We've had a number of questions from our clients as to why the CDXZipStream demographic feed from the American Community Survey doesn't include data down to the zip code level. It does include data for larger geographies like state, county, and "places" (the Census Bureau's version of city, town, borough, etc.) but zip code data seems to be a glaring omission.
To understand this, we need to talk a little bit about how the American Community Survey (ACS) works. The ACS is a survey that has been performed by the U.S. Census Bureau every year since 2005; it has replaced the old "long form" that used to be part of the decennial (10-year) census. Starting in 2010, the decennial census now only consists of the "short form" that covers basic questions about age, gender, race, and household size. The more interesting demographic data such as income, educational attainment, and other socioeconomic factors are now being obtained exclusively through the ACS.
Each year the ACS surveys about 3 million U.S. households, and in order to get statistically valid demographics for smaller geographies like zip codes, the data must be combined over a five year period – there just isn't enough data for a single year to get an accurate picture for a zip code. In fact, one year data is applicable only to geographies with a population of 65,000 or more, and the three year combined data included in CDXZipStream is applicable to geographies of 20,000 or more. Since the ACS formally started in 2005, five year data (covering the period 2005 through 2009) will be released for the first time in early December 2010; it will be available in CDXZipStream within two weeks after its release.
So what's the big deal? The real advantage of the annual American Community Survey is that it will show a true moving picture of American demographics that could never be provided by the 10 year "snapshot" of the decennial census. Zip code demographics from here on out will be updated annually using data from the last five surveys, and trends can be measured using real data instead of relying on error-prone models based on extrapolations of old data. So stay tuned ... we expect demographics by zip code will be available in CDXZipStream by the end of 2010.