Identification of Differential Item Functioning Using Item Response Theory and the Likelihood-Based Model Comparison Approach

Abstract

An important part of examining the adequacy of measures for use in ethnically diverse populations is the evaluation of differential item functioning (DIF) among subpopulations such as those administered the measure in different languages. A number of methods exist for this purpose. The objective of this study was to introduce and demonstrate the identification of DIF using item response theory (IRT) and the likelihood-based model comparison approach. Data come from a sample of community-residing elderly who were part of a dementia case registry. A total of 1578 participants were administered either an English (n = 913) or Spanish (n = 665) version of the 21-item Mini-Mental State Examination. IRT was used to identify language DIF in these items with the likelihood-based model comparison approach. : Fourteen of the 21 items exhibited significant DIF according to language of administration. However, because the direction of the identified DIF was not consistent for one language version over the other, the impact at the scale level was negligible. IRT and the likelihood-based model comparison approach comprise a powerful tool for DIF detection that can aid in the development, refinement, and evaluation of measures for use in ethnically diverse populations.