About the American Community Survey
The American Community Survey (ACS) is an ongoing survey conducted by the U.S. Census Bureau since 2005. In 2010, the ACS replaced the decennial census long form as the source of sample data for population and housing indicators. The short form of the decennial census is still distributed to obtain a count of the entire U.S. population.
ACS has asked questions about age, sex, race, family and relationships, income and benefits, health insurance, education, veteran status, disabilities, employment location and mode of travel to work, place of residence, price paid for living essentials. You can review the annual questionnaires to see the precise questions asked each year.
There are both benefits and challenges associated with replacing the long form with ACS. The primary benefit is the freshness of data: ACS data is collected every year, whereas the decennial census was collected every ten years. Challenges include a higher sampling error for the ACS, due to a smaller sample population, and difficulties comparing data from year to year.
Each year, the Census Bureau releases 1-, 3- and 5-year estimates based on information gathered in the ACS.
In deciding which estimate you want to use, you should consider the currency of data; the geographic size of your population; and the acceptable sample size/reliability of the data. The Census Bureau chart below shows distinguishing features of the different estimates. Tract-level data is not available for ACS 1-year or 3-year estimates.
Important note: if you wish to compare ACS estimates to earlier decennial census data, please review these cautions first.
|
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 |
Finding ACS Data & Information
ACS data is incorporated into data.census.gov, the Census Bureau's primary data tool, with a variety of access points:
UC San Diego affiliates can find ACS data and maps in the Social Explorer database.
UC Library Search lists several ACS briefs and reports, most of which are available online.
The Census Bureau's Technical Documentation page includes information about more advanced issues such as code lists, data suppression, and table/geography changes.
