Assessing the validity of an IAU General English Achievement Test through hybridizing differential item functioning and differential distractor functioning

Abstract The current study sought to examine the validity of a General English Achievement Test (GEAT), administered university students in fall semester 2018–2019 academic year, by hybridizing differential information (DIF) and distractor function (DDF) analytical models. Using purposive sampling method, from target population undergraduate studying different disciplines at Islamic Azad University (IAU), (Isfahan branch), sample 835 taking GEAT were selected. 60-item multiple-choice test comprised four sub-sections; namely, vocabulary, grammar, cloze test, reading comprehension. students’ scores served as targeted data was examined through application Cochran-Mantel-Haenszel (CMH) multinomial log-linear regression models for detecting DIF DDF, respectively. To account assumption uni-dimensionality, sub-sections analyzed independently. Furthermore, local independence checked based on correlational analysis no extreme values observed. results identified five moderate-level items one DDF item signaling an adverse effect fairness due existing biased items. Notably, these findings may have important implications both language policymakers developers.