item parameters
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The study presents statistical procedures that monitor functioning of items over time. We propose generalized likelihood ratio tests that surveil multiple item parameters and implement with various sampling techniques to perform continuous or intermittent monitoring. The procedures examine stability of item parameters across time and inform compromise as soon as they identify significant parameter shift. The performance of the monitoring procedures was validated using simulated and real assessment data. The empirical evaluation suggests that the proposed procedures perform adequately well in identifying the parameter drift. They showed satisfactory detection power and gave timely signals while regulating the error rates reasonably low. The procedures also showed superior performance when compared with the existent methods. The empirical findings suggest that multivariate parametric monitoring can provide an efficient and powerful control tool for maintaining the quality of items. The procedures allow joint monitoring of multiple item parameters and achieve sufficient power by dint of likelihood-ratio tests. Based on the findings from the empirical experimentation, we suggest some practical strategies for performing online item monitoring.

Abstract BackgroundIn the analysis of clinical trial endpoints, calibration of patient-reported outcomes (PRO) instruments ensures that resulting “scores” represent the same quantity of the measured concept between applications. Rasch measurement theory (RMT) is a psychometric approach that guarantees algebraic separation of person and item parameter estimates, allowing formal calibration of PRO instruments. In the RMT framework, calibration is performed using the item parameter estimates obtained from a previous “calibration” study. But if calibration is based on poorly estimated item parameters (e.g., because the sample size of the calibration sample was low), this may hamper the ability to detect a treatment effect, and direct estimation of item parameters from the trial data (non-calibration) may then be preferred. The objective of this simulation study was to assess the impact of calibration on the comparison of PRO results between treatment groups, using different analysis methods.MethodsPRO results were simulated following a polytomous Rasch model, for a calibration and a trial sample. Scenarios included varying sample sizes, with instrument of varying number of items and modalities, and varying item parameters distributions. Different treatment effect sizes and distributions of the two patient samples were also explored. Comparison of treatment groups was performed using different methods based on a random effect Rasch model. Calibrated and non-calibrated approaches were compared based on type-I error, power, bias, and variance of the estimates for the difference between groups.Results There was no impact of the calibration approach on type-I error, power, bias, and dispersion of the estimates. Among other findings, mistargeting between the PRO instrument and patients from the trial sample (regarding the level of measured concept) resulted in a lower power and higher position bias than appropriate targeting. ConclusionsCalibration of PROs in clinical trials does not compromise the ability to accurately assess a treatment effect and is essential to properly interpret PRO results. Given its important added value, calibration should thus always be performed when a PRO instrument is used as an endpoint in a clinical trial, in the RMT framework.

Abstract. To monitor students’ progress and adapt instruction to students’ needs, teachers increasingly use repeated assessments of equivalent tests. The present study investigates whether equivalent reading tests can be successfully developed via rule-based item design. Based on theoretical considerations, we identified 3-item features for reading comprehension at the word, sentence, and text levels, respectively, which should influence the difficulty and time intensity of reading processes. Using optimal design algorithms, a design matrix was calculated, and four equivalent test forms of the German reading test series for second graders (quop-L2) were developed. A total of N = 7,751 students completed the tests. We estimated item difficulty and time intensity parameters as well as person ability and speed parameters using bivariate item response theory (IRT) models, and we investigated the influence of item features on item parameters. Results indicate that all item properties significantly affected either item difficulty or response time. Moreover, as indicated by the IRT-based test information functions and analyses of variance, the four different test forms showed similar levels of difficulty and time-intensity at the word, sentence, and text levels (all η2 < .002). Results were successfully cross-validated using a sample of N = 5,654 students.

To detect differential item functioning (DIF), Rasch trees search for optimal splitpoints in covariates and identify subgroups of respondents in a data-driven way. To determine whether and in which covariate a split should be performed, Rasch trees use statistical significance tests. Consequently, Rasch trees are more likely to label small DIF effects as significant in larger samples. This leads to larger trees, which split the sample into more subgroups. What would be more desirable is an approach that is driven more by effect size rather than sample size. In order to achieve this, we suggest to implement an additional stopping criterion: the popular ETS classification scheme based on the Mantel-Haenszel odds ratio. This criterion helps us to evaluate whether a split in a Rasch tree is based on a substantial or an ignorable difference in item parameters, and it allows the Rasch tree to stop growing when DIF between the identified subgroups is small. Furthermore, it supports identifying DIF items and quantifying DIF effect sizes in each split. Based on simulation results, we conclude that the Mantel-Haenszel effect size further reduces unnecessary splits in Rasch trees under the null hypothesis, or when the sample size is large but DIF effects are negligible. To make the stopping criterion easy-to-use for applied researchers, we have implemented the procedure in the statistical software R. Finally, we discuss how DIF effects between different nodes in a Rasch tree can be interpreted and emphasize the importance of purification strategies for the Mantel-Haenszel procedure on tree stopping and DIF item classification.

