency and accuracy (DC/DA) methods, the Livingston and Lewis (LL) method, LEE method, and the Hambleton and Han (HH) method, were evaluated. The purposes of the study were: (1) to evaluate the accuracy and robustness of these methods, especially when their assumptions were not well satisfied, (2) to investigate the "true"…

  13. The Langer-Improved Wald Test for DIF Testing with Multiple Groups: Evaluation and Comparison to Two-Group IRT

    ERIC Educational Resources Information Center

    Woods, Carol M.; Cai, Li; Wang, Mian

    2013-01-01

    Differential item functioning (DIF) occurs when the probability of responding in a particular category to an item differs for members of different groups who are matched on the construct being measured. The identification of DIF is important for valid measurement. This research evaluates an improved version of Lord's chi [superscript 2]…

  14. Implementation of the MPC and A Operations Monitoring (MOM) System at IRT-T FSRE Nuclear Power Institute (NPI)

    SciTech Connect

    Sitdikov,I.; Zenkov, A.; Tsibulnikov, Y.; Duncan, C.; Brownell, L.; Pratt, W.T.; Carbonaro, J.; White, R.M.; Coffing, J.A.

    2008-07-13

    The Material Protection, Control and Accounting (MPC&A) Program has been working since 1994 with nuclear sites in Russia to upgrade the physical protection (PP) and material control and accounting (MC&A) functions at facilities containing weapons usable nuclear material. In early 2001, the MPC&A program initiated the MPC&A Operations Monitoring (MOM) Project to monitor facilities where MPC&A upgrades have been installed to provide increased confidence that personnel are present and vigilant, provide confidence that security procedures are being properly performed and provide additional assurance that nuclear materials have not been stolen. The MOM project began as a pilot project at the Moscow State Engineering Physics Institute (MEPhI) and a MOM system was successfully installed in October 2001. Following the success of the MEPhI pilot project, the MPC&A Program expanded the installation of MOM systems to several other Russian facilities, including the Nuclear Physics Institute (NPI) in Tomsk. The MOM system was made operational at NPI in October 2004. This paper is focused on the experience gained from operation of this system and the objectives of the MOM system. The paper also describes how the MOM system is used at NPI and, in particular, how the data is analyzed. Finally, potential expansion of the MOM system at NPI is described.

  15. IRT-Related Factor Analytic Procedures for Testing the Equivalence of Paper-and-Pencil and Internet-Administered Questionnaires

    ERIC Educational Resources Information Center

    Ferrando, Pere J.; Lorenzo-Seva, Urbano

    2005-01-01

    This article describes a general item response theory-based factor analytic procedure that allows assessment of the equivalence between 2 administrative modes of a questionnaire: paper and pencil, and Internet based. The theoretical relations between the present procedure and other methods used in previous empirical research are shown, and the…

  16. Effects of Local Item Dependence on the Validity of IRT Item, Test, and Ability Statistics. MCAT Monograph.

    ERIC Educational Resources Information Center

    Zenisky, April L.; Hambleton, Ronald K.; Sireci, Stephen G.

    Measurement specialists routinely assume examinee responses to test items are independent of one another. However, previous research has shown that many contemporary tests contain item dependencies and not accounting for these dependencies leads to misleading estimates of item, test, and ability parameters. In this study, methods for detecting…

  17. The Language Factor in Elementary Mathematics Assessments: Computational Skills and Applied Problem Solving in a Multidimensional IRT Framework

    ERIC Educational Resources Information Center

    Hickendorff, Marian

    2013-01-01

    The results of an exploratory study into measurement of elementary mathematics ability are presented. The focus is on the abilities involved in solving standard computation problems on the one hand and problems presented in a realistic context on the other. The objectives were to assess to what extent these abilities are shared or distinct, and…

  18. Independent Verification of Research Reactor Operation (Analysis of the Georgian IRT-M Reactor by the Isotope Ratio Method)

    SciTech Connect

    Cliff, John B.; Frank, Douglas P.; Gerlach, David C.; Gesh, Christopher J.; Little, Winston W.; Reid, Bruce D.; Tsiklauri, Georgi V.; Abramidze, Sh; Rostomashvili, Z.; Kiknadze, G.; Dzhavakhishvily, O.; Nabakhtiani, G.

    2010-08-11

    The U.S. Department of Energy’s Office of Nonproliferation and International Security (NA-24) develops technologies to aid in implementing international nuclear safeguards. The Isotope Ratio Method (IRM) was successfully developed in 2005 – 2007 by Pacific Northwest National Laboratory (PNNL) and the Republic of Georgia’s Andronikashvili Institute of Physics as a generic technology to verify the declared operation of water-moderated research reactors, independent of spent fuel inventory. IRM estimates the energy produced over the operating lifetime of a fission reactor by measuring the ratios of the isotopes of trace impurity elements in non-fuel reactor components.The Isotope Ratio Method is a technique for estimating the energy produced over the operating lifetime of a fission reactor by measuring the ratios of the isotopes of impurity elements in non-fuel reactor components.

  19. Towards power and sample size calculations for the comparison of two groups of patients with item response theory models.

