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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 Civics 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 civics 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 Civics Assessment.
All contrasts	1008	0.90	0.66	0.99	8	50	406	322	222
Student questionnaire	171	0.87	0.68	0.99	4	31	64	53	19
Major reporting variables	57	0.93	0.81	0.99	0	0	23	8	26
Interactions between reporting variables	484	0.92	0.66	0.99	4	19	116	170	175
School questionnaire	296	0.89	0.80	0.96	0	0	203	91	2

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