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 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.
