An Investigation of Item Position Effects by Means of IRT-Based Differential Item Functioning Methods

In this study, whether item position effects lead to DIF in the condition where different test booklets are used was investigated. To do this the methods of Lord’s chi-square and Raju’s unsigned area with the 3PL model under with and without item purification were used. When the performance of the methods was compared, it was revealed that generally, the method of Lord’s chi-square identified more items with DIF than did the method of Raju’s unsigned area. The differentiation of the booklets with respect to item position resulted in a higher number of items displaying DIF with item purification conditions. Based on the findings of the present study, to avoid the occurrence of DIF due to item position effects, it is recommended to position the same items across different booklets in similar locations when forming different booklets.