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NAEP Technical Documentation Formation of Primary Sampling Units (PSUs) for the 2016 Assessment: Non-Metro Areas
Primary sampling units (PSUs) for NAEP are classified as either metro area or non-metro area. Non-metro area PSUs are PSUs that are made up of counties that are not part of any metropolitan statistical areas1.
An algorithm was used to define a preliminary set of non-metro area PSUs satisfying specific design constraints. The algorithm attempted to form PSUs that were geographically compact, of a minimum population size (15,000 youths in the Northeast and South census regions, and 10,000 youths in the Midwest and West census regions) and that also did not cross state boundaries. The input set consisted of all non-metro area counties. The county which had the largest maximum point-to-point distance was addressed first. It was grouped with adjacent non-metro area counties until the minimum PSU size was met. The algorithm was then run on the remaining non-metro area counties not yet assigned to a PSU to combine the county with the largest maximum point-to-point distance among the remaining counties with its adjacent non-metro area counties until the minumum PSU size was met. This process was repeated until all counties were grouped into PSUs.
When the algorithm was unable to create PSUs that conformed to the specific design constraints, manual adjustments were made. The end result of this procedure was that all non-metro area PSUs were contained within state boundaries, but in some cases the PSU size fell slightly below the pre-specified minimum.
In total, there were 629 non-metro area PSUs covering a total of 2,043 counties, all of which constitute the non-metro area PSU sampling frame. The table below presents the number of PSUs, the number of counties represented, and the estimated number of youths (total and mean per PSU) in the non-metro area PSU sampling frame by census region. The estimated number of youths (persons aged 0 to 17) for each county comes from the 2013 U.S. Census Bureau population estimates.
| Census region | PSUs | Counties | Youths | Mean number of youths per PSU |
|---|---|---|---|---|
| SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2016 Assessment. | ||||
| Total | 629 | 2,043 | 11,303,722 | 17,971 |
| Northeast | 48 | 94 | 1,077,588 | 22,450 |
| Midwest | 228 | 762 | 3,465,371 | 15,199 |
| South | 250 | 871 | 5,099,762 | 20,399 |
| West | 103 | 316 | 1,661,001 | 16,126 |
1 Based on the 2009 metro area definitions, the most recent available metro area definitions at the time of PSU construction, from the U.S. Office of Management and Budget (OMB Bulletin No. 10-02).
Last updated 10 February 2022 (SK)