This study investigated possible gender bias on a vocabulary test, using a method suggested by Andrich and Hagquist to detect “real” differential item functioning (DIF). A total of 443 adult ESL learners completed all 228 items of the Peabody Picture Vocabulary Test (PPVT-IV). The 310 female and 133 male participants were assumed to be of equal competence, corresponding to levels B1 and B2 on the Common European Framework of Reference for Languages. Male participants outscored female participants, possibly due to the multiple-choice format and to the fact that most gender-biased questions favored men rather than women. Finally, our analysis process yielded only seven items out of 228 as showing gender DIF, which is much lower than the numbers reported in the literature for ESL tests. This low figure suggests that the high number of gender-related DIF items reported in previous research might be attributed to the use of DIF detecting methods that do not take into account artificial DIF stemming from the cross-contamination of test items.
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