Using Multilevel Logistic Regression to Evaluate Person-Fit in IRT Models

I describe how multilevel logistic regression can be used to assess the consistency of an individual's response pattern with an item response theory measurement model. Specifically, by treating item responses as being nested within individuals, multilevel logistic regression is used to estimate a person-response curve that models how an individual's item endorsement rate decreases as a function of item difficulty. The slope of an individual's person-response curve is used as an indicator of the degree of response consistency or person-fit. I argue that the proposed multilevel modeling approach to person-fit assessment has several potential advantages over traditional techniques. The most important advantage being that the multilevel modeling approach allows explanatory variables to be entered into the model so that the causes of response inconsistency or differential test functioning can be investigated.