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NAEP Sample Design → NAEP 2005 Sample Design → National Assessment Sample Design → Private School National Assessment → Stratification of Schools in the 2005 National Private School Assessments

NAEP Technical DocumentationStratification of Schools in the 2005 National Private School Assessments

The stratification of the schools involved four dimensions. Explicit stratification for the NAEP 2005 private school sample was by private school type: Roman Catholic, Lutheran, Conservative Christian, Other Private, and Unknown Affiliation. Private school affiliation was unknown for nonrespondents to the NCES Private School Survey (PSS).

Within each explicit stratum, the private schools were hierarchically sorted by census division, urbanicity status, race/ethnicity status, and estimated grade enrollment. The implicit stratification in this four-fold hierarchical stratification was achieved via a "serpentine sort".

Census division was used as the first level of implicit stratification for the NAEP 2005 private school sample. For the larger private school type strata (e.g. Roman Catholic schools), all nine Census divisions were used as strata. For the smaller private school type strata, the Census divisions were collapsed.

Census division cells within a private school type stratum which did not meet the minimum of six expected hits were collapsed. This occurred especially for the Lutheran and Affiliation Unknown strata and, to a limited degree, in the other strata as well. Census division was collapsed within Census region in general and further collapsed as needed. The following table documents the relationship between Census division (CENSDIV) and Census region (CENSREGN) and identifies the numeric codes associated with each.

Census division (CENSDIV) and Census region (CENSREGN), national main assessment, by numeric code: 200

CENSDIV	Division	CENSREGN	Region
1	New England	1	Northeast
2	Middle Atlantic	1	Northeast
3	East North Central	2	Midwest
4	West North Central	2	Midwest
5	South Atlantic	3	South
6	East South Central	3	South
7	West South Central	3	South
8	Mountain	4	West
9	Pacific	4	West
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2005.

The next level of stratification was an urbanization classification, as defined by the PSS:

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.

Urbanicity status cells within a geography stratum which did not meet the minimum of six expected hits were collapsed, as were the Census Division strata. The criterion for adequacy was that the cell had to correspond to a minimum of six expected hits. The urbanization variable was equal to the original type of location if no collapsing was necessary to cover an inadequate original cell. For example, type of location categories 1 and 2 are collapsed if either cell has less than six expected hits. That is, a single category would be created by combining Large City with Mid-size City. If these collapsed cells were still inadequate, they were further collapsed with the two types of Urban Fringe cells to form a single cell made up of large and mid-size cities and the urban fringes of large and mid-size cities. The urbanization variable was equal to the cell value of the final level of collapsing. Prior experience with this type of stratification showed that the greatest efficiency of stratification resulted when cities and urban fringe areas were kept separate from towns and rural areas, even if the six expected hits condition was violated. Finally, the type of location missing category (Category 9) was always kept as a separate stratum.

The last stage of stratification was a division of the geographic/urbanicity strata into race/ethnicity strata, if the expected number of hits was large enough (i.e., at least equal to 12). This was done by deciding first on the number of race/ethnicity strata and then dividing the geography/urbanicity stratum into this many race/ethnicity strata by using a sorted list based on percentage of students who are Black, Hispanic, or American Indian and then divided into three sets using that ordering (lowest percentage, middle percentage, highest percentage), with roughly equal expected hits for each set.  The race/ethnic groups included are those that have traditionally performed substantially lower on NAEP assessments than white students.

Schools were sorted within stratification cells by estimated grade enrollment.

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