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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, Science Combined National and State Main Assessment, by Subscale and Grade: 2005

NAEP Technical DocumentationProportion of scale score variance accounted for by the population-structure models, science combined national and state main assessment, by subscale and grade: 2005

Grade	Number of initial conditioning contrasts2	Number of principal components2	Proportion1 of scale score variance
			Physical	Earth	Life
4	3,240	549	0.52	0.55	0.52
8	3,220	441	0.55	0.52	0.55
12	2,451	368	0.65	0.62	0.65
1 (Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. 2 Excluding the constant term. NOTE: There were no state assessments for grade 12 in 2005. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2005 Science Assessment.

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