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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 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, Grade 12 U.S. History National Main Assessment: 2006

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 12 U.S. history national main assessment: 2006

Type of contrast	Number of contrasts	Mean	Minimum	Maximum	Number of contrasts by proportion1 of variance explained
					0.00 - 0.70	0.70 - 0.80	0.80 - 0.90	0.90 - 0.95	0.95 - 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), 2006 U.S. History Assessment.
All contrasts	972	0.90	0.61	0.99	11	45	395	294	227
Student questionnaire	182	0.89	0.61	0.99	5	19	59	58	41
Major reporting variables	58	0.92	0.80	0.99	0	2	25	5	26
Interactions between reporting variables	434	0.92	0.67	0.98	6	22	100	152	154
School questionnaire	298	0.88	0.79	0.96	0	2	211	79	6

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