NAEP Technical Documentation 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 Assessment, by Type of Contrast: 2015

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 assessment, by type of contrast: 2015

Type of contrast	Number of contrasts	Mean	Minimum	Maximum	Number of contrasts by proportion of variance explained1
					.00 - .70	.70 - .80	.80 - .90	.90 - .95	.95 - 1.00
All contrasts	2100	.90	.66	1.00	9	78	923	666	424
Student questionnaire	203	.91	.69	.99	3	15	50	80	55
Major reporting variables	127	.93	.69	1.00	1	2	33	42	49
Interactions between reporting variables	380	.90	.66	.98	4	16	110	192	58
Teacher questionnaire	302	.92	.74	.99	0	7	92	96	107
School questionnaire	771	.90	.79	.99	0	4	438	208	121
NIES questionnaire	282	.86	.69	.99	1	33	187	43	18
SD/EL questionnaire	35	.91	.79	1.00	0	1	13	5	16
1 (Total Variance – Residual Variance) / Total Variance, where Total Variance consists of sampling, measurement, and other sources of error. NOTE: NIES = National Indian Education Study. SD/EL = Students with disabilities/English learners. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2015 Reading Assessment.

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