A confirmatory study of Differential Item Functioning on EFL reading comprehension

The present study aimed at investigating DIF sources on an EFL reading comprehension test. Accordingly, 2 DIF detection methods, logistic regression (LR) and item response theory (IRT), were used to flag emergent DIF of 203 (110 females & 93 males) Iranian EFL examinees’ performance on a reading comprehension test. Seven hypothetical DIF sources were examined in this regard: text familiarity, gender, topic/text interest, guessing, and the social variables of location, income, and educational status. Only LR, for gender and text familiarity, could preempt DIF with gender supporting the gendered-text effect while text familiarity benefiting, inversely, the participants with low level of text familiarity. For interest in topic, LR found a single item favoring the group with higher levels of interest and the IRT model detected DIF in either extreme. Regarding guessing and income, the LR indicated DIF supporting the low guessers and high-income group whereas IRT, conversely, showed DIF favoring the high guessers and low-income group. For location and education both methods, correspondingly, demonstrated DIF for the expensive location and educated groups. Finally, the differential test functioning result made it clear that only three sources of DIF (gender, income, & interests) were transferred to the test level. The findings could support a proportional effect of DIF sources.