I recently created a data extract comprised of 2023 ACS data. The data extract was restricted to cases from Connecticut (STATEFIP=9) only. I was using the Excel file found in this website to determine which codes from the COUNTYFIP variable correspond to Connecticut’s nine county-equivalent planning regions (Changes to Counties and County Equivalent Entities: 1970-Present). After a second look at the data extract, I realized that there aren’t any cases in the 2023 ACS that represent two of Connecticut’s nine county-equivalent planning regions. The missing regions are the Capitol Planning Region (COUNTYFIP=110) and Northeastern Connecticut Planning Region (COUNTYFIP=150). Could this be an issue with the data download? Or were these regions truly not captured in 2023 ACS data?
While the variable COUNTYFIP identifies counties or county equivalents such as Connecticut Planning Regions, the comparability tab for COUNTYFIP notes that IPUMS USA cannot identify all counties in recent samples. This is because the ACS Public Use Microdata File (PUMS) that IPUMS USA harmonizes does not report the county (or planning region in the case of CT) that a respondent resided in; state and PUMA (Public Use Microdata Area) are the only geographic identifiers provided. Where PUMA and county boundaries are coterminous, IPUMS USA identifies the county that PUMA residents resided in. More specifically, the protocol assigns all respondents in a given PUMA to a county if and only if the county was coterminous with a single PUMA or the county contained multiple PUMA, none of which extended into other counties. All of Connecticut’s eight counties were identified in the IPUMS ACS samples from 2006-2021. IPUMS USA replaced identification of Connecticut’s historical counties with Planning Regions starting with the 2022 ACS. However, the country-wide change in PUMA boundaries by the Census Bureau in 2022 combined with the shift in boundaries from county to planning regions affected identification.
In the case of Connecticut’s Capital Planning Region, it appears that though Connecticut PUMAs 20201, 20202, 20203, 20204, 20205, 20206, and 20207 closely follow the borders of the region, Connecticut PUMA 20203 excludes around the town of Stafford (see map below obtained from the IPUMS USA 2020 PUMA definitions page). As a result, around 11,000 total people who live in the black circled area are officially in the Capital Planning Region, but are only identified as residing in Connecticut PUMA 20301 (this translates to roughly 1.2% of the total population of the Central Planning Region). This is because PUMAs are designed to contain a population of at least 100,000 in order to protect the privacy of respondents. Since the population of the Northeastern Planning Region is slightly below this threshold, the Census Bureau assigned it a part of the neighboring region. Due to this mismatch, we do not assign respondents to either the Capital or the Northeastern Planning regions since this will cause county-level estimates to diverge from Census Bureau published estimates that use their internal file.
You might identify respondents who reside in the Capital Planning Region, sans Stafford, using the seven combined PUMAs listed above. However, you should be aware how this will affect your final estimates. If you do not require individual-level microdata, you can obtain geographically aggregated ACS summary data for all counties and county equivalents through our spatial data project, IPUMS NHGIS.
