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NAEP Analysis and Scaling → Estimation of Population and Student Group Distributions → Examining the Population-Structure Models Used in NAEP → Proportion of Scale Score Variance Accounted for by the Population-Structure Models → Proportion of Scale Score Variance Accounted for by the Population-Structure Models, Reading Combined National and State Assessment, by Grade: 2003

NAEP Technical DocumentationProportion of scale score variance accounted for by the population-structure models, by grade, reading combined national and state assessment: 2003

Grade	Number of initial group-defining contrasts1	Number of principal components1	Proportion of scale score variance
			Reading for literary experience	Reading to gain information	Reading to perform a task
4	2,640	495	0.45	0.48	†
8	2,442	478	0.46	0.51	0.56
† The NAEP reading assessment does not assess the "reading to perform a task" scale at grade 4. 1 Excluding the constant term. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2003 Reading Assessment.

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