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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 of the Group-Defining Contrasts Accounted for by the Principal Components Used in NAEP Student Group Distribution Models → Proportion of Variance of the Group-Defining Contrasts Accounted for by the Principal Components Used in the Population-Structure Model, Grade 8 Reading Combined National and State Main Assessment: 2005

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 8 reading combined national and state main assessment: 2005

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), 2005 Reading Assessment.
All contrasts	1,352	0.90	0.55	0.99	26	106	423	352	445
Student questionnaire	203	0.89	0.55	0.99	2	22	71	64	44
Major reporting variables	98	0.93	0.74	0.99	0	3	24	21	50
Interactions between reporting variables	625	0.91	0.59	0.99	18	40	169	144	254
Teacher questionnaire	237	0.88	0.62	0.99	4	21	106	51	55
School questionnaire	189	0.89	0.65	0.98	2	20	53	72	42

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