What Counseling Researchers Should Know About Evaluating Person Fit: An Illustration of Person Fit Analysis Based on the Partial Credit Model Using the CES-D Scale

We introduce and demonstrate person fit analysis in the context of counseling research. Person fit is an important but often overlooked component of item response theory (IRT) and Rasch model analyses that has implications for the validity, reliability, and fairness of score interpretations for individual participants. It involves evaluating the degree to which individual person estimates from the model can be appropriately interpreted and used. When person misfit occurs, it may not be appropriate to interpret and use a person’s estimate as an indicator of their location on the construct. We use data from the CESD scale to illustrate person fit analysis techniques that combine numeric and graphical evidence. Counseling researchers can incorporate these techniques into their IRT analyses to inform the interpretation and use of scores for individual participants. We emphasize practical interpretations and uses of person fit techniques that can be applied in counseling research contexts.