Examining Differential Item Functioning (DIF) For Iranian EFL Test Takers with Different Fields of Study

Differential Item Functioning (DIF) takes place when different groups of test-takers with the same level of ability perform differently on a single test. It means some other factors might arise due to group membership. The object of this article was to examine DIF in the MSRT (MCHE) test items. This is an English proficiency test that comprises a total of 100 questions including listening comprehension (LC), structure and written expressions (SWE), and reading comprehension (RC) sections. To this end, 200 pre-intermediate to intermediate Iranian EFL learners with the age range of 25 to 32 in two different fields of study (100 Humanities and 100 sciences) were randomly selected for the analysis. The Item Response Theory (IRT) Likelihood Ratio (LR) approach was used to identify items displaying DIF. The scored item of 200 test-takers was subjected to the IRT Three-Parameter Model presenting the probability that a randomly selected test taker with an ability of theta (θ) answered an item correctly, using item difficulty (b parameter), item discrimination (a parameter), and pseudo-guessing (c parameter). The results of the independent samples t-test for means comparison of two groups indicated that Science test-takers outperformed the Humanities, especially in SWE and RC sections. It can be inferred that the exam was statistically easier for the Science test-takers at 0.05 level. The findings identified 15 DIF items as well. The implications and suggestions for further studies were also reported.