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 Reading National Main Assessment: 2009

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 12 reading national main assessment: 2009

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	0.95 - 1.00
1(Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. NOTE: SD/ELL = Students with disabilities/English language learners. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Reading Assessment.
All contrasts	1,521	0.90	0.58	0.99	19	48	655	461	338
Student questionnaire	218	0.88	0.61	0.99	5	15	92	77	29
Major reporting variables	71	0.92	0.79	0.99	0	1	27	15	28
Interaction between reporting variables	518	0.91	0.58	0.99	14	27	111	156	210
School questionnaire	678	0.89	0.81	0.99	0	0	418	201	59
SD/ELL questionnaire	36	0.90	0.71	0.99	0	5	7	12	12

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