Unidimensional Interpretations for Multidimensional Test Items

Kahraman N.

JOURNAL OF EDUCATIONAL MEASUREMENT, vol.50, no.2, pp.227-246, 2013 (SSCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 50 Issue: 2
  • Publication Date: 2013
  • Doi Number: 10.1111/jedm.12012
  • Journal Indexes: Social Sciences Citation Index (SSCI), Scopus
  • Page Numbers: pp.227-246
  • Gazi University Affiliated: No


This article considers potential problems that can arise in estimating a unidimensional item response theory (IRT) model when some test items are multidimensional (i.e., show a complex factorial structure). More specifically, this study examines (1) the consequences of model misfit on IRT item parameter estimates due to unintended minor item-level multidimensionality, and (2) whether a Projection IRT model can provide a useful remedy. A real-data example is used to illustrate the problem and also is used as a base model for a simulation study. The results suggest that ignoring item-level multidimensionality might lead to inflated item discrimination parameter estimates when the proportion of multidimensional test items to unidimensional test items is as low as 1:5. The Projection IRT model appears to be a useful tool for updating unidimensional item parameter estimates of multidimensional test items for a purified unidimensional interpretation.