Identifying Misfitting Achievement Estimates in Performance Assessments: An Illustration Using Rasch and Mokken Scale Analyses

Researchers apply individual person fit analyses as a procedure for checking model-data fit for individual test-takers. When a test-taker misfits, it means that the inferences from their test score regarding what they know and can do may not be accurate. One problem in applying individual person fit procedures in practice is the question of how much misfit it takes to make the test score an untrustworthy estimate of achievement. In this paper, we argue that if a person’s responses generally follow a monotonic pattern, the resulting test score is “good enough” to be interpreted and used. We present an approach that applies statistical procedures from the Rasch and Mokken measurement perspectives to examine individual person fit based on this good enough criterion in real data from a performance assessment. We discuss how these perspectives may facilitate thinking about applying individual person fit procedures in practice.