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Core-based statistical area size

Codes and Frequencies

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CBSASZ identifies the population size of the core based statistical area (CBSA) in which the household is located. CBSA's are classified as either metropolitan or micropolitan statistical areas, but micropolitan areas are too small to be identified in the CPS public use microdata, so CBSASZ provides sizes of metropolitan areas only.

Users should note that official definitions of metropolitan areas have changed over time. Please see the comparability tab for more details.

The Census Bureau publishes records of re-categorized or newly introduced metropolitan areas on its Historical Statistical Area Delineations page.


The concept of a Core-Based Statistical Area (CBSA) first came into use in 2003 and was used as the statistical area to define the population size variable in CPS samples beginning in May 2004.

As the Census Bureau explains, "the general concept of a CBSA is that of a core area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that core". More specifically, CBSAs "consist of the county or counties or equivalent entities associated with at least one core (urbanized area or urban cluster) of at least 10,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties with the counties associated with the core." Under this definition, CBSAs include metropolitan statistical areas and smaller micropolitan statistical areas (which are too small to be identified in the CPS public use microdata).

For all samples between September 1995 and May 2004, and 1988 to 1994 ASEC samples, the CPS metropolitan area size variables were based on pre-CBSA definitions of metropolitan areas, which consisted of three types of areas: metropolitan statistical areas (MSAs), primary metropolitan statistical areas (PMSAs), and consolidated metropolitan statistical areas (CMSAs). IPUMS-CPS supplies population sizes for these earlier areas through the variables MSACMSZ and MSAPMSZ.

Between May 2014 and July 2015, users may notice different CBSA sizes within the same metropolitan area. This is due to a new set of geographic areas being phased in as households enter the survey under a new sample design. For more information, see Appendix E of the 2016 ASEC codebook.

The Census Bureau provides a number of resources describing in more detail the measurement of metropolitan statistical areas, including a Geographic Terms and Concepts factsheet, a Metropolitan and Micropolitan factsheet, and a chapter on Metropolitan Areas in the 1994 Geographic Areas Reference Manual.

Comparability with IPUMS-USA

For the classifications mentioned above in the variable description, IPUMS-USA and IPUMS-CPS are fully comparable. A final broad category, "State Unknown," appears in some IPUMS census samples but is used in only a small number of miscoded cases in the early years of IPUMS-CPS.


  • All households and group quarters.


Years Jan Feb ASEC Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2004 - - - - - X X X X X X X X
2005 – 2016 X X X X X X X X X X X X X
2017 X X X X X X X X X X X - -


This variable has no flags.