    PubMed

    Hardouin, Jean-Benoit; Amri, Sarah; Feddag, Mohand-Larbi; Sébille, Véronique

    2012-05-20

    Evaluation of patient-reported outcomes (PRO) is increasingly performed in health sciences. PRO differs from other measurements because such patient characteristics cannot be directly observed. Item response theory (IRT) is an attractive way for PRO analysis. However, in the framework of IRT, sample size justification is rarely provided or ignores the fact that PRO measures are latent variables with the use of formulas developed for observed variables. It might therefore be inappropriate and might provide inadequately sized studies. The objective was to develop valid sample size methodology for the comparison of PRO in two groups of patients using IRT. The proposed approach takes into account questionnaire's items parameters, the difference of the latent variables means, and its variance whose derivation is approximated using Cramer-Rao bound (CRB). We also computed the associated power. We realized a simulation study taking into account sample size, number of items, and value of the group effect. We compared power obtained from CRB with the one obtained from simulations (SIM) and with the power based on observed variables (OBS). For a given sample size, powers using CRB and SIM were similar and always lower than OBS. We observed a strong impact of the number of items for CRB and SIM, the power increasing with the questionnaire's length but not for OBS. In the context of latent variables, it seems important to use an adapted sample size formula because the formula developed for observed variables seems to be inadequate and leads to an underestimated study size.

  20. The Organization of Controller Motifs Leading to Robust Plant Iron Homeostasis.

    PubMed

    Agafonov, Oleg; Selstø, Christina Helen; Thorsen, Kristian; Xu, Xiang Ming; Drengstig, Tormod; Ruoff, Peter

    2016-01-01

    Iron is an essential element needed by all organisms for growth and development. Because iron becomes toxic at higher concentrations iron is under homeostatic control. Plants face also the problem that iron in the soil is tightly bound to oxygen and difficult to access. Plants have therefore developed special mechanisms for iron uptake and regulation. During the last years key components of plant iron regulation have been identified. How these components integrate and maintain robust iron homeostasis is presently not well understood. Here we use a computational approach to identify mechanisms for robust iron homeostasis in non-graminaceous plants. In comparison with experimental results certain control arrangements can be eliminated, among them that iron homeostasis is solely based on an iron-dependent degradation of the transporter IRT1. Recent IRT1 overexpression experiments suggested that IRT1-degradation is iron-independent. This suggestion appears to be misleading. We show that iron signaling pathways under IRT1 overexpression conditions become saturated, leading to a breakdown in iron regulation and to the observed iron-independent degradation of IRT1. A model, which complies with experimental data places the regulation of cytosolic iron at the transcript level of the transcription factor FIT. Including the experimental observation that FIT induces inhibition of IRT1 turnover we found a significant improvement in the system's response time, suggesting a functional role for the FIT-mediated inhibition of IRT1 degradation. By combining iron uptake with storage and remobilization mechanisms a model is obtained which in a concerted manner integrates iron uptake, storage and remobilization. In agreement with experiments the model does not store iron during its high-affinity uptake. As an iron biofortification approach we discuss the possibility how iron can be accumulated even during high-affinity uptake.

  1. The Organization of Controller Motifs Leading to Robust Plant Iron Homeostasis

    PubMed Central

    Agafonov, Oleg; Selstø, Christina Helen; Thorsen, Kristian; Xu, Xiang Ming; Drengstig, Tormod; Ruoff, Peter

    2016-01-01

    Iron is an essential element needed by all organisms for growth and development. Because iron becomes toxic at higher concentrations iron is under homeostatic control. Plants face also the problem that iron in the soil is tightly bound to oxygen and difficult to access. Plants have therefore developed special mechanisms for iron uptake and regulation. During the last years key components of plant iron regulation have been identified. How these components integrate and maintain robust iron homeostasis is presently not well understood. Here we use a computational approach to identify mechanisms for robust iron homeostasis in non-graminaceous plants. In comparison with experimental results certain control arrangements can be eliminated, among them that iron homeostasis is solely based on an iron-dependent degradation of the transporter IRT1. Recent IRT1 overexpression experiments suggested that IRT1-degradation is iron-independent. This suggestion appears to be misleading. We show that iron signaling pathways under IRT1 overexpression conditions become saturated, leading to a breakdown in iron regulation and to the observed iron-independent degradation of IRT1. A model, which complies with experimental data places the regulation of cytosolic iron at the transcript level of the transcription factor FIT. Including the experimental observation that FIT induces inhibition of IRT1 turnover we found a significant improvement in the system’s response time, suggesting a functional role for the FIT-mediated inhibition of IRT1 degradation. By combining iron uptake with storage and remobilization mechanisms a model is obtained which in a concerted manner integrates iron uptake, storage and remobilization. In agreement with experiments the model does not store iron during its high-affinity uptake. As an iron biofortification approach we discuss the possibility how iron can be accumulated even during high-affinity uptake. PMID:26800438

  2. Effect of Rasch Calibration on Ability and DIF Estimation in Computer-Adaptive Tests. Research Report RR-94-32.

    ERIC Educational Resources Information Center

    Zwick, Rebecca; And Others

    A previous simulation study of methods for assessing item functioning (DIF) in computer-adaptive tests (CATs) showed that modified versions of the Mantel-Haenszel and standardization methods work well with CAT data. In that study, data were generated using the three-parameter logistic (3PL) model, and this same model was assumed in obtaining item…

  3. Supermatrix models

    SciTech Connect

    Yost, S.A.

