What to Do about Missing Data?

Ludlow and O'Leary (1999) state: "Missing data occur for a variety of reasons. Particularly problematic are those items an individual skipped or could not reach in time."

They go on to discuss four strategies:

(1) Omitted and not-reached items treated as not administered. This strategy may encourage students to respond only to items they are absolutely sure they will get correct.

(2) Omitted and not-reached items treated as incorrect. This encourages guessing and penalizes slow, careful work.

(3) Omitted items treated as incorrect and not-reached items treated as not administered. This encourages "guess rather than omit", but then "stop when it looks like the test is getting too hard."

(4) First, students are instructed to attempt every question. Then, for item calibration, omitted items treated as incorrect and not-reached items treated as not administered. The items are now anchored, and for person calibration, omitted and not-reached items treated as incorrect. This was adopted for TIMSS.

[This compromise pleases no one, but appears to match American testwiseness more closely than it does the caution expected in traditionalist cultures.]

Ludlow and O'Leary conclude: "The notion of a single, best approach exists in theory only, and suggested courses of action must be evaluated on a number of levels. ... Common sense and reasonable explanations still must govern decisions regarding how test data are analyzed and reported."

Ludlow, L.H., & O'Leary, M. (1999) Scoring omitted and not- reached items: practical data analysis implications. Educational and Psychological Measurement, 59, 4, 615- 603.

Note: though choices as to how to handle missing data must be made by all analysts, it is a testimony to the fundamental strength of Rasch that the precise choice usually has little impact on the measurement framework. The NFER-Nelson plot below, produced independently using their own data, indicates that their item calibrations are essentially equivalent under any reasonable "missing data" strategy.

What to Do about Missing Data? Ludlow, L., & O'Leary, M. … Rasch Measurement Transactions, 2000, 14:2 p.751

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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