NAEP Technical DocumentationStratification of Public Schools for the 2014 Social Studies Assessment

For the public school sampling frame file, separate implicit stratification schemes were used to sort schools into certainty primary sampling units (PSUs) and noncertainty PSUs. The implicit stratification was achieved via a "serpentine sort."

For certainty PSUs, the schools were hierarchically sorted by

• census region,
• urbanization classification (four categories based on urban-centric locale),
• race/ethnicity strata, and
• estimated grade enrollment.

If there were less than six expected sampled schools for a particular urbanization classification cell (nested within the census region), the cell was collapsed with a neighboring urbanization classification cell. If the expected sampled schools exceeded 12, then the race/ethnicity strata were defined based on the percentages of Black, Hispanic, and American Indian/Alaska Native students. The strata were defined so that there were at least six expected sampled schools for each race/ethnicity stratum. If the urbanization classification stratum had an expected sample size less than 12, no race/ethnicity strata were generated, and the final sort variable was percentages of Black, Hispanic, and American Indian/Alaska Native students rather than estimated grade enrollment.

Schools in noncertainty PSUs were hierarchically sorted by

• PSU stratum,
• urbanization classification (four categories based on urban-centric locale), and
• percent race/ethnicity (Black, Hispanic, and American Indian/Alaska Native students).

The collapsing of cells within the noncertainty PSUs was implemented in a fashion similar to that described for certainty PSUs.

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