American Community Survey basics
What is the ACS?
Every 10 years since 1790, Congress has authorized the government to conduct a national census of the U.S. population, as required by the United States Constitution. In the twentieth century, the questions were divided between short and long form. The short form was conducted on a 100% sample of the U.S. population, while the long form was done on a 1-in-6 sample of the population and consisted of a much wider selection of questions.
After the 2000 Census, this long form became the ACS. Sent to approximately 3.5 million addresses per year, it is the largest household survey administered by the Census Bureau. Unlike the census, which is conducted once every ten years, the ACS is conducted annually and throughout the entire year, and while the census is considered to be a snapshot of the population, the ACS is much more like a video with its continually updated data.
How are ACS data collected?
The Census Bureau selects a random sample of addresses to be included in the ACS and mails questionnaires to approximately 295,000 addresses a month across the United States. ACS forms are not mailed to specific people, but rather to specific addresses. The sample is designed to ensure good geographic coverage and does not target individuals. The survey takes place all year, and interviews, where necessary, are conducted by permanent staff – not the temporary workers who interview people for the decennial census.
The ACS comes in two releases: 1-year and 5-year estimates. The 3-year estimates were discontinued in 2013. The 1-year file is released for areas of at least 65,000 in population, the 3-year file was released for areas of at least 20,000, and the 5-year file for all of the areas for which the long form was released (block-groups, tracts and higher).
What data can you expect to find in the ACS?
The ACS covers a wider selection of topics in comparison to the decennial census.
| Demographic Characteristics | Social Characteristics | Economic Characteristics | Housing Characteristics |
|---|---|---|---|
| age, sex, Hispanic origin, race, and relationship to householder |
marital status, fertility, ancestry, place of birth, citizenship, year of entry, educational attainment, veteran status, and disability |
income, food stamps benefit, labor force status, place of work, journey to work, vehicles available, industry, occupation, and class of worker |
tenure, housing value, rent, selected monthly owner costs, year the structure was built, units in structure, rooms, bedrooms, house heating fuel, telephone service available, and farm residence |
What is the data used for?
The ACS is taken every year to provide more consistent ongoing information and allow the census to focus on counting the population. This data is used by many public-sector, private-sector, and not-for-profit stakeholders to allocate funding, track shifting demographics, plan for emergencies, and learn about local communities. Businesses use ACS estimates to inform important strategic decision-making. For example, someone scouting a new location for an assisted-living center might look for an area with a large population of seniors and a large proportion of people employed in nursing occupations. If a person wants to see how they compare with their neighbors or find a new place to live, they can look to the ACS to provide a wealth of information. The ACS provides useful statistics pertaining to the median income of an area, the median age of the residents, the median house value, and monthly household expenses.
Certain drawbacks come with the data — for instance, the five-year file includes data from both before and after the financial crisis of 2007-08. As was the case with the long form, the community survey is a sample, and hence, subject to sampling error. The confidence interval is often expressed as percent or number plus or minus another number that defines the interval. On the other hand, benefits include data—even for small areas—that is never more than a few years out of date. In conclusion, despite some differences between the American Community Survey and the old census long form data, the survey is in many ways far superior. Not only is the data released more often and in a more timely fashion, but the numbers may also be more accurate since the survey is conducted by a permanent interview staff.
When to use 1-year, 3-year, or 5-year estimates
The ACS provides many advantages over the information collected in the past through the decennial census long form samples. The main benefits of the ACS are timeliness and access to annual data. The ACS delivers useful, relevant data, similar to data from previous census long forms, but updated every year instead of every 10 years. However, the main challenge for ACS data users is understanding and using multiyear estimates.
1-year estimates
- cover 12 months of collected data; for example, from January 1, 2016 to December 31, 2016
- data is collected for areas with population of more than 65,000
- most current data
- less reliable than 3- and 5-year estimates
- annually released: 2005-present
Best used when you're looking for currency and not precision, want to analyze smaller populations and smaller geographies.
3-year estimates
- cover 36 months of collected data; for example, from January 1, 2011 to December 31, 2013
- data is collected for areas with a population of more than 20,000
- larger sample size and more reliable, but less current than 1-year
- more current, but less reliable than 5-year
- annually released: 2007-2013
The Census Bureau stopped producing ACS 3-year estimates from 2013 onward. The ACS 3-year estimates from 2005 to 2013 remain available to users.
Best used when looking for more precise data, analysing smaller populations and smallet geographies.
5-year estimates
- cover 60 months of collected data; for example, from January 1, 2011 to December 31, 2015
- data is collected for all areas, which makes this the largest sample size
- most reliable, but least current
- annually released: 2009-present
Best used when looking for precision and not currency, analyzing very small populations, tracts and other smaller geographies.
The American Community Survey (ACS) is a flagship data collection effort aimed at almost 300,000 U.S. households every month. Head over to this blog post to learn more about the history of the ACS and the political challenges that it faces today.