NAEP Technical DocumentationPrimary Sampling Unit Definition and Frame Creation for the 2001 National Main Assessment

The basic primary sampling unit (PSU) sample design for the 2001 assessment is a stratified probability sample with one PSU selected per stratum with probability proportional to population. A PSU can consist of the following:

a consolidated metropolitan statistical area (CMSA),
a metropolitan statistical area (MSA),
a New England county metropolitan area (NECMA),
a single county in the United States (including Alaska, Hawaii, and the District of Columbia), or
a group of contiguous counties in the United States.

A total of 94 PSUs per round were selected. PSUs that, because of their size, were drawn into the sample with certainty are common to the five rounds.

The PSU sampling frame for the 2001 assessment was constructed by grouping counties as specified by the following rules:

Each 1990 CMSA, and each MSA that was not part of a CMSA, was considered a separate PSU. In New England, NECMAs were the metropolitan PSU unit. (In New England, counties may split between two or more MSAs. A NECMA is a definition that approximates MSAs but consist of whole counties.)
Non-MSA PSUs were made to consist only of non-MSA counties. Whenever possible, each non-MSA PSU contained geographically contiguous counties with a minimum 1990 Census total population of 60,000 persons in the Northeast and Southeast regions, and 45,000 persons in the Central and West regions.
Region boundaries were not crossed in the definition of a PSU, not even in the case of MSAs. If a county in an MSA was in a separate region, it was taken out of the MSA and grouped with other contiguous counties in its region to define a PSU.

Checks were made to ensure that every county was included in one and only one PSU.

The 2001 PSU sampling frame contained 1,027 PSUs: 290 MSA PSUs, and 737 non-MSA PSUs.

Last updated 24 March 2008 (GF)

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