Assessing Differential Item Functioning (DIF) For Pearson Test of English (PTE) a study of Test Takers with Different Fields of Study

Abstract

Differential Item Functioning (DIF), which is a statistical feature of an item and provides a sign of unpredicted performance of items on a test, occurs once dissimilar groups of test takers with the same level of ability show different performance on a single test. The aim of this paper was to examine DIF on the Pearson Test of English (PTE) test items. To that end, 250 intermediate EFL learners with the age range of 26 - 36 in two different fields of study (125, Engineering, and 125 Sciences) were randomly chosen for the analysis. The Item Response Theory (IRT) Likelihood Ratio (LR) approach was utilized to find items showing DIF. The scored items of 250 PTE test takers were analyzed using the IRT three-parameter model utilizing item difficulty (b parameter), item discrimination (a parameter), and pseudo-guessing (c parameter). The results of the independent samples t-test for comparison of means in two groups depicted that Science participants performed better than the Engineering ones particularly in Speaking & Writing and Reading sections. It is evident that the PTE test was statistically easier for the Science students at 0.05 level. Linguistic analyses of Differential Item Functioning items also confirmed the findings of the quantitative part, indicating a far better performance on the part of Science students.