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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, U.S. History National Assessment, by Grade: 2006

NAEP Technical DocumentationProportion of scale score variance accounted for by the population-structure model, U.S history national assessment, by scale and grade: 2006

Grade	Number of initial group-defining contrasts2	Number of principal components2	Proportion1 of scale score variance accounted for by the population-structure model
			Democracy	Cultures	Technology	World role
1 (Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. 2 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), 2006 U.S. History Assessment.
4	2376	327	0.60	0.61	0.65	0.64
8	2632	350	0.65	0.64	0.64	0.67
12	2608	320	0.63	0.64	0.63	0.62

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