ACS vs. Summary File 3

The American Community Survey (ACS), which replaces the Census long form Summary File 3 (SF3), is a primarily mail-based household survey conducted by the U.S. Census Bureau with an annual sample size of about 3.5 million addresses and a response rate said to exceed 97 percent. Like SF3, it produces estimates for numerous social, economic, and housing characteristics. These estimates are summarized for geographic areas ranging from neighborhoods to Congressional districts to states to the entire nation. The smallest geographic entity presented is at the Census Block Group level.

The ACS shares many similarities with SF3. However, there are many differences. The chief advantage of ACS data is its far more frequent release. It collects responses continuously instead of every ten years. This gives planners at all levels of government, business, and the general public far more current data than the decennial long form, and provides for the first time information about temporary populations, such as beach and ski communities.

But this advantage is also a disadvantage. While the ACS is timelier, information is also smoothed (flattened) out and has a lower accuracy rate because it is conducted over years of time instead of at a single point in time. This is particularly prevalent for small geographic areas which must pool three or five years of data to accumulate a large enough sample for reliable estimates.

There are also differences in residence rules, boundaries and definitions of geographic areas, how and which questions are asked, and survey methodology.

Our pdACS2013 package is available for those wanting to try out the new ACS data.

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