NAEP Technical DocumentationStratification Variables

The first level of stratification for the NAEP 2005 national science sample, within each grade, was study type. Study type differed by jurisdiction, and was defined as follows:

Study type 1: Supplemental national science operational assessment, no science bridge. This stratum includes Alaska only.
Study type 2: Supplemental national science bridge and pilot studies, no national science operational assessment. This stratum includes all jurisdictions which agreed to do the national science operational assessment as part of NAEP State, and which were not excluded from the science bridge study.
Study type 3: Supplemental national science operational, science bridge, and pilot studies. This stratum includes jurisdictions which refused to do the state science operational assessment and which were not excluded from the science bridge or pilot studies.

The next level of stratification following study type utilized Census division. Since Alaska is the sole jurisdiction assigned to the first study type stratum, there was only one Census division (the Pacific division). In the second study type stratum (containing the majority of the jurisdictions), all nine Census divisions were strata. In the third study type stratum, which contained a limited set of jurisdictions, the geographic stratification was collapsed to two strata: the Census Northeast Region and the remainder of the country (Midwest, South, West Regions).

The next level of stratification was the urbanization classification, drawn from the CCD and defined as follows:

Large Central 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.
Mid-size Central City: A principal city of a Metropolitan CBSA, with the city having a population less than 250,000.
Urban Fringe of Large City: Any incorporated place, Census designated place, or non-place territory within a CBSA of a Large City and defined as urban by the Census Bureau.
Urban Fringe of 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.
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.
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.
Rural, outside CBSA: Any incorporated place, Census designated place, or non-place territory within a Metropolitan CBSA or within a Micropolitan CBSA and defined as rural by the Census Bureau.
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.
Outside of United States (international Defense Department schools and Puerto Rico).

Urban city status cells within a study type/geography stratum which contained a too-small enrollment were collapsed. The criterion for adequacy was that the cell had to yield a minimum of six expected hits. Categories 1 through 4 of the urbanization variable were nearly always kept separate from Categories 5 through 8, even if the condition of fewer than six expected hits was violated. The only exception was Alaska, the only jurisdiction in the supplemental national science-operational-only stratum. All urban city categories were collapsed into a single stratum, and this single stratum still had fewer than six expected hits but was not collapsed further.

Last updated 14 July 2009 (JL)

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