Removing Rasch Misfit and Cleaning Windows

Question: I must remove nearly 50% of the items to meet the recommended fit criteria. What is wrong with my Rasch analysis?

Reply: Where does misfit end? Imagine you are cleaning a window.

First you see big dirty areas - so you remove the dirt.

Then you see smudges - so you wipe off the smudges.

Then you see scratches - so you polish out the scratches.

Then you see distortions - so you grind out the distortions.

Then you notice discolorations - so you .....

At each stage of a fit analysis, the data are changed so the definition of "good fit" changes. We stop when the measures are "good enough", in the same way as we stop when the window is "clean enough".

One way to verify that the measures are "good enough" is to output the person measures at each stage, and then to cross-plot the person measures for each stage against those of the previous stage. When the difference between the later stage and the earlier stage is too small to matter, or the person measures for a later stage are less meaningful than for an earlier stage (often because there are too few items remaining), then the measures for the earlier stage are "good enough".

Doing this "good enough" procedure, we may discover that the original misfit in the data is too small to have any meaningful impact on the measures. So that no editing of the data is needed.

Linacre J.M. (2010) Removing Rasch Misfit and Cleaning Windows. Rasch Measurement Transactions, 2010, 23:4, 1241

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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
Rasch Books and Publications: Winsteps and Facets
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	Appliquer le modèle de Rasch: Défis et pistes de solution (Winsteps) E. Dionne, S. Béland
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 Facets Tutorials - free	Many-Facet Rasch Measurement (Facets) - free, J.M. Linacre	Fairness, Justice and Language Assessment (Winsteps, Facets), McNamara, Knoch, Fan

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