Mohammad Salehi - Sharif University of Technology
Alireza Tayebi - Sharif University of Technology

Validation is an important enterprise especially when a test is a high stakes one. Demographic variables like gender and field of study can affect test results and interpretations. Differential Item Functioning (DIF) is a way to make sure that a test does not favor one group of test takers over the others. This study investigated DIF in terms of gender in the reading comprehension subtest (۳۵ items) of a high stakes test using a three-step logistic regression procedure (Zumbo, ۱۹۹۹). The participants of the study were ۳,۳۹۸ test takers, both males and females, who took the test in question (the UTEPT) as a partial requirement for entering a PhD program at the University of Tehran. To show whether the ۳۵ items of the reading comprehension part exhibited DIF or not, logistic regression using a three step procedure (Zumbo, ۱۹۹۹) was employed. Three sets of criteria of Cohen’s (۱۹۸۸), Zumbo’s (۱۹۹۹), and Jodin and Girel’s (۲۰۰۱) were selected. It was revealed that, though the ۳۵ items show “small” effect sizes according to Cohen’s classification, they do not display DIF based on the other two criteria. Therefore, it can be concluded that the reading comprehension subtest of the UTEPT favors neither males nor females.     

validity, Test validation, Test fairness, Differential Item Functioning (DIF), Logistic Regression (LR), Item response Theory (IRT)