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NAEP Sample Design → NAEP 2004 Long-Term Trend Sample Design → Sampling of Schools and Students → Long-Term Trend School Stratification → Long-Term Trend Private School Stratification

NAEP Technical DocumentationLong-Term Trend Private School Stratification

The primary stratifiers for private schools were NAEP region for the certainty PSU schools and PSU stratum for the noncertainty PSU schools. Within these strata, school type was the next strata categorizer:

• Conservative Christian,
• Lutheran,
• other private nonreligious,
• other religious, and
• Roman Catholic. 

If a school-type stratum had an aggregate measure of size corresponding to less than 2 sampled schools (i.e., the expected sample size from the stratum is less than 2), it was collapsed with the neighboring school-type stratum. The bullets below present the collapsing that was done for the certainty PSU stratum, for each NAEP region stratum.

• NAEP Region 1 (Northeast): Catholic and Lutheran levels collapsed.
• NAEP Region 2 (Southeast): Catholic and Lutheran levels collapsed.
• NAEP Region 3 (Central): no collapsing.
• NAEP Region 4 (West): no collapsing.

No collapsing of school-type strata was done within the noncertainty PSU strata.

Within the school-type strata, race/ethnicity percentages served as the next implicit stratifier (defined as the summation of percent Black, percent Hispanic, and percent Native American). For noncertainty PSUs, this was the final level of implicit stratification: race/ethnicity percentage was the final sort variable in the serpentine sort order that determined the frame order. Also for certainty PSUs, if the school-type stratum had an aggregate measure of size less than 4.0 (i.e., the expected sample size from the stratum is less than 4.0), the last stage in the serpentine sort ordering was an ordering by race/ethnicity percentage.

For certainty PSU school-type strata with a larger aggregate measure of size (4.0 or greater), race/ethnicity strata were generated, with roughly one race/ethnicity stratum per aggregate measure of size 2.0. For example, a school-type stratum with aggregate measure of size of 4.0 up to 6.0 would have two race/ethnicity strata, a school-type stratum with aggregate measure of size of 6.0 to 8.0 sampled schools would have three race/ethnicity strata, etc. If race/ethnicity strata were generated, then grade enrollment was used as a final sort within each race/ethnicity stratum. The idea was to use both race/ethnicity percentage and grade enrollment as implicit strata if there were enough schools, and otherwise use only race/ethnicity percentage. Of the 17 NAEP-school-type strata defined for the certainty PSUs, 8 had aggregate measures of size less than 4.0 (and had race/ethnicity percentage as the final sort variables), and 9 had aggregate measures of size greater than 4.0 (and had race/ethnicity strata with grade enrollment percentage as the final sort variable).

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