A Unified Comparison of IRT-Based Effect Sizes for DIF Investigations

Several marginal effect size (ES) statistics suitable for quantifying the magnitude of differential item functioning (DIF) have been proposed in the area of item response theory; for instance, the Differential Functioning of Items and Tests (DFIT) statistics, signed and unsigned item difference in the sample statistics (SIDS, UIDS, NSIDS, and NUIDS), the standardized indices of impact, and the differential response functioning (DRF) statistics. However, the relationship between these proposed statistics has not been fully discussed, particularly with respect to population parameter definitions and recovery performance across independent samples. To address these issues, this article provides a unified presentation of competing DIF ES definitions and estimators, and evaluates the recovery efficacy of these competing estimators using a set of Monte Carlo simulation experiments. Statistical and inferential properties of the estimators are discussed, as well as future areas of research in this model-based area of bias quantification.