NAEP TechnicaL Documentation Primary Sampling Unit (PSU) Generation: Metropolitan Statistical Areas for the 2018 Assessment

Primary Sampling Units (PSUs) for NAEP are classified as either metropolitan statistical areas¹ (metro areas) or non-metro areas. Metro area PSUs are those that are made up of counties in metro areas.

Each metro area constitutes a separate PSU, except when it crosses census region boundaries. Such metro areas are split along regional boundaries with each regional part considered its own distinct PSU. For example, the Louisville-Jefferson County, KY-IN metro area was partitioned into two PSUs, one for the counties in Kentucky which are part of the South region and the other for counties in Indiana which are part of the Midwest region.

In total, there were 372 metro area PSUs, 29 of which were defined as certainty PSUs. The remaining 343 metro area PSUs, covering a total of 859 counties, constituted the noncertainty portion of the 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 noncertainty metro area PSUs by census region. These estimates come from the county-level estimates of numbers of persons aged 0 to 17 from the 2015 U.S. Census Bureau population estimates.

Noncertainty metropolitan primary sampling unit (PSU) frame, by census region: 2018

Census region	PSUs	Counties	Youths	Mean number of youths per PSU
Total	343	859	30,017,328	87,514
Northeast	43	84	4,422,552	102,850
Midwest	91	229	7,009,814	77,031
South	141	454	13,076,698	92,743
West	68	92	5,508,264	81,004
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2018 Assessment. 1Based 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).

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