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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 12 Writing National Main Assessment: 2002

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 12 writing national main assessment: 2002

Type of contrast	Number of contrasts	Mean	Minimum	Maximum	Number of contrasts by proportion of variance explained
					0.00 - 0.70	0.70 - 0.80	0.80 - 0.90	0.90 - 0.95	0.95 - 1.00
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2002 Writing Assessment.
All contrasts	860	0.90	0.69	0.99	1	32	385	259	183
Student questionnaire	213	0.90	0.69	0.98	1	10	89	66	47
Major reporting variables	52	0.91	0.81	0.99	0	0	25	5	22
Interactions between reporting variables	243	0.90	0.71	0.99	0	22	89	79	53
School questionnaire	352	0.90	0.80	0.99	0	0	182	109	61

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