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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 Variance Accounted for by the Principal Components Used in NAEP Population-Structure Models → Proportion of Variance of the Group-Defining Contrasts Accounted for by the Principal Components Used in the Population-Structure Model, Age 17 Reading Long-Term Trend Assessment: 2008

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, age 17 reading long-term trend assessment: 2008
Type of contrast Number of contrasts Mean Minimum Maximum Number of contrasts by proportion1 of variance explained
0.00 - 0.70 0.71 - 0.80 0.81 - 0.90 0.91 - 0.95 0.96- 1.00
1(Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance.
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2008 Reading Long-Term Trend Assessment.
All contrasts 636 0.90 0.56 0.99 21 50 164 210 191
Student questionnaire 85 0.89 0.58 0.99 3 9 27 25 21
Major reporting variables 58 0.90 0.65 0.99 3 6 14 14 21
Interactions between reporting variables 455 0.91 0.56 0.98 15 30 107 161 142
SD/ELL questionnaire 38 0.88 0.76 0.98 0 5 16 10 7
Last updated 14 December 2011 (GF)
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