A simulation study of item bias using a two-parameter item response model

Possible underlying causes of item bias were examined using a simulation procedure. Data sets were generated to conform to specified factor structures and mean factor scores. Comparisons between the item parameters of various data sets were made with one data set representing the "majority" group and another data set representing the "minority" group. Results indicated that items that required a secondary ability, on which two groups differed in mean level, were generally more biased than those items that do not require a secondary ability. Items with different factor structures in two groups were not consistently identified as more biased than those having similar factor structures. A substantial amount of agreement was found among the bias indices used in the study