Construct Problems with Descriptive IRT

Items and constructs are in constant tension. Each item is intended to probe an underlying construct, but each item also has idiosyncrasies. Only when items are coerced into a sufficient level of cooperation does a stable construct emerge. The process of coercion includes painstaking item writing, item selection, investigation of misfit statistics and careful consideration of the integrity of the evolving construct as it becomes defined by an emerging item hierarchy.

In its celebration of item idiosyncrasies, IRT abandons the construct. At NCME 1996, Darrell Bock presented a Table of 2-PL (two-parameter logistic model) parameters for 100 spelling items. The 2-PL model parameterizes, as "item discrimination", differential performance on items by high and low performing examinees. Since differential item performance disrupts construct stability, variation in "item discrimination" is identified as misfit in a Rasch analysis.

2PL ogives: spelling items


Allowing each item its own life muddles the construct. ICCs for 5 words from Bock's 100 spelling items are shown in the Figure. Bock reports that these words show good fit to his 2PL model. But the item hierarchy for low performers at -2 contradicts that for high performers at +2. For middle performers at 0, tontine and incredulity are equally easy to spell. But for low performers at -2, tontine was easier to spell than incredulity, while for high performers, tontine was harder to spell than incredulity. Since a clear construct is required in order to know what measures mean, descriptive IRT is not measurement.


Construct problems with descriptive IRT. Wright BD, Bock RD. … Rasch Measurement Transactions, 1996, 10:1 p.481



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Rasch Measurement Transactions & Rasch Measurement research papers - free An Introduction to the Rasch Model with Examples in R (eRm, etc.), Debelak, Strobl, Zeigenfuse Rasch Measurement Theory Analysis in R, Wind, Hua Applying the Rasch Model in Social Sciences Using R, Lamprianou El modelo métrico de Rasch: Fundamentación, implementación e interpretación de la medida en ciencias sociales (Spanish Edition), Manuel González-Montesinos M.
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch Rasch Models for Measurement, David Andrich Constructing Measures, Mark Wilson Best Test Design - free, Wright & Stone
Rating Scale Analysis - free, Wright & Masters
Virtual Standard Setting: Setting Cut Scores, Charalambos Kollias Diseño de Mejores Pruebas - free, Spanish Best Test Design A Course in Rasch Measurement Theory, Andrich, Marais Rasch Models in Health, Christensen, Kreiner, Mesba Multivariate and Mixture Distribution Rasch Models, von Davier, Carstensen
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Introduction to Many-Facet Rasch Measurement (Facets), Thomas Eckes Rasch Models for Solving Measurement Problems (Facets), George Engelhard, Jr. & Jue Wang Statistical Analyses for Language Testers (Facets), Rita Green Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments (Facets), George Engelhard, Jr. & Stefanie Wind Aplicação do Modelo de Rasch (Português), de Bond, Trevor G., Fox, Christine M
Exploring Rating Scale Functioning for Survey Research (R, Facets), Stefanie Wind Rasch Measurement: Applications, Khine Winsteps Tutorials - free
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