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Characteristics of Public School Districts in the United States:
NCES 2009-320
June 2009

Appendix B. Methodology and Technical Notes—Variance Estimation

In surveys with complex sample designs, such as SASS, direct estimates of sampling errors that assume a simple random sample typically underestimate the variability in the estimates. The SASS sample design and estimation include procedures that deviate from the assumption of simple random sampling, such as stratifying the school sample, oversampling new teachers, and sampling with differential probabilities.

One method of calculating sampling errors of complex sample designs is replication. Replication methods involve constructing a number of subsamples (i.e., replicates) from the full sample and computing the statistic of interest for each replicate. The mean square error of the replicate estimates around the full sample estimate provides an estimate of the variance of the statistic. Each SASS data file includes a set of 88 replicate weights designed to produce variance estimates. The set of replicate weights for each file should be applied to the respondents in that file. The replicate weights for SASS respondents are DREPWT1–DREPWT88 for districts, AREPWT1–AREPWT88 for principals, SREPWT1–SREPWT88 for schools, TREPWT1–TREPWT88 for teachers, and MREPWT1–MREPWT88 for library media centers.

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