Differential Item Functioning in examinations of National Organization of Educational Testing across demographic characteristics of Konkur candidates

According to many experts, entrance examination is the most important test in Iran and demographic characteristics such as gender, region (socio-economic status) and province (language) can affect the performance of participants’ responses to the test items. Controlling for the ability of examinees, if the answers to the test items are the function of demographic characteristics, the test items have Differential Item Functioning (DIF) toward them. The purpose of this investigation is to study Differential Item Functioning of the test items of Entrance Examinations of National Organization of Educational Testing across the demographic characteristics. The research sample consisted of all examinees of a test booklet which included some special exams of the experimental groups of Konkur from 2008 to 2011. Binary logisitic regression was used in order to analyzing DIF. After assuring unidimensionality through NOHARM approach, DIF analysis results indicated that the most number of detected DIF items were related to gender, region (socio-economic status) and province (language) variables respectively, but effect sizes were very small and negligible. Nevertheless, based on current research results, it is recommended that subject matter committees are formed to detect biased items based on final decisions of the committees and will be considered in designing test items in future.