Exploring Aberrant Responses Using Person Fit and Person Response Functions.

Person fit statistics provide equivocal interpretations regarding aberrant responses. This study uses person response functions (PRF) to supplement the interpretation of person fit statistics. Sixty-three multiple-choice items were administered to a sample of persons (N=31) who used guessing strategies to answer them. After answering each item, participants indicated which guessing strategy they used. The data were analyzed with a Rasch (1960) model, where the item calibrations were anchored to values obtained when the items were appropriately administered. The participants showed poor model-data fit as expected. Further examination of person misfit using person response functions suggests that PRF can provide information about absolute person fit to a model, whereas fit statistics provide information about relative fit, given the other persons in the testing group. PRF can also provide information about where and how person responses misfit the model. This additional information can assist practitioners in using and interpreting individual scores appropriately.