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HomeTDWNAEP Analysis and ScalingEstimation of Population and Student Group DistributionsExamining the Population-Structure Models Used in NAEPProportion of Scale Score Variance Accounted for by the Population-Structure ModelProportion of Scale Score Variance Accounted for by the Population-Structure Model, Civics National Main Assessment, by Grade: 2006

NAEP Technical DocumentationProportion of scale score variance accounted for by the population-structure model, civics national main 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
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 Civics Assessment.
4	2370	339	1.00
8	2620	343	1.00
12	2591	314	1.00

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