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PUMA
Public Use Microdata Area
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Description

PUMA identifies the Public Use Microdata Area (PUMA) where the housing unit was located. PUMAs are the smallest geographic units identified in Public Use Microdata Samples since 1990 for both the decennial censuses and the ACS/PRCS. To help maintain the confidentiality of respondents in public use microdata, every PUMA must, by design, have at least 100,000 residents at the time of the corresponding census.

IPUMS has also created PUMAs for the 1960 5% sample, which each correspond approximately to one or more 2000 PUMAs using a minimum population threshold of 50,000.

Note: PUMA codes are state-dependent. The PUMA codes for 1990 and later samples are unique only within each state, so a single code may identify different PUMAs in different states. To uniquely identify all PUMAs, it is necessary to combine the PUMA variable with a state identifier (STATEFIP or STATEICP). The IPUMS-defined 1960 PUMA codes are unique across all states and do not have this requirement.

The Census Bureau updates PUMA definitions with each decennial census, so PUMA codes may or may not identify consistent areas over longer periods of time. See the Comparability section for information about which PUMAs are used in each sample. See the Codes section for information about each set of PUMA definitions.

Note: In some multi-year samples, PUMA definitions vary or are allocated In multi-year ACS/PRCS samples that span a PUMA definition change, the identified PUMAs vary based on the survey year when each respondent was interviewed (as given by MULTYEAR). This occurs in samples that span the change from 2000 PUMAs (survey years 2000-2011) to 2010 PUMAs (survey years 2012-2021) and in the 2022 5-year ACS/PRCS sample (which uses 2010 PUMAs for survey years 2018-2021 and 2020 PUMAs in 2022). With the 2023 5-year ACS/PRCS sample, the Census Bureau began reporting only 2020 PUMAs for all survey years, which they achieved by assigning pre-2022 respondents a 2020 PUMA based on their 2010 PUMAs of residence and the known relationships between 2010 and 2020 PUMAs. The Bureau has provided no details on their PUMA allocation method, but IPUMS has confirmed that it produces plausible population totals for the assigned 2020 PUMAs.

In 1980 samples, "county groups" (CNTYGP98) are functionally similar to PUMAs with the same minimum population threshold of 100,000. In fact, "county group" is a misnomer because 1980 county groups, like PUMAs, typically subdivide large-population counties into smaller areas (though 1980 county groups still do not subdivide cities within counties as PUMAs do). In contrast, the county groups in 1970 samples (CNTYGP97) nearly all correspond to groups of one or more counties with a minimum population threshold of 250,000. In 1940 and 1950 samples, the identified geographic areas most like PUMAs are State Economic Areas (SEA).