When to stop removing items and persons in Rasch analysis?

Question: Each time I re-analyze my data after removing a misfitting item or person, another item or person misfits. When do I stop?

Answer: You need to ask yourself a practical question: Why am I removing items and persons? Is this your answer? "To improve the measurement of the persons!"

OK - then here is a strategy. (Look at underfit/high mean-squares before overfit/low mean-squares.)

1. Estimate the person measures from the original analysis. Remove whatever persons and items you see to be really, really bad.

2. Estimate the person measures again. Cross-plot the person measures from 2. against those from 1. Are there any noticeable changes that matter to you?

No. Then the really, really bad wasn't so bad after all. Keep everything. Analysis 1 is what you want.

Yes. Now remove the really bad persons and items.

3. Estimate the person measures again. Cross-plot the person measures from 3. against those from 2. Are there any noticeable changes that matter to you?

No. Then the really bad wasn't so bad after all. Analysis 2 is what you want.

Yes. Now remove the somewhat bad.

4. Estimate the person measures again. Cross-plot the person measures from 4. against those from 3. Are there any noticeable changes that matter to you?

No. Then the somewhat bad wasn't so bad after all. Analysis 3 is what you want. Stop here.

Yes. ..... (and so on)

If you must report all the persons or items, anchor (fix) the good measures at their final good values. Reinstate everything that you need to. Reanalyze and do your final reporting. The good items and person are anchored so that the bad stuff will not distort their measures.

You may discover that the conventional fit criteria are much too strict and are strongly influenced by the misfit of only a few observations.

Later: "removing the misfitting items only improved the results in the case of severe multidimensionality and large proportion of misfitting items, and deteriorated them otherwise."
in "Investigating the Practical Consequences of Model Misfit in Unidimensional IRT Models", Daniela R. Crisan, Jorge N. Tendeiro, Rob R. Meijer, Applied Psychological Measurement, 41, 6, 439-455, July 2017

Linacre J.M. (2010) When to stop removing items and persons in Rasch misfit analysis?, Rasch Measurement Transactions, 2010, 23:4, 1241

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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