Comparative judgment is a method that allows measurement of a competence by comparison of items with other items. In educational measurement, where comparative judgment is becoming an increasingly popular assessment method, items are mostly students’ responses to an assignment or an examination. For assessments using comparative judgment, the Scale Separation Reliability (SSR) is used to estimate the reliability of the measurement. Previous research has shown that the SSR may overestimate reliability when the pairs to be compared are selected with certain adaptive algorithms, when raters use different underlying models/truths, or when the true variance of the item parameters is below one. This research investigated bias and stability of the components of the SSR in relation to the number of comparisons per item to increase understanding of the SSR. We showed that many comparisons are required to obtain an accurate estimate of the item variance, but that the SSR can be useful even when the variance of the items is overestimated. Lastly, we recommend adjusting the general guideline for the required number of comparisons per item to 41 comparisons per item. This recommendation partly depends on the number of items and the true variance in our simulation study and needs further investigation.

When measurement invariance does not hold, researchers aim for partial measurement invariance by identifying anchor items that are assumed to be measurement invariant. In this paper, we build on Bechger and Maris’s approach for identification of anchor items. Instead of identifying differential item functioning (DIF)-free items, they propose to identify different sets of items that are invariant in item parameters within the same item set. We extend their approach by an additional step in order to allow for identification of homogeneously functioning item sets. We evaluate the performance of the extended cluster approach under various conditions and compare its performance to that of previous approaches, that are the equal-mean difficulty (EMD) approach and the iterative forward approach. We show that the EMD and the iterative forward approaches perform well in conditions with balanced DIF or when DIF is small. In conditions with large and unbalanced DIF, they fail to recover the true group mean differences. With appropriate threshold settings, the cluster approach identified a cluster that resulted in unbiased mean difference estimates in all conditions. Compared to previous approaches, the cluster approach allows for a variety of different assumptions as well as for depicting the uncertainty in the results that stem from the choice of the assumption. Using a real data set, we illustrate how the assumptions of the previous approaches may be incorporated in the cluster approach and how the chosen assumption impacts the results.

This article investigates the comparison of two groups based on the two-parameter logistic item response model. It is assumed that there is random differential item functioning in item difficulties and item discriminations. The group difference is estimated using separate calibration with subsequent linking, as well as concurrent calibration. The following linking methods are compared: mean-mean linking, log-mean-mean linking, invariance alignment, Haberman linking, asymmetric and symmetric Haebara linking, different recalibration linking methods, anchored item parameters, and concurrent calibration. It is analytically shown that log-mean-mean linking and mean-mean linking provide consistent estimates if random DIF effects have zero means. The performance of the linking methods was evaluated through a simulation study. It turned out that (log-)mean-mean and Haberman linking performed best, followed by symmetric Haebara linking and a newly proposed recalibration linking method. Interestingly, linking methods frequently found in applications (i.e., asymmetric Haebara linking, recalibration linking used in a variant in current large-scale assessment studies, anchored item parameters, concurrent calibration) perform worse in the presence of random differential item functioning. In line with the previous literature, differences between linking methods turned out be negligible in the absence of random differential item functioning. The different linking methods were also applied in an empirical example that performed a linking of PISA 2006 to PISA 2009 for Austrian students. This application showed that estimated trends in the means and standard deviations depended on the chosen linking method and the employed item response model.

Over the past couple of decades, there has been an increasing interest in adopting ideal point models to represent noncognitive constructs, as they have been demonstrated to better measure typical behaviors than traditional dominance models do. The generalized graded unfolding model ( GGUM) has consistently been the most popular ideal point model among researchers and practitioners. However, the GGUM2004 software and the later developed GGUM package in R can only handle unidimensional models despite the fact that many noncognitive constructs are multidimensional in nature. In addition, GGUM2004 and the GGUM package often yield unreasonable estimates of item parameters and standard errors. To address these issues, we developed the new open-source bmggum R package that is capable of estimating both unidimensional and multidimensional GGUM using a fully Bayesian approach, with supporting capabilities of stabilizing parameterization, incorporating person covariates, estimating constrained models, providing fit diagnostics, producing convergence metrics, and effectively handling missing data.

In the last decade, many R packages were published to perform item response theory (IRT) analysis. Some researchers and practitioners have difficulty in using these functional tools because of their insufficient coding skills. The IRTGUI package provides these researchers a user-friendly GUI where they can perform unidimensional IRT analysis without coding skills. Using the IRTGUI package, person and item parameters, model and item fit indices can be obtained. Dimensionality and local independence assumptions can be tested. With the IRTGUI package, users can generate dichotomous data sets with customizable conditions. Also, Wright Maps, item characteristics and information curves can be graphically displayed. All outputs can be easily downloaded by users.