NAEP Technical DocumentationStratification of Private Schools for the 2008 Long-Term Trend (LTT) Assessment

Separate implicit stratification schemes were used to sort schools in certainty primary sampling units (PSUs) and noncertainty PSUs. In all cases, the implicit stratification was achieved via a "serpentine sort."

For certainty PSUs, the schools were hierarchically sorted by

Census region,
private school type (Roman Catholic, Lutheran, Conservative Christian, Other religious, Nonsectarian, and Affiliation Unknown),
race/ethnicity strata, and
estimated number of age eligible students.

If there were fewer than two expected sampled schools for a particular school type cell (in other words, the aggregated probabilities of selection across the schools within the cells are less than or equal to 2), the cell was collapsed with a neighboring school type cell. If the expected sampled schools equaled or exceeded four, the race/ethnicity stratum is defined based on the summation of school percentages of Black, Hispanic, and American Indian/Alaska Native students. The race/ethnicity stratum was defined so that there was at least two expected sampled schools for each school type stratum (nested within the Census region). If the school type stratum had an expected sample size less than four, no race/ethnicity strata were generated, and the final sort variable was the summation of school percentages of Black, Hispanic, and American Indian/Alaska Native students rather than estimated age eligible students.

Schools in noncertainty PSUs were hierarchically sorted by

PSU stratum,
private school type,
percent race/ethnicity.

Race/ethnicity percentages for each school are the summation of the school percentages of Black, Hispanic, and American Indian/Alaska Native students.

Last updated 15 March 2011 (GF)

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