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NAEP Assessment Sample Design → NAEP 2007 Sample Design → Sample Design for the 2007 National Assessment → 2007 Twelfth-Grade Public School National Sample → Stratification of Schools for the 2007 Twelfth-Grade Public School National Assessment

NAEP Technical DocumentationStratification of Schools for the 2007 Twelfth-Grade Public School National Assessment

There are two types of stratification, explicit and implicit. Explicit stratification was not used for the twelfth-grade public school sample. Implicit stratification of twelfth-grade public schools involved four dimensions:

• Census division,
• urbanization classification,
• Black/Hispanic status, and
• estimated grade enrollment.

Any urbanization classification category with an expected sample size of fewer than four schools was combined with another type of location category within the same Census division. The urbanization classification is as defined by the Common Core of Data (CCD):

1. Large City: A principal city of a Metropolitan Core Based Statistical Area (CBSA), with the city having a population greater than or equal to 250,000.

2. Mid-size City: A principal city of a Metropolitan CBSA, with the city having a population less than 250,000.

3. Urban Fringe of a Large City: Any incorporated place, Census-designated place, or non-place territory within a Metropolitan CBSA of a Large City and defined as urban by the Census Bureau.

4. Urban Fringe of a Mid-size City: Any incorporated place, Census-designated place, or non-place territory within a CBSA of a Mid-size City and defined as urban by the Census Bureau.

5. Large Town: An incorporated place or Census-designated place with a population greater than or equal to 25,000 and located outside a Metropolitan CBSA or inside a Micropolitan CBSA.

6. Small Town: An incorporated place or Census-designated place with population less than 25,000 and greater than or equal to 2,500 and located outside a Metropolitan CBSA or inside a Micropolitan CBSA.

7. Rural, outside CBSA: Any incorporated place, Census-designated place, or non-place territory not within a Metropolitan CBSA or within a Micropolitan CBSA and defined as rural by the Census Bureau.

8. Rural, inside CBSA: Any incorporated place, Census-designated place, or non-place territory within a Metropolitan CBSA and defined as rural by the Census Bureau.

9. Outside of the United States: Department of Defense (DoD) International school or Puerto Rico.

These Census division-urbanicity cells were then divided into subclasses by Black/Hispanic status (less than 15 percent Black and Hispanic students or more than 15 percent Black and Hispanic students). In some of these Census division-urbanicity cells, only one Black/Hispanic status was represented. In other cases, the expected sample size within the Black/Hispanic status cell was very large. The low Black/Hispanic 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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