Type I Error Rates for Generalized Graded Unfolding Model Fit Indices

Type I error rates were examined for several fit indices available in GGUM2000: extensions of Infit, Outfit, Andrich's X(2), and the log-likelihood ratio X(2). Infit and Outfit had Type I error rates much lower than nominal alpha. Andrich's X(2) had Type I error rates much higher than nominal alpha, particularly for shorter tests or larger sample sizes. The log-likelihood X(2) had Type I error rates near or below nominal alpha for small samples or longer tests but had inflated error rates with large samples and shorter tests. For conditions in which the log-likelihood ratio X(2) did not perform well, alternative fit indices or modifications to these procedures should be considered in future studies.