The American Community Survey (ACS) is an ongoing statistical survey by the U.S. Census Bureau. It regularly gathers information previously contained only in the long form of the decennial census, such as ancestry, educational attainment, income, language proficiency, migration, disability, employment, and housing characteristics. These data are 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. Sent to approximately 295,000 addresses monthly (or 3.5 million per year), it is the largest survey after the decennial census that the Census Bureau administers.
From the 1940 census through the 2000 census, a subset of all Americans received a "long form" containing additional questions. Many Americans found filling out the long form to be burdensome and intrusive, and its unpopularity was a factor in the declining response rate to the decennial census. In 1994, the Bureau began the process of changing the means of obtaining the demographic, housing, social, and economic information from the census long form to the ACS. Testing began in 1995, and the ACS program began producing test data in 2000, 2001, and 2002.
The survey was fully implemented in 2005. The following year, the Census Bureau released estimates for all areas with populations of 65,000 or more using the data collected from January to December 2005. In 2010, the ACS produced its first set of estimates for areas of all population sizes, using information collected from January 2005 through December 2009.
The American Community Survey cites 13 U.S.C. § 141 and 13 U.S.C. § 193 as the authority to request survey responses. In 2002, the GAO concluded that the Bureau has authority to conduct the survey and "require responses from the public."
The ACS has an initial sample of approximately 3.5 million housing unit addresses and group quarters in the United States, with sample selected from all counties and county-equivalents, American Indian and Alaska Native area, and Hawaiian Homeland, and in Puerto Rico annually. Data are collected primarily by mail, with follow-ups by telephone and personal visit. Approximately one third of those who do not respond to the survey by mail or telephone are randomly selected for in-person interviews, and the final response rate for that group was 97.3 percent in 2012. Because approximately two-thirds of mail/telephone nonrespondents are not selected for in-person follow-up interviews, the ACS only includes approximately 2 million final interviews per year. In 2012, completed ACS interviews represented 67.1 percent of the housing units initially selected for inclusion in the sample.
Like the decennial census, ACS responses are confidential. Every employee at the Census Bureau takes an oath of nondisclosure and is sworn for life to not disclose identifying information. Violations can result in a 5-year prison sentence and/or $250,000 fine. Under 13 U.S.C. § 9, census responses are "immune from legal process" and may not "be admitted as evidence or used for any purpose in any action, suit, or other judicial or administrative proceeding."
The Census Bureau aggregates individual ACS responses (i.e. microdata) into estimates at many geographic summary levels. Among these summary levels are legal/administrative entities such as states, counties, cities, and congressional districts, as well as statistical entities such as metropolitan statistical areas, tracts, block groups, and census designated places. Estimates for census blocks are not available from ACS.
In order to balance geographic resolution, temporal frequency, statistical significance, and respondent privacy, ACS estimates released each year are aggregated from responses received in the previous one, three, or five calendar years:
ACS estimates are available via a number of online data tools. The American Fact Finder (AFF) is the primary tool for disseminating ACS data, allowing users to drill down to specific tables and geographies (starting with 2013 estimates, AFF also includes block group data). A selection of the most popular tables are shown in the QuickFacts, Easy Stats, Census Explorer, and OnTheMap tools for 5-year estimates, and My Congressional District for 1-year estimates. The Summary File is the most detailed data source, and is available as a series of downloadable text files or through an API for software developers.
Custom cross-tabulations of ACS questions can be made using the Public Use Microdata Sample (PUMS), freely accessible through Integrated Public Use Microdata Series. PUMS data contain responses to every question from a sample of respondents. To protect respondent privacy, PUMS data are anonymized and only available down to areas containing 100,000 people or more known as Public Use Microdata Areas (PUMAs). The analysis of all ACS microdata without the sampling and anonymization in PUMS is restricted to qualified researchers at secure Federal Statistical Research Data Centers (FSRDCs).
Those who favor the American Community Survey argue that census questions beyond head count have existed since 1790. All individual American Community Survey responses are kept private and are used (along with other ACS responses) to create estimates of demographic characteristics for various geographies. Because of data swapping techniques to ensure confidentiality, it is impossible to figure out how individual people responded based on data from published ACS estimates.
American Community Survey data provides important information that cannot be found elsewhere, and thus it is important that the ACS exists, as the federal government, as well as various businesses, researchers, and local governments use ACS data for planning and decision-making purposes.
The Department of Commerce has stated that those who receive a survey form are legally obligated to respond to the ACS. Those who decline to complete the survey may receive follow-up phone calls and/or visits to their homes from Census Bureau personnel. 13 U.S.C. § 221 imposes a fine of not more than $100 for refusing or willfully neglecting to answer questions posed by census takers and a fine of not more than $500 for willfully providing false information.
To date, no person has ever been prosecuted for refusing to answer the ACS. Former Director of the Census Bureau Kenneth Prewitt remarked that the Department of Commerce is "not an enforcement agency" and that "the Department of Justice would have to do the prosecution, and we don't recommend that." The Census Bureau prefers to gain cooperation by convincing respondents of the importance of participation, while acknowledging that the mandate improves response rates (and thus accuracy) and lowers the annual cost of survey administration by more than $90 million.
The survey asks for more information, and at a higher frequency, than the simