IDENTIFICATION OF ITEMS THAT SHOW NONUNIFORM DIF

This study compared three procedures-the Mantel-Haenszel (MH), the sim ultaneous item bias (SIB), and the logistic regression (LR) procedures -with respect to their Type I error rates and power to detect nonunifo rm differential item functioning (DIF). Data were simulated to reflect a variety of conditions: The factors manipulated included sample size , ability distribution differences between the focal and the reference groups, proportion of DIF items in the test, DIF effect sizes, and ty pe of item. 384 conditions were studied. Both the SIB and LR procedure s were equally powerful in detecting nonuniform DIF under most conditi ons. The MH procedure was not very effective in identifying nonuniform DIF items that had disordinal interactions. The Type I error rates we re within the expected limits for the MH procedure and were higher tha n expected for the SIB and LR procedures; the SIB results showed an ov erall increase of approximately 1% over the results.