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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 Model → Proportion of Scale Score Variance Accounted for by the Population-Structure Model, Writing Combined National and State Main Assessment, By Scale and Grade: 2007

NAEP Technical DocumentationProportion of scale score variance accounted for by the population-structure model, writing combined national and state main assessment, by scale and grade: 2007

Grade	Number of initial group-defining contrasts2	Number of principal components2	Proportion1of scale score variance for by the population-structure model
				1 (Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. 2 Excluding the constant term. NOTE: The writing assessment had a single overall scale. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2007 Writing Assessment.
8	4172	646	1.00
12	2529	321	1.00

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