Estimating the importance of differential item functioning

Several methods have been proposed to detect differential item functioning (DIF), an item response pattern in which members of different demographic groups have different conditional probabilities of answering a test item correctly, given the same level of ability. In this article, the mixture index of fit, proposed by Rudas, Clogg, and Lindsay (1994), is used to estimate the fraction of the population for which DIF occurs, and this approach is compared to the Mantel-Haenszel (Mantel & Haenszel, 1959) test of DIF developed by Holland (1985; see Holland & Thayer, 1988). The proposed estimation procedure, which is noniterative, can provide information about which portions of the item response data appear to be contributing to DIF.