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NAEP Analysis and Scaling → Estimation of NAEP Score Scales → Checks for Violations of Assumptions → Comparisons of Empirical and Theoretical Item Response Functions → Items Showing Good Item Fit

NAEP Technical DocumentationItems Showing Good Item Fit

			Dichotomous Item With Data for One Assessment Year Polytomous Item With Data for One Assessment Year Dichotomous Item With Data for Two Assessment Years Polytomous Item With Data for Two Assessment Years

Items with student responses that can be well described by Item Response Theory (IRT) models have empirical and theoretical item response functions (IRFs) that are close to one another. Loosely speaking, the proportions of students at each score level who actually do give good responses to an item should be close to the theoretical proportions that are estimated using the IRT models. Examples of dichotomous and polytomous items with data from one or two assessment years provide guidelines for the recognition of good fit. For these examples the symbols representing the empirical proportions overlay the theoretical probabilities that are represented by the continuous curves.

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