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 9 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 9 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	431	0.90	0.67	0.99	5	27	151	141	107
Student questionnaire	63	0.90	0.67	0.99	3	8	10	17	25
Major reporting variables	84	0.92	0.70	0.99	0	5	17	23	39
Interactions between reporting variables	246	0.89	0.69	0.97	2	13	107	92	32
SD/ELL questionnaire	38	0.90	0.78	0.98	0	1	17	9	11

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