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 Conditioning Model, by Grade and Scale, Reading Vocabulary National Assessment: 2009

NAEP Technical DocumentationProportion of scale score variance accounted for by the conditioning model, by grade and scale, reading vocabulary national assessment: 2009

Grade	Number of initial conditioning contrasts2	Number of principal components2	Proportion1 of scale score variance
			OneScale3
1 (Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. 2 Excluding the constant term. 3 Single overall scale. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Reading Vocabulary Assessment.
4	1120	147	0.31
8	1125	141	0.35
12	1125	49	0.27

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