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NAEP Sample Design → NAEP 2005 Sample Design → National Assessment Sample Design → Fourth- and Eighth-Grade Public School Science Assessment and Bridge Study → Stratification of Schools in the 2005 National Science Assessments

NAEP Technical DocumentationStratification of Schools in the 2005 National Science Assessments

			Stratification Variables

The stratification of the fourth- and eighth-grade national science samples involved the four elements shown below. The only explicit stratification was by grade. The public schools in each grade were hierarchically stratified as follows:

1. study type (jurisdictions assigned only a supplemental national science operational assessment [Alaska], jurisdictions needing science bridge and pilot studies only, jurisdictions needing all three);
2. Census division;
3. urbanicity status; and
4. estimated grade enrollment.

The implicit stratification in this four-fold hierarchical stratification was achieved via a "serpentine sort".

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