​​​​NAEP Technical DocumentationEstimation of NAEP Score Scales

			NAEP Scales Item Scaling Models Estimation of IRT Item Parameters Treatment of Missing Responses in NAEP Assumptions of the Item Scaling Models Checks for Violations of Assumptions Treatment of Items to Avoid Violations of Assumptions NAEP Assessment IRT Parameters ​

NAEP score scales summarize statistics describing scale scores for groups of students for the collection of items representing the content specified in the NAEP frameworks. For each subject area, the framework determines the number of Item Response Theory (IRT) scales.

IRT models are used to describe the relationships between the item responses provided by students and the underlying score scales. IRT provides a common scale on which the performance of students receiving different blocks of items can be placed. For each item, item parameters that are used in the models are estimated from student response data. Different IRT models with different types of item parameters are used to describe multiple-choice items, constructed-response items that are scored right or wrong, and constructed-response items that have more than two categories. However, all types of items contribute to NAEP score scales. Evaluation of model fit is done during the item parameter estimation procedure.

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