Our Microsoft Excel add-in, CDXZipStream, contains demographic data feeds based on data from the American Community Survey. The ACS is a survey performed by the U.S. Census Bureau which has replaced the old “long form” of the 10-year census. Please see our article ZIP Code Census Demographic Data in Microsoft Excel about our newest data feed, CDXACSZCTA, which provides for the first time comprehensive ACS data based on ZIP code.
Since the American Community Survey is performed annually, all the ACS data feeds in CDXZipStream are updated annually too. However, the smaller the geography, the longer the span of data required. For small geographies like census tract and ZCTA, the data must be aggregated over a five-year period to get statistically significant results; as of this writing the most recent set of five year data spans the years 2007 to 2011. Therefore, in these cases every annual update does need to incorporate some older data as well.
For some geographies, such as places (or cities), deciding what span of data to use is a balance between including as many geographies as possible versus using the most recent data. For CDXZipStream feeds, here are the data spans we use, along with the number of geographies for each feed:
State: 1-year data, 52 geographies (all states, including Washington D.C. and Puerto Rico)
CBSA’s*: 5-year data, 955 geographies (all CBSA’s)
Counties: 5-year data, 3,221 geographies (all counties)
Places (Cities): 3-year data, 3,128 geographies (only places with populations greater than 20,000)
ZCTA’s**: 5-year data, 33,120 geographies (all ZCTA’s)
All geographies were not included for places (cities), excluding those with populations of less than 20,000. In this case, it is generally a better choice to use ZCTA’s, which do cover a smaller population (averaging about 8,000) and is generally an easier index to use due to the availability of zip codes.
*CBSA’s (Core Based Statistical Areas) are the U.S. Census Bureau term for an urban area of at least 10,000 people.
**ZCTA’s (ZIP Code Tabulation Areas) are the U.S. Census Bureau version of a ZIP Code area. For more information please see our article What’s a ZCTA?