    1991-05-01

    Radom matrix models based on an integral over supermatrices are proposed as a natural extension of bosonic matrix models. The subtle nature of superspace integration allows these models to have very different properties from the analogous bosonic models. Two choices of integration slice are investigated. One leads to a perturbative structure which is reminiscent of, and perhaps identical to, the usual Hermitian matrix models. Another leads to an eigenvalue reduction which can be described by a two component plasma in one dimension. A stationary point of the model is described.

  4. Simple imputation methods versus direct likelihood analysis for missing item scores in multilevel educational data.

    PubMed

    Kadengye, Damazo T; Cools, Wilfried; Ceulemans, Eva; Van den Noortgate, Wim

    2012-06-01

    Missing data, such as item responses in multilevel data, are ubiquitous in educational research settings. Researchers in the item response theory (IRT) context have shown that ignoring such missing data can create problems in the estimation of the IRT model parameters. Consequently, several imputation methods for dealing with missing item data have been proposed and shown to be effective when applied with traditional IRT models. Additionally, a nonimputation direct likelihood analysis has been shown to be an effective tool for handling missing observations in clustered data settings. This study investigates the performance of six simple imputation methods, which have been found to be useful in other IRT contexts, versus a direct likelihood analysis, in multilevel data from educational settings. Multilevel item response data were simulated on the basis of two empirical data sets, and some of the item scores were deleted, such that they were missing either completely at random or simply at random. An explanatory IRT model was used for modeling the complete, incomplete, and imputed data sets. We showed that direct likelihood analysis of the incomplete data sets produced unbiased parameter estimates that were comparable to those from a complete data analysis. Multiple-imputation approaches of the two-way mean and corrected item mean substitution methods displayed varying degrees of effectiveness in imputing data that in turn could produce unbiased parameter estimates. The simple random imputation, adjusted random imputation, item means substitution, and regression imputation methods seemed to be less effective in imputing missing item scores in multilevel data settings.

  5. Does what you know matter? Investigating the relationship between mental models of climate change and pro-environmental behaviors

    NASA Astrophysics Data System (ADS)

    Davis, R.

    2013-12-01

    demographic questions; three discreet instruments measuring (1) mental models of climate change, (2) attitudes and beliefs about climate change, and (3) self-reported behaviors; and an experimental intervention, followed by a behavioral intention question. Latent class analysis (LCA) and item-response theory (IRT) will be employed to analyze multiple-choice responses to the mental model survey to create groupings of individuals assumed to hold similar mental of climate change. A principal component analysis (PCA) using oblique rotation was employed to identify five scales (Chronbach's alpha > 0.80) within the attitude/belief instrument. Total and sub-scale scores were also calculated for self-reported behaviors. The relationships between mental models, attitudes and behaviors will be analyzed using multiple regression models. This work presents not only the development and validation of three novel instruments for accurately and efficiently measuring mental models, attitudes, and self-reported behaviors, but also provides insight into the types of mental models individuals hold. Understanding how climate change is conceptualized and how such knowledge influences attitudes and behaviors gives educators tools for guiding students towards more expert understandings while also enabling environmentalists to craft more effective messages.

  6. ENTRAINMENT MODELS

    EPA Science Inventory

    This presentation presented information on entrainment models. Entrainment models use entrainment hypotheses to express the continuity equation. The advantage is that plume boundaries are known. A major disadvantage is that the problems that can be solved are rather simple. The ...

  7. Radiation Models

    ERIC Educational Resources Information Center

    James, W. G. G.

    1970-01-01

    Discusses the historical development of both the wave and the corpuscular photon model of light. Suggests that students should be informed that the two models are complementary and that each model successfully describes a wide range of radiation phenomena. Cites 19 references which might be of interest to physics teachers and students. (LC)

  8. Hydrological models are mediating models

    NASA Astrophysics Data System (ADS)

    Babel, L. V.; Karssenberg, D.

    2013-08-01

    Despite the increasing role of models in hydrological research and decision-making processes, only few accounts of the nature and function of models exist in hydrology. Earlier considerations have traditionally been conducted while making a clear distinction between physically-based and conceptual models. A new philosophical account, primarily based on the fields of physics and economics, transcends classes of models and scientific disciplines by considering models as "mediators" between theory and observations. The core of this approach lies in identifying models as (1) being only partially dependent on theory and observations, (2) integrating non-deductive elements in their construction, and (3) carrying the role of instruments of scientific enquiry about both theory and the world. The applicability of this approach to hydrology is evaluated in the present article. Three widely used hydrological models, each showing a different degree of apparent physicality, are confronted to the main characteristics of the "mediating models" concept. We argue that irrespective of their kind, hydrological models depend on both theory and observations, rather than merely on one of these two domains. Their construction is additionally involving a large number of miscellaneous, external ingredients, such as past experiences, model objectives, knowledge and preferences of the modeller, as well as hardware and software resources. We show that hydrological models convey the role of instruments in scientific practice by mediating between theory and the world. It results from these considerations that the traditional distinction between physically-based and conceptual models is necessarily too simplistic and refers at best to the stage at which theory and observations are steering model construction. The large variety of ingredients involved in model construction would deserve closer attention, for being rarely explicitly presented in peer-reviewed literature. We believe that devoting

