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NAEP Technical DocumentationTrimming of School Base Weights for the 2008 Arts Assessment
Large school weights can occur for schools selected through the new schools sampling procedure and for private schools. In 2008, no new public schools were selected for the arts assessment. For this reason, only private schools were eligible for assessment of extreme school base weights. Private schools eligible for weight trimming were Private School Universe Survey (PSS) nonrespondents who were found subsequently to have larger enrollments than assumed at the time of sampling. (Note that, prior to sampling, the same nominal value was assigned to all schools with unknown enrollment.)
To detect extremely large weights among private schools, a comparison was made between a school's school base weight and its ideal weight (i.e., the weight it would have had had it been on the list frame portion of the PSS universe file at the time of NAEP school sampling, with an accurate enrollment figure and a known affiliation). If the school base weight was more than three times the ideal weight, a trimming factor was calculated for the school that scaled the base weight back to three times the ideal weight. The calculation of the school-level trimming factor for a new school s is expressed in the following formula:
where
EXP_WTs is the ideal base weight the school would have received if it had been on the list frame portion of the PSS universe file at the time of NAEP school sampling with an accurate enrollment and known affiliation, and
SCH_BWTs is the actual school base weight the school received as a sampled private school.
Less than five private schools had their weights trimmed.
Last updated 12 August 2010 (DH)
