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NAEP Sample Design → NAEP 2005 Sample Design → National Assessment Sample Design → Twelfth-Grade Public School National Assessment → Stratification of Schools in the 2005 National Twelfth-Grade Public School Assessments

NAEP Technical DocumentationStratification of Schools in the 2005 National Twelfth-Grade Public School Assessments

Implicit stratification of twelfth-grade public schools involved four dimensions:

• Census division,
• urbanization classification,
•  race/ethnicity status, and
• estimated grade enrollment.

Any urbanization classification category with an expected sample size fewer than four schools was combined with another type of location category within the same Census division. In all cases, the category "large town" contained too few schools and was combined with the category "small town." After combining, there were 57 final Census division-urbanicity strata, ordered by urbanization classification within Census division.

These 57 cells were then divided into subclasses by race/ethnicity status (less than 15% black and Hispanic students or more than 15% black and Hispanic students). In some of these Census division-urbanicity cells, only one race/ethnicity status was represented. In other cases, the expected sample size within the race/ethnicity status cell was very large. The low-race/ethnicity cells with particularly large expected sample sizes were divided by state or contiguous groups of states into two or three cells.

The final aspect of the implicit stratification was a sorting within the final cells by estimated grade enrollment.

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