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.

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

Rasch Books and Publications
Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, 2nd Edn. George Engelhard, Jr. & Jue Wang	Applying the Rasch Model (Winsteps, Facets) 4th Ed., Bond, Yan, Heene	Advances in Rasch Analyses in the Human Sciences (Winsteps, Facets) 1st Ed., Boone, Staver	Advances in Applications of Rasch Measurement in Science Education, X. Liu & W. J. Boone	Rasch Analysis in the Human Sciences (Winsteps) Boone, Staver, Yale
Introduction to Many-Facet Rasch Measurement (Facets), Thomas Eckes	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	Appliquer le modèle de Rasch: Défis et pistes de solution (Winsteps) E. Dionne, S. Béland
Exploring Rating Scale Functioning for Survey Research (R, Facets), Stefanie Wind	Rasch Measurement: Applications, Khine	Winsteps Tutorials - free Facets Tutorials - free	Many-Facet Rasch Measurement (Facets) - free, J.M. Linacre	Fairness, Justice and Language Assessment (Winsteps, Facets), McNamara, Knoch, Fan
Other Rasch-Related Resources: Rasch Measurement YouTube Channel
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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