  9. Model Experiments and Model Descriptions

    NASA Technical Reports Server (NTRS)

    Jackman, Charles H.; Ko, Malcolm K. W.; Weisenstein, Debra; Scott, Courtney J.; Shia, Run-Lie; Rodriguez, Jose; Sze, N. D.; Vohralik, Peter; Randeniya, Lakshman; Plumb, Ian

    1999-01-01

    The Second Workshop on Stratospheric Models and Measurements Workshop (M&M II) is the continuation of the effort previously started in the first Workshop (M&M I, Prather and Remsberg [1993]) held in 1992. As originally stated, the aim of M&M is to provide a foundation for establishing the credibility of stratospheric models used in environmental assessments of the ozone response to chlorofluorocarbons, aircraft emissions, and other climate-chemistry interactions. To accomplish this, a set of measurements of the present day atmosphere was selected. The intent was that successful simulations of the set of measurements should become the prerequisite for the acceptance of these models as having a reliable prediction for future ozone behavior. This section is divided into two: model experiment and model descriptions. In the model experiment, participant were given the charge to design a number of experiments that would use observations to test whether models are using the correct mechanisms to simulate the distributions of ozone and other trace gases in the atmosphere. The purpose is closely tied to the needs to reduce the uncertainties in the model predicted responses of stratospheric ozone to perturbations. The specifications for the experiments were sent out to the modeling community in June 1997. Twenty eight modeling groups responded to the requests for input. The first part of this section discusses the different modeling group, along with the experiments performed. Part two of this section, gives brief descriptions of each model as provided by the individual modeling groups.

  10. Two iron-regulated cation transporters from tomato complement metal uptake-deficient yeast mutants.

    PubMed

    Eckhardt, U; Mas Marques, A; Buckhout, T J

    2001-03-01

    Although iron deficiency poses severe nutritional problems to crop plants, to date iron transporters have only been characterized from the model plant Arabidopsis thaliana. To extend our molecular knowledge of Fe transport in crop plants, we have isolated two cDNAs (LeIRT1 and LeIRT2) from a library constructed from roots of iron-deficient tomato (Lycopersicon esculentum) plants, using the Arabidopsis iron transporter cDNA, IRTI, as a probe. Their deduced polypeptides display 64% and 62% identical amino acid residues to the IRT1 protein, respectively. Transcript level analyses revealed that both genes were predominantly expressed in roots. Transcription of LeIRT2 was unaffected by the iron status of the plant, while expression of LeIRT1 was strongly enhanced by iron limitation. The growth defect of an iron uptake-deficient yeast (Saccharomyces cerevisiae) mutant was complemented by LeIRT1 and LeIRT2 when ligated to a yeast expression plasmid. Transport assays revealed that iron uptake was restored in the transformed yeast cells. This uptake was temperature-dependent and saturable, and Fe2+ rather than Fe3+ was the preferred substrate. A number of divalent metal ions inhibited Fe2+ uptake when supplied at 100-fold or 10-fold excess. Manganese, zinc and copper uptake-deficient yeast mutants were also rescued by the two tomato cDNAs, suggesting that their gene products have a broad substrate range. The gene structure was determined by polymerase chain reaction experiments and, surprisingly, both genes are arranged in tandem with a tail-to-tail orientation.

  11. Full-Information Factor Analysis for Polytomous Item Responses.

    ERIC Educational Resources Information Center

    Muraki, Eiji; Carlson, James E.

    A multidimensional item response theory (IRT) model for polytomously scored items, based on the graded response model and using the normal ogive, is developed; and an EM algorithm that may be used to estimate the parameters of the model is also discussed. The model is illustrated through a simulation study in which the polytomous item responses of…

  12. Climate Models

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.

    2012-01-01

    Climate models is a very broad topic, so a single volume can only offer a small sampling of relevant research activities. This volume of 14 chapters includes descriptions of a variety of modeling studies for a variety of geographic regions by an international roster of authors. The climate research community generally uses the rubric climate models to refer to organized sets of computer instructions that produce simulations of climate evolution. The code is based on physical relationships that describe the shared variability of meteorological parameters such as temperature, humidity, precipitation rate, circulation, radiation fluxes, etc. Three-dimensional climate models are integrated over time in order to compute the temporal and spatial variations of these parameters. Model domains can be global or regional and the horizontal and vertical resolutions of the computational grid vary from model to model. Considering the entire climate system requires accounting for interactions between solar insolation, atmospheric, oceanic and continental processes, the latter including land hydrology and vegetation. Model simulations may concentrate on one or more of these components, but the most sophisticated models will estimate the mutual interactions of all of these environments. Advances in computer technology have prompted investments in more complex model configurations that consider more phenomena interactions than were possible with yesterday s computers. However, not every attempt to add to the computational layers is rewarded by better model performance. Extensive research is required to test and document any advantages gained by greater sophistication in model formulation. One purpose for publishing climate model research results is to present purported advances for evaluation by the scientific community.

