An Examination of Item Response Theory Item Fit Indices for the Graded Response Model

The current study examined the Type I error rates and power of several item response theory (IRT) item fit indices used in conjunction with the graded response model (GRM). Specifically, S - chi(2), chi(2*), and adjusted chi(2) degrees of freedom ratios (chi(2)/dfs) were examined. Model misfit was introduced by manipulating item parameters and by using a different IRT model to generate item data. Results indicated lower than expected Type I error rates for S - chi(2) and chi(2*). Adjusted chi(2)/dfs resulted in large Type I error rates when used with cross validation and very low Type I error rates when used without cross validation. chi(2*) and adjusted chi(2)/dfs without cross validation were the most powerful overall.