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U.S. Census Demographic Data: American Community Survey

A guide to finding and using population data from the U.S. Census Bureau

How is the ACS different from the Decennial Census?

The socioeconomic, housing, and financial information that used to be collected with the Decennial Census Short Form is now provided by the American Community Survey (ACS), since 2005. The 2010 Census shows the number of people who live in the U.S. and the American Community Survey shows how people live.

The ACS is a sample survey of roughly 2.9 million households; therefore the data are estimates with a margin of error.

The ACS provides period estimates. That is, it estimates average characteristics of people over 1-year, 3-year, and 5-year periods, rather a point-in-time estimate like the 2010 Census.

Data availability depends on the population size of the geographic area of interest.  Smaller areas, such as block groups, are only available in 5-year estimates.

1-year, 3-year, and 5-year estimates

1-year estimates 3-year estimates 5-year estimates
12 months of collected data 36 months of collected data 60 months of collected data
Data for areas with populations of 65,000+ Data for areas with populations of 20,000+ Data for all areas
Smallest sample size Larger sample size than 1-year Largest sample size
Less reliable than 3-year or 5-year More reliable than 1-year; less reliable than 5-year Most reliable
Most current data Less current than 1-year estimates; more current than 5-year Least current
Best used when Best used when Best used when

Currency is more important than precision

Analyzing large populations

More precise than 1-year, more current than 5-year

Analyzing smaller populations

Examining smaller geographies because 1-year estimates are not available

Precision is more important than currency

Analyzing very small populations

Examining tracts and other smaller geographies because 1-year estimates are not available

From the U.S. Census Bureau, [ACS] Guidance for Data Users.

ACS Data

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