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 Geography National Assessment: 2010

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 8 geography national assessment: 2010

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), 2010 Geography Assessment.
All contrasts	1424	0.90	0.64	0.99	9	51	621	456	287
Student questionnaire	221	0.89	0.64	0.99	5	17	78	81	40
Major reporting variables	63	0.92	0.76	0.99	0	2	25	13	23
Interactions between reporting variables	466	0.91	0.68	0.99	4	29	135	146	152
Teacher questionnaire	380	0.89	0.79	0.98	0	2	232	117	29
School questionnaire	258	0.91	0.84	0.99	0	0	134	88	36
SD/ELL questionnaire	36	0.89	0.80	0.98	0	1	17	11	7

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