Publication Date


Document Type


Committee Members

Gary Burns (Committee Member), David Lahuis (Advisor), Debra Steele-Johnson (Committee Member)

Degree Name

Master of Science (MS)


This study examined two methods for detecting differential item functioning (DIF): Raju, van der Linden, and Fleer's (1995) differential functioning of items and tests procedure (DFIT) and Thissen, Steinberg, and Wainer's (1988) likelihood ratio test (LRT). The major research questions concerned which test provides the best balance of Type I errors and power and if the tests differ in terms of detecting different types of DIF. Monte Carlo simulations were conducted to address these questions. Equal and unequal sample size conditions were fully crossed with test lengths of 10 and 20 items. In addition, α and β parameters were manipulated in order to simulate DIF. Findings indicate that the DFIT and LRT both had acceptable Type I error rates when sample sizes were equal, but that DFIT produced too many Type I errors when sample sizes were unequal. Overall, the LRT exhibited greater power to detect both α and β parameter DIF than DFIT. However, DFIT was more powerful than LRT when the last two β parameters had DIF as opposed to the extreme β parameters. Therefore, it is recommended under most circumstances to use the LRT for DIF detection, unless there is reason to believe that the DIF is at the high end of the scale.

Page Count


Department or Program

Department of Psychology

Year Degree Awarded