NAEP Technical Documentation2012 Private School Long-Term Trend (LTT) Assessment
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The NAEP 2012 long-term trend (LTT) assessment sample design yielded a nationally representative sample of private school students in each age group (9, 13, and 17) through a three-stage approach: selection of primary sampling units (PSUs), selection of schools within strata, and selection of students within schools. The sample of schools was selected with probability proportional to a measure of size based on the estimated age-specific enrollment in the schools.
The 2012 sampling plan was designed to assess 1,700 students for each of the LTT private school age-specific samples. These students were allocated among four different tests. The operational tests were in reading and mathematics and pilot tests were also conducted in reading and mathematics. Target sample sizes were adjusted to reflect expected private school and student response and eligibility.
The private school samples were drawn from a sampling frame that only included the sampled LTT primary sampling units (PSUs). Schools on the sampling frame were explicitly stratified prior to sampling by private school affiliation (Catholic, non-Catholic private, and unaffiliated). Within affiliation type, schools were implicitly stratified by PSU type (certainty/noncertainty). In certainty PSUs, further stratification was by census region, urbanization classification (based on urban-centric locale), and estimated age-specific enrollment. In noncertainty PSUs, additional stratification was by PSU stratum, urbanization classification (based on urban-centric locale), and estimated age-specific enrollment.
From the stratified frame of private schools, systematic random samples of schools in each age group (9, 13, and 17) were drawn with probability proportional to a measure of size based on the estimated age-specific enrollment of the school. The number of age-eligible students was estimated by applying population-level percentages of age-eligible students within each grade to estimated grade enrollments for each grade, and aggregating to an age-eligible total for the school.
Each selected school was asked to provide a roster of all of its students who were age-eligible. A fixed sample of 64 students was selected from these rosters, with the exception of smaller schools with total age-eligible counts less than the sample size. The combination of using the number of age-eligible students as a measure of size and a fixed sample size of students is intended to give a self-weighting sample (each student has an equal probability of selection). In practice, differences between the estimated age-eligible enrollment for the school and the actual size of the finalized roster introduce slightly differing student probabilities across schools.
Last updated 27 July 2012 (SS)