Adopting the Multi-process Approach to Detect Differential Item Functioning in Likert Scales

Abstract

The current study compared the performance of the logistic regression (LR) and the odds ratio (OR) approaches in differential item functioning (DIF) detection in which the three processes of an IRTree model were considered in a five-point response scale. Three sets of binary pseudo items (BPI) were generated to indicate an intention of endorsing the midpoint response, a positive/negative attitude toward an item, and a tendency of using extreme category, respectively. Missing values inevitably appeared in the last two sets of BPI. We manipulated the DIF patterns, the percentages of DIF items, and the purification procedure (with/without). The results suggested that (1) both the LR and OR performed well in detecting DIF when BPI did not include missing values; (2) the OR method generally outperformed the LR method when BPI included missing values; (3) the OR method performed fairly well without a purification procedure, but the purification procedure improved the performance of the LR approach, especially when the number of DIF was large.