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

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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—X², X2, and adjusted X² degrees of freedom ratios (X²/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—X² and X2. Adjusted X²/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. X2 and adjusted X²/dfs without cross validation were the most powerful overall.



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