  13. A neutronic feasibility study for LEU conversion of the IR-8 research reactor.

    SciTech Connect

    Deen, J. R.

    1998-10-22

    Equilibrium fuel cycle comparisons for the IR-8 research reactor were made for HEU(90%), HEU(36%), and LEU (19.75%) fuel assembly (FA) designs using three dimensional multi-group diffusion theory models benchmarked to detailed Monte Carlo models of the reactor. Comparisons were made of changes in reactivity, cycle length, average {sup 235}U discharge burnup, thermal neutron flux, and control rod worths for the 90% and 36% enriched IRT-3M fuel assembly and the 19.75% enriched IRT-4M fuel assembly with the same fuel management strategy. The results of these comparisons showed that a uranium density of 3.5 g/cm{sup 3} in the fuel meat would be required in the LEU IRT-4M fuel assembly to match the cycle length of the HEU(90%) IRT-3M FA and an LEU density of 3.7 g/cm{sup 3} is needed to match the cycle length of the HEU(36%) IRT-3M FA.

  14. Phenomenological models

    SciTech Connect

    Braby, L.A.

    1990-09-01

    The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. A range of models covering different endpoints and phenomena has developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified. 43 refs., 13 figs.

  15. Cloud Modeling

    NASA Technical Reports Server (NTRS)

    Tao, Wei-Kuo; Moncrieff, Mitchell; Einaud, Franco (Technical Monitor)

    2001-01-01

    Numerical cloud models have been developed and applied extensively to study cloud-scale and mesoscale processes during the past four decades. The distinctive aspect of these cloud models is their ability to treat explicitly (or resolve) cloud-scale dynamics. This requires the cloud models to be formulated from the non-hydrostatic equations of motion that explicitly include the vertical acceleration terms since the vertical and horizontal scales of convection are similar. Such models are also necessary in order to allow gravity waves, such as those triggered by clouds, to be resolved explicitly. In contrast, the hydrostatic approximation, usually applied in global or regional models, does allow the presence of gravity waves. In addition, the availability of exponentially increasing computer capabilities has resulted in time integrations increasing from hours to days, domain grids boxes (points) increasing from less than 2000 to more than 2,500,000 grid points with 500 to 1000 m resolution, and 3-D models becoming increasingly prevalent. The cloud resolving model is now at a stage where it can provide reasonably accurate statistical information of the sub-grid, cloud-resolving processes poorly parameterized in climate models and numerical prediction models.

  16. Ventilation Model

    SciTech Connect

    V. Chipman

    2002-10-05

    The purpose of the Ventilation Model is to simulate the heat transfer processes in and around waste emplacement drifts during periods of forced ventilation. The model evaluates the effects of emplacement drift ventilation on the thermal conditions in the emplacement drifts and surrounding rock mass, and calculates the heat removal by ventilation as a measure of the viability of ventilation to delay the onset of peak repository temperature and reduce its magnitude. The heat removal by ventilation is temporally and spatially dependent, and is expressed as the fraction of heat carried away by the ventilation air compared to the fraction of heat produced by radionuclide decay. One minus the heat removal is called the wall heat fraction, or the remaining amount of heat that is transferred via conduction to the surrounding rock mass. Downstream models, such as the ''Multiscale Thermohydrologic Model'' (BSC 2001), use the wall heat fractions as outputted from the Ventilation Model to initialize their post-closure analyses. The Ventilation Model report was initially developed to analyze the effects of preclosure continuous ventilation in the Engineered Barrier System (EBS) emplacement drifts, and to provide heat removal data to support EBS design. Revision 00 of the Ventilation Model included documentation of the modeling results from the ANSYS-based heat transfer model. The purposes of Revision 01 of the Ventilation Model are: (1) To validate the conceptual model for preclosure ventilation of emplacement drifts and verify its numerical application in accordance with new procedural requirements as outlined in AP-SIII-10Q, Models (Section 7.0). (2) To satisfy technical issues posed in KTI agreement RDTME 3.14 (Reamer and Williams 2001a). Specifically to demonstrate, with respect to the ANSYS ventilation model, the adequacy of the discretization (Section 6.2.3.1), and the downstream applicability of the model results (i.e. wall heat fractions) to initialize post

  17. Model Selection for Geostatistical Models

    SciTech Connect

    Hoeting, Jennifer A.; Davis, Richard A.; Merton, Andrew A.; Thompson, Sandra E.

    2006-02-01

    We consider the problem of model selection for geospatial data. Spatial correlation is typically ignored in the selection of explanatory variables and this can influence model selection results. For example, the inclusion or exclusion of particular explanatory variables may not be apparent when spatial correlation is ignored. To address this problem, we consider the Akaike Information Criterion (AIC) as applied to a geostatistical model. We offer a heuristic derivation of the AIC in this context and provide simulation results that show that using AIC for a geostatistical model is superior to the often used approach of ignoring spatial correlation in the selection of explanatory variables. These ideas are further demonstrated via a model for lizard abundance. We also employ the principle of minimum description length (MDL) to variable selection for the geostatistical model. The effect of sampling design on the selection of explanatory covariates is also explored.

