A Description and Demonstration of the Polytomous-DFIT Framework

Raju, van der Linden, & Fleer (1995) proposed an item response theory based, parametric differential item functioning (DIF) and differential test functioning (DTF) procedure known as differential functioning of items and tests (DFIT). According to Raju et al., the DFIT framework can be used with unidimensional and multidimensional data that are scored dichotomously and/or polytomously. This study examined the polytomous-DFIT framework. Factors manipulated in the simulation were: (1) length of test (20 and 40 items), (2) focal group distribution, (3) number of DIF items, (4) direction of DIF, and (5) type of DIF. The findings provided promising results and indicated directions for future research. The polytomous DFIT framework was effective in identifying DTF and DIF for the simulated conditions. The DTF index did not perform as consistently as the DIF index. The findings are similar to those of unidimensional and multidimensional DFIT studies.