American Community Survey
What Is It?
The American Community Survey (ACS) is a nationwide survey from the U.S. Census Bureau that replaces the decennial census “long form” survey. Like the decennial long form it replaces, the ACS gathers information from a subset of the U.S. population. However, the ACS is conducted on a continual, monthly basis. This enables estimates from the ACS to be published every year, giving a more current view of the characteristics of the population and housing.
What Subjects Are Covered
The ACS collects information on a wide range of characteristics from a sample of persons and households in the U.S.
Key subjects include:
- Demographic (see a demographic sample)
- Social (see a social sample)
- Household composition and relationships
- Marital status and fertility
- School enrollment and educational attainment
- Place of birth
- Language spoken
- Economic (see an economic sample)
- Employment status, industry, and occupation
- Commuting to work
- Incomes and benefits
- Housing (see a housing sample)
- Occupancy and tenure (owner or renter occupancy)
- Home value and monthly housing costs
- Other housing characteristics such as size of structure and year built
What Is Published
ACS data are combined over different time periods and published by the U.S. Census Bureau annually in three series.
- 1-year estimates
- Data collected over a 12-month period
- Only for areas with populations of 65,000+
- Smallest sample, less reliable, most current
- Best used when:
- Recent estimates are more important than precise estimates
- Analyzing large populations
- 3-year estimates
- Data collected over a 36-month period
- Populations of 20,000+
- Larger sample, more reliable, less current
- Best used when:
- Analyzing smaller populations
- 5-year estimates
- Data collected over a 60-month period
- All geographic areas down to census tract or block group level — Note that the 5-year estimates are the only ACS estimates available at a neighborhood scale
- Largest sample, most reliable, least current
- Best used when:
- Accuracy is more important than having recent estimates
- Analyzing very small populations
What You Need to Know
There are some important ideas to keep in mind when using ACS data and products.
- Characteristics - ACS tells us about the characteristics of the population, not counts, because it is a done with a sample of the population.
- Period Estimates - ACS estimates reflect the characteristics of the population and housing over the entire period of time the data were collected, not for any particular point in the period.
- Margins of Error - ACS estimates carry margins of error which indicate how reliable the estimate is, with bigger margins of error signaling lower reliability.
To use the ACS responsibly, pay attention to margins of error and make a careful decision about whether the reliability of the estimates is high enough for your purposes.
- Margins of error can be quite large, especially for small areas and population groups.
- 1-year estimates generally have much higher margins of error than the multi-year estimates.
- Although more accurate, the 5-year estimates still tend to have higher margins of error than the decennial census long form estimates due to the lower sampling rates in the ACS
- Comparing Estimates - making comparisons using ACS data is complicated.
- Differences in estimates may not reflect actual differences, margins of error need to be considered.
- Although the ACS and past decennial census long forms cover similar topics, estimates for some should only be compared with caution or not at all.
What Else You Should Know
For a more detailed discussion of the issues involved with using ACS data please see the ACS data issues page.