  18. Modeling Sunspots

    ERIC Educational Resources Information Center

    Oh, Phil Seok; Oh, Sung Jin

    2013-01-01

    Modeling in science has been studied by education researchers for decades and is now being applied broadly in school. It is among the scientific practices featured in the "Next Generation Science Standards" ("NGSS") (Achieve Inc. 2013). This article describes modeling activities in an extracurricular science club in a high…

  19. Dispersion Modeling.

    ERIC Educational Resources Information Center

    Budiansky, Stephen

    1980-01-01

    This article discusses the need for more accurate and complete input data and field verification of the various models of air pollutant dispension. Consideration should be given to changing the form of air quality standards based on enhanced dispersion modeling techniques. (Author/RE)

  20. Qualitative modeling.

    PubMed

    Forbus, Kenneth D

    2011-07-01

    Qualitative modeling concerns the representations and reasoning that people use to understand continuous aspects of the world. Qualitative models formalize everyday notions of causality and provide accounts of how to ground symbolic, relational representations in perceptual processes. This article surveys the basic ideas of qualitative modeling and their applications from a cognitive science perspective. It describes the basic principles of qualitative modeling, and a variety of qualitative representations that have been developed for quantities and for relationships between them, providing a kind of qualitative mathematics. Three ontological frameworks for organizing modeling knowledge (processes, components, and field) are summarized, along with research on automatically assembling models for particular tasks from such knowledge. Qualitative simulation and how it carves up time into meaningful units is discussed. We discuss several accounts of causal reasoning about dynamical systems, based on different choices of qualitative mathematics and ontology. Qualitative spatial reasoning is explored, both in terms of relational systems and visual reasoning. Applications of qualitative models of particular interest to cognitive scientists are described, including how they have been used to capture the expertise of scientists and engineers and how they have been used in education. Open questions and frontiers are also discussed, focusing on relationships between ideas developed in the qualitative modeling community and other areas of cognitive science. WIREs Cogni Sci 2011 2 374-391 DOI: 10.1002/wcs.115 For further resources related to this article, please visit the WIREs website.

  1. Turbulence modeling

    NASA Technical Reports Server (NTRS)

    Bardina, Jorge E.

    1995-01-01

    The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.

  2. Climate models and model evaluation

    SciTech Connect

    Gates, W.L.

    1994-12-31

    This brief overview addresses aspects of the nature, uses, evaluation and limitations of climate models. A comprehensive global modeling capability has been achieved only for the physical climate system, which is characterized by processes that serve to transport and exchange momentum, heat and moisture within and between the atmosphere, ocean and land surface. The fundamental aim of climate modeling, and the justification for the use of climate models, is the need to achieve a quantitative understanding of the operation of the climate system and to exploit any potential predictability that may exist.

  3. OSPREY Model

    SciTech Connect

    Veronica J. Rutledge

    2013-01-01

    The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and REcoverY (OSPREY) models the adsorption of off-gas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data is obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data and parameters were input into the adsorption model to develop models specific for krypton adsorption. The same can be done for iodine, xenon, and tritium. The model will be validated with experimental breakthrough curves. Customers will be given access to

  4. Model hydrographs

    USGS Publications Warehouse

    Mitchell, W.D.

    1972-01-01

    Model hydrographs are composed of pairs of dimensionless ratios, arrayed in tabular form, which, when modified by the appropriate values of rainfall exceed and by the time and areal characteristics of the drainage basin, satisfactorily represent the flood hydrograph for the basin. Model bydrographs are developed from a dimensionless translation hydrograph, having a time base of T hours and appropriately modified for storm duration by routing through reservoir storage, S=kOx. Models fall into two distinct classes: (1) those for which the value of x is unity and which have all the characteristics of true unit hydrographs and (2) those for which the value of x is other than unity and to which the unit-hydrograph principles of proportionality and superposition do not apply. Twenty-six families of linear models and eight families of nonlinear models in tabular form from the principal subject of this report. Supplemental discussions describe the development of the models and illustrate their application. Other sections of the report, supplemental to the tables, describe methods of determining the hydrograph characteristics, T, k, and x, both from observed hydrograph and from the physical characteristics of the drainage basin. Five illustrative examples of use show that the models, when properly converted to incorporate actual rainfall excess and the time and areal characteristics of the drainage basins, do indeed satisfactorily represent the observed flood hydrographs for the basins.

  5. Stereometric Modelling

    NASA Astrophysics Data System (ADS)

    Grimaldi, P.

    2012-07-01

    These mandatory guidelines are provided for preparation of papers accepted for publication in the series of Volumes of The The stereometric modelling means modelling achieved with : - the use of a pair of virtual cameras, with parallel axes and positioned at a mutual distance average of 1/10 of the distance camera-object (in practice the realization and use of a stereometric camera in the modeling program); - the shot visualization in two distinct windows - the stereoscopic viewing of the shot while modelling. Since the definition of "3D vision" is inaccurately referred to as the simple perspective of an object, it is required to add the word stereo so that "3D stereo vision " shall stand for "three-dimensional view" and ,therefore, measure the width, height and depth of the surveyed image. Thanks to the development of a stereo metric model , either real or virtual, through the "materialization", either real or virtual, of the optical-stereo metric model made visible with a stereoscope. It is feasible a continuous on line updating of the cultural heritage with the help of photogrammetry and stereometric modelling. The catalogue of the Architectonic Photogrammetry Laboratory of Politecnico di Bari is available on line at: http://rappresentazione.stereofot.it:591/StereoFot/FMPro?-db=StereoFot.fp5&-lay=Scheda&-format=cerca.htm&-view

