The performance of the three procedures -- the Logistic Regression
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Thissen, Steinberg, & Gerard, 1986), and the Differential Functioning of
Items and Tests procedure (DFIT; Flowers, Oshima, & Raju, 1999) in
detecting differential item functioning (DIF) under the graded response
model (GRM) were compared in a simulation study. Factors manipulated
included sample size, differences in the ability distributions between the
focal and the reference groups, and four different percentages of DIF
items contained in a test. For each of the sixteen combinations, 100
replications of DIF detection were simulated. All three DIF procedures
adhered to nominal Type I error rates under most conditions. LR was the
most powerful among the three under all situations. DFIT was less
powerful than LR, but also useful for DIF detection especially with
groups of different ability distributions and relatively large percentage of
DIF items. Logi, with mean Powers lower than 0.4 in all conditions,
appeared to be sensitive only to items with large DIF size. In addition, the
three procedures were used to assess DIF of the Cognitive Ability
Screening Instrument (CASI) and the results of the DIF analysis were
compared to previous studies.

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