American Community Survey
The American Community Survey (ACS) is an ongoing survey that asks questions about demographic, social, economic, and housing characteristics of the population. ACS differs from the decennial census because it is a period estimate—one that is collected over time—while the census is a point-in-time estimated collected on a single day, once every ten years. The ACS also collects much more information about individual and households than the 10-question, decennial census.
The sample for ACS includes 3 million addresses per year. Three data products are produced as a result of ACS sampling: 1-year for areas whose populations exceed 65,000; 3-year for areas with populations above 20,000; and 5-year for all areas, including census tracts and block groups. The 5-year product replaces the "long" form of the decennial census.
In December 2010, the Census Bureau for the first time released 5-year data, for the period 2005-2009. This is the first Census data available for small geographic areas (census tracts and block groups) since the 2000 census, and the good news is that the data will be refreshed every year from now on. Data for the period 2006-2010 is scheduled to be released by the end of 2011.
Because the sample size is small, however, the data has a considerably larger margin of error that must be considered when looking at individual numbers. And the fact that the data reflects a 5 year period means that it cannot be directly compared with the "snapshot" data from the decennial census.
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