Differential Items functioning of Mathematics Test of TIMSS 2011 in Grade 8 between Girls and Boys using Item-Response Theory Approach (IRT)

The biggest worry, discussed in tests being inequitable, is the presence of bias possibility or differential functioning. Because bias causes test validity to be suspected and doubted. In this research differential item functioning on the whole 14 blocks of mathematics tests of TIMSS in grade 8 between Iranian girls and boys has been studied using IRT approach. In the order that, first, data have been recoded by SPSS and the assumption of items being unidimensional in all blocks, by NOHARM software have been studied. In the next step the best model that is known as “base model” has been fit for data by BILOG-MG software. In the next process from that base model for studying the items having differential functioning and anchor, IRTLRDIF (Thissen,2001) has been used and at last for final estimation of item and ability parameters, MULTILOG software has been used. Findings show that from 219 items, being studied, of mathematics test in grade 8 of TIMSS 2011, 144 anchor items and 75 items have DIF and items have differential functioning and it is to the loss of girls, the focal group.