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, Age 13 Reading Long-Term Trend Assessment: 2012

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, age 13 reading long-term trend assessment: 2012

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. 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), 2012 Reading Long-Term Trend Assessment.
All contrasts	502	0.90	0.66	0.99	3	43	140	203	113
Student questionnaire	75	0.90	0.66	0.99	1	9	19	20	26
Major reporting variables	83	0.91	0.74	0.99	0	4	24	23	32
Interactions between reporting variables	310	0.90	0.68	0.98	2	26	86	150	46
SD/ELL questionnaire	34	0.89	0.77	0.98	0	4	11	10	9

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