EASY-DIF

Abstract

Practitioners are increasingly becoming interested in Differential Item Functioning (DIF) forimproving the validity of test and scale interpretations. Among the statistical procedures availableto assess DIF in dichotomous and polytomous items, the Mantel-Haenszel chi-square (1959) andother standardization proceduresmay beparticularly attractive to practitioners.Some of the statis-tics associated with Mantel-Haenszel procedure can be performed using specific software such asEZ-DIF (Waller, 1998), DIFAS (Penfield, 2005), and MH-DIF (Fidalgo, 1994). However, usingthese programs requires being familiar with the statistics of DIF procedures in order to understandoutput. In addition, key characteristics of the Mantel-Haenszel procedures, such as the matchingstrategy (thick or thin), purification of the matching criteria, and so on, are not currently availablein all statistical software packages. As a result, EASY-DIF was developed to provide easy-to-usesoftware for performing the most common and useful MH and standardization procedures, witha view to guiding practitioners through the analyses and helping them interpret the output.EASY-DIFanalyzesuniformandnonuniformDIFforthetotalsampleandseparatelyforlow-performing and high-performing groups (Clauser, Mazor, & Hambleton, 1994). Users canexplore possible cancellation and amplification DIF effects by establishing different cut scoresfor each group. Up to six different matching strategies based on total score distributions can beimplemented: thinmatching,equal interval, percentage of totalsample, percentage of focalsam-ple, censored matching, and minimum cell frequency (Donoghue & Allen, 1993). In addition,users can use a procedure purification of matching criteria through the selection of a validsubtest.For dichotomous items, EASY-DIF computes the Mantel-Haenszel chi-square (Holland T Mantel & Haenszel, 1959), the Mantel-Haenszel common odds ratio (CamilliSMantel&Haenszel,1959),theMH-DeltaDIF,thestandarderrorofMH-DeltaComputer Program Exchange