Detection of Differential Item Functioning via the Credible Intervals and Odds Ratios Methods

Differential item functioning (DIF) analysis is an essential procedure for educational and psychological tests to identify items that exhibit varying degrees of DIF. DIF means that the assumption of measurement invariance is violated, and then test scores are incomparable for individuals of the same ability level from different groups, which substantially threatens test validity. In this paper, we investigated the credible intervals (CI) and odds ratios (OR) methods to detect uniform DIF within the framework of the Rasch model through a series of simulations. The results showed that the CI method performed better than the OR method to identify DIF items under the balanced DIF conditions. However, the CI method yielded inflated false positive rates under the unbalanced DIF conditions. The effectiveness of these two approaches was illustrated with an empirical example.