NAEP Technical DocumentationSelection of Primary Sampling Units (PSUs) for the 2018 Assessment

			PSU Generation: Metropolitan Statistical Areas PSU Generation: Certainty PSUs PSU Generation: Non-Metropolitan Statistical Areas PSU Frame Stratification Final PSU Samples

The first stage of sampling for the 2018 assessment was the selection of primary sampling units (PSUs). A PSU is a geographic area comprising an individual county or a group of contiguous counties. Three sets of sample PSUs were selected for the 2018 assessments: one for the social sciences assessments, one for the technology and engineering literacy (TEL) assessment, and one for the pilot and special studies assessments. For social sciences, 105 PSUs were selected. For TEL and pilot/special studies, two sets of 67 PSUs were selected.

The PSU samples were drawn using a stratified sample design with one PSU selected per stratum or stratum pair with probability proportional to population size. The size measure used for PSU sampling was persons 17 years of age and younger from 2015 U.S. Census Bureau population estimates.

The PSU sampling frame was constructed by partitioning all counties in the entire United States (the 50 states and the District of Columbia) into 1,001 non-overlapping PSUs as follows:

• Each metropolitan statistical area (metro area) was considered a separate PSU, unless it crossed census region boundaries. When this happened, the part within each region was made a separate PSU; and

• Non-metro area PSUs were constructed from contiguous non-metro area counties within the same state that had minimum populations of 15,000 youths in the Northeast and South census regions and 10,000 youths in the Midwest and West census regions.

Measures of size for constructing the PSUs were based on youth population data obtained from the 2010 Decennial Census summary files.

For all three PSU samples, 29 PSUs on the PSU sampling frame were included in the sample with certainty (selected with a probability of 1). The inclusion of these PSUs in the sample with certainty provided the approximate optimum, cost-efficient sample of schools and students when samples were drawn within them at the required national sampling rate.

The remaining PSUs were grouped into noncertainty PSU sampling strata within eight primary strata, which were defined by census region and metropolitan status. The stratification of PSUs within the eight primary strata was based on characteristics shown to be highly correlated with student performance such as minority status, income, education, renter status, and percentage of female-headed households. These data were obtained at the county level from the 2006–10 American Community Survey (ACS) and then aggregated to the PSU level. Seventy-six noncertainty PSU strata were formed. These PSU strata were then paired to form 38 stratum pairs.

Printer-friendly Version