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NAEP Analysis and Scaling → Estimation of NAEP Score Scales → Assumptions of the Item Scaling Models

Assumptions of the Item Scaling Models

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Local Independence

Unidimensionality

Context Effects

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When using the two-parameter logistic, three-parameter logistic, and generalized partial credit item scaling models, NAEP makes assumptions about the dimensionality of the construct being measured and local independence of the student response data. The scaling areas in NAEP are determined a priori by grouping items into content areas for which overall performance is deemed to be of interest, as defined by the NAEP frameworks. Local independence refers to the assumption that responses of an individual to a set of items depend only on the individual’s underlying knowledge in the scaling area. If there are context effects for an item, the responses to that item depend on the location of the item in the assessment booklet.


Last updated 14 July 2008 (DB)

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