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Age | Number of initial conditioning contrasts1 | Number of principal components1 | Proportion2 of scale score variance |
---|---|---|---|
9 | 1,504 | 130 | 0.35 |
13 | 1,761 | 157 | 0.43 |
17 | 1,768 | 156 | 0.42 |
1 Excluding the constant term. 2(Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2004 Mathematics Long-Term Trend Assessment. |