Effects of differing item parameters on closed-interval DIF statistics

Abstract

The closed-interval signed area (CSA) and closed-interval unsigned area (CUA) statistics were studied by monte carlo simulation to detect differential item functioning when the reference and focal groups had different parameter distributions. When the pseudo-guessing parameter was varied, the CSA was better able to detectmoderate to large differences between the groups than the CUA. However, the effect of the pseudo-guessing parameter varied depending on item discriminations. Index terms: closed-interval measures, differential item functioning, item response theory, monte carlo simulation, signed area measures, unsigned area measures.