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, Grade 8 Reading Combined National and State Main Assessment: 2009

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: 2009

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	0.95 - 1.00
1(Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. NOTE: NIES = National Indian Education Study; 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), 2009 Reading Assessment.
All contrasts	2,359	0.90	0.61	1.00	16	100	999	668	576
Student questionnaire	206	0.90	0.61	0.99	3	19	48	82	54
Major reporting variables	111	0.93	0.79	1.00	0	1	28	36	46
Interaction between reporting variables	575	0.91	0.63	0.99	12	22	134	188	219
Teacher questionnaire	333	0.91	0.73	0.99	0	11	95	121	106
School questionnaire	750	0.89	0.77	0.99	0	8	468	182	92
NIES questionnaire	341	0.87	0.66	0.99	1	35	214	52	39
SD/ELL questionnaire	43	0.91	0.78	0.99	0	4	12	7	20

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