Applying IRT Model to Determine Gender and Discipline-Based DIF and DDF: A Study of the IAU English Proficiency Test

The purpose of this study was to examine gender and discipline-based Differential Item Functioning (DIF) and Differential Distractor Functioning (DDF) on the Islamic Azad University English Proficiency Test (IAUEPT). The study evaluated DIF and DDF across genders and disciplines using the Rasch model. To conduct DIF and DDF analysis, the examinees were divided into two groups: Humanities and Social Sciences (HSS) and Non-Humanities and Social Sciences (N-HSS). The results of the DIF analysis showed that four out of 100 items had DIF across gender, and two items had discipline DIF. Additionally, gender DDF analysis identified one item each for Options A, B, and C, and four items for Option D. Similarly, the discipline DDF analysis revealed one item for Option A, three items for Option B, four items for Option C, and three items for Option D. The findings of this study have significant implications for test developers. The identification of potential biases in high-stakes proficiency tests can help ensure fairness and equity for all examinees. Furthermore, identifying gender DIF can shed light on potential gender-based gaps in the curriculum, highlighting areas where male or female learners may be disadvantaged or underrepresented in terms of knowledge or skills.