  6. Robustness of Value-Added Analysis of School Effectiveness. Research Report. ETS RR-08-22

    ERIC Educational Resources Information Center

    Braun, Henry; Qu, Yanxuan

    2008-01-01

    This paper reports on a study conducted to investigate the consistency of the results between 2 approaches to estimating school effectiveness through value-added modeling. Estimates of school effects from the layered model employing item response theory (IRT) scaled data are compared to estimates derived from a discrete growth model based on the…

  7. The Effects of Rater Severity and Rater Distribution on Examinees' Ability Estimation for Constructed-Response Items. Research Report. ETS RR-13-23

    ERIC Educational Resources Information Center

    Wang, Zhen; Yao, Lihua

    2013-01-01

    The current study used simulated data to investigate the properties of a newly proposed method (Yao's rater model) for modeling rater severity and its distribution under different conditions. Our study examined the effects of rater severity, distributions of rater severity, the difference between item response theory (IRT) models with rater effect…

  8. A Model for Math Modeling

    ERIC Educational Resources Information Center

    Lin, Tony; Erfan, Sasan

    2016-01-01

    Mathematical modeling is an open-ended research subject where no definite answers exist for any problem. Math modeling enables thinking outside the box to connect different fields of studies together including statistics, algebra, calculus, matrices, programming and scientific writing. As an integral part of society, it is the foundation for many…

  9. Anchor Modeling

    NASA Astrophysics Data System (ADS)

    Regardt, Olle; Rönnbäck, Lars; Bergholtz, Maria; Johannesson, Paul; Wohed, Petia

    Maintaining and evolving data warehouses is a complex, error prone, and time consuming activity. The main reason for this state of affairs is that the environment of a data warehouse is in constant change, while the warehouse itself needs to provide a stable and consistent interface to information spanning extended periods of time. In this paper, we propose a modeling technique for data warehousing, called anchor modeling, that offers non-destructive extensibility mechanisms, thereby enabling robust and flexible management of changes in source systems. A key benefit of anchor modeling is that changes in a data warehouse environment only require extensions, not modifications, to the data warehouse. This ensures that existing data warehouse applications will remain unaffected by the evolution of the data warehouse, i.e. existing views and functions will not have to be modified as a result of changes in the warehouse model.

  10. Programming models

    SciTech Connect

    Daniel, David J; Mc Pherson, Allen; Thorp, John R; Barrett, Richard; Clay, Robert; De Supinski, Bronis; Dube, Evi; Heroux, Mike; Janssen, Curtis; Langer, Steve; Laros, Jim

    2011-01-14

    A programming model is a set of software technologies that support the expression of algorithms and provide applications with an abstract representation of the capabilities of the underlying hardware architecture. The primary goals are productivity, portability and performance.

  11. Model Lungs.

    ERIC Educational Resources Information Center

    Taylor, Emma

    1991-01-01

    A cheap and simple model that can be made and used by pupils to study the human breathing mechanism is presented. A list of needed materials, procedures for construction, possible refinements, and method of use are included. (KR)

  12. Micromolecular modeling

    NASA Technical Reports Server (NTRS)

    Guillet, J. E.

    1984-01-01

    A reaction kinetics based model of the photodegradation process, which measures all important rate constants, and a computerized model capable of predicting the photodegradation rate and failure modes of a 30 year period, were developed. It is shown that the computerized photodegradation model for polyethylene correctly predicts failure of ELVAX 15 and cross linked ELVAX 150 on outdoor exposure. It is indicated that cross linking ethylene vinyl acetate (EVA) does not significantly change its degradation rate. It is shown that the effect of the stabilizer package is approximately equivalent on both polymers. The computerized model indicates that peroxide decomposers and UV absorbers are the most effective stabilizers. It is found that a combination of UV absorbers and a hindered amine light stabilizer (HALS) is the most effective stabilizer system.

  13. Environmental Modeling

    EPA Pesticide Factsheets

    EPA's modeling community is working to gain insights into certain parts of a physical, biological, economic, or social system by conducting environmental assessments for Agency decision making to complex environmental issues.

  14. Energy Models

    EPA Science Inventory

    Energy models characterize the energy system, its evolution, and its interactions with the broader economy. The energy system consists of primary resources, including both fossil fuels and renewables; power plants, refineries, and other technologies to process and convert these r...

  15. PREDICTIVE MODELS

    SciTech Connect

    Ray, R.M. )

    1986-12-01

    PREDICTIVE MODELS is a collection of five models - CFPM, CO2PM, ICPM, PFPM, and SFPM - used in the 1982-1984 National Petroleum Council study of enhanced oil recovery (EOR) potential. Each pertains to a specific EOR process designed to squeeze additional oil from aging or spent oil fields. The processes are: 1) chemical flooding, where soap-like surfactants are injected into the reservoir to wash out the oil; 2) carbon dioxide miscible flooding, where carbon dioxide mixes with the lighter hydrocarbons making the oil easier to displace; 3) in-situ combustion, which uses the heat from burning some of the underground oil to thin the product; 4) polymer flooding, where thick, cohesive material is pumped into a reservoir to push the oil through the underground rock; and 5) steamflood, where pressurized steam is injected underground to thin the oil. CFPM, the Chemical Flood Predictive Model, models micellar (surfactant)-polymer floods in reservoirs, which have been previously waterflooded to residual oil saturation. Thus, only true tertiary floods are considered. An option allows a rough estimate of oil recovery by caustic or caustic-polymer processes. CO2PM, the Carbon Dioxide miscible flooding Predictive Model, is applicable to both secondary (mobile oil) and tertiary (residual oil) floods, and to either continuous CO2 injection or water-alternating gas processes. ICPM, the In-situ Combustion Predictive Model, computes the recovery and profitability of an in-situ combustion project from generalized performance predictive algorithms. PFPM, the Polymer Flood Predictive Model, is switch-selectable for either polymer or waterflooding, and an option allows the calculation of the incremental oil recovery and economics of polymer relative to waterflooding. SFPM, the Steamflood Predictive Model, is applicable to the steam drive process, but not to cyclic steam injection (steam soak) processes.

  16. Model selection for geostatistical models.

    PubMed

    Hoeting, Jennifer A; Davis, Richard A; Merton, Andrew A; Thompson, Sandra E

    2006-02-01

    We consider the problem of model selection for geospatial data. Spatial correlation is often ignored in the selection of explanatory variables, and this can influence model selection results. For example, the importance of particular explanatory variables may not be apparent when spatial correlation is ignored. To address this problem, we consider the Akaike Information Criterion (AIC) as applied to a geostatistical model. We offer a heuristic derivation of the AIC in this context and provide simulation results that show that using AIC for a geostatistical model is superior to the often-used traditional approach of ignoring spatial correlation in the selection of explanatory variables. These ideas are further demonstrated via a model for lizard abundance. We also apply the principle of minimum description length (MDL) to variable selection for the geostatistical model. The effect of sampling design on the selection of explanatory covariates is also explored. R software to implement the geostatistical model selection methods described in this paper is available in the Supplement.

  17. Scalable Models Using Model Transformation

    DTIC Science & Technology

    2008-07-13

    huge number of web documents. We have created a simplified demo using 5 worker machines in the Ptolemy II modeling and simulation environment [3], as...the pattern of the transformation rule matches any subgraph of the input model. When the TransformationRule actor is opened in the Ptolemy II GUI...tool developed in the Ptolemy II frame- work, existing tools include AGG [14], PROGRES [15], AToM3 [16], FUJABA [17], VIATRA2 [18], and GReAT [19

  18. Modeling reality

    NASA Technical Reports Server (NTRS)

    Denning, Peter J.

    1990-01-01

    Although powerful computers have allowed complex physical and manmade hardware systems to be modeled successfully, we have encountered persistent problems with the reliability of computer models for systems involving human learning, human action, and human organizations. This is not a misfortune; unlike physical and manmade systems, human systems do not operate under a fixed set of laws. The rules governing the actions allowable in the system can be changed without warning at any moment, and can evolve over time. That the governing laws are inherently unpredictable raises serious questions about the reliability of models when applied to human situations. In these domains, computers are better used, not for prediction and planning, but for aiding humans. Examples are systems that help humans speculate about possible futures, offer advice about possible actions in a domain, systems that gather information from the networks, and systems that track and support work flows in organizations.

  19. Extending item response theory to online homework

    NASA Astrophysics Data System (ADS)

    Kortemeyer, Gerd

    2014-06-01

    Item response theory (IRT) becomes an increasingly important tool when analyzing "big data" gathered from online educational venues. However, the mechanism was originally developed in traditional exam settings, and several of its assumptions are infringed upon when deployed in the online realm. For a large-enrollment physics course for scientists and engineers, the study compares outcomes from IRT analyses of exam and homework data, and then proceeds to investigate the effects of each confounding factor introduced in the online realm. It is found that IRT yields the correct trends for learner ability and meaningful item parameters, yet overall agreement with exam data is moderate. It is also found that learner ability and item discrimination is robust over a wide range with respect to model assumptions and introduced noise. Item difficulty is also robust, but over a narrower range.

  20. Overview of the Icing and Flow Quality Improvements Program for the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Irvine, Thomas B.; Kevdzija, Susan L.; Sheldon, David W.; Spera, David A.

    2001-01-01

    Major upgrades were made in 1999 to the 6- by 9-Foot (1.8- by 2.7-m) Icing Research Tunnel (IRT) at the NASA Glenn Research Center. These included replacement of the electronic controls for the variable-speed drive motor, replacement of the heat exchanger, complete replacement and enlargement of the leg of the tunnel containing the new heat-exchanger, the addition of flow-expanding and flow-contracting turning vanes upstream and downstream of the heat exchanger, respectively, and the addition of fan outlet guide vanes (OGV's). This paper describes the rationale behind this latest program of IRT upgrades and the program's requirements and goals. An overview is given of the scope of work undertaken by the design and construction contractors, the scale-model IRT (SMIRT) design verification program, the comprehensive reactivation test program initiated upon completion of construction, and the overall management approach followed.