Sensitivity of the RMSD for detecting item-level misfit in low-performing countries

Jesper Tijmstra*, Maria Bolsinova, Yuan-Ling Liaw, Leslie Rutkowski, David Rutkowski

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Although the root-mean squared deviation (RMSD) is a popular statistical measure for evaluating country-specific item-level misfit (i.e., differential item functioning [DIF]) in international large-scale assessment, this paper shows that its sensitivity to detect misfit may depend strongly on the proficiency distribution of the considered countries. Specifically, items for which most respondents in a country have a very low (or high) probability of providing a correct answer will rarely be flagged by the RMSD as showing misfit, even if very strong DIF is present. With many international large-scale assessment initiatives moving toward covering a more heterogeneous group of countries, this raises issues for the ability of the RMSD to detect item-level misfit, especially in low-performing countries that are not well-aligned with the overall difficulty level of the test. This may put one at risk of incorrectly assuming measurement invariance to hold, and may also inflate estimated between-country difference in proficiency. The degree to which the RMSD is able to detect DIF in low-performing countries is studied using both an empirical example from PISA 2015 and a simulation study.

Original languageEnglish
Number of pages18
JournalJournal of Educational Measurement
DOIs
Publication statusE-pub ahead of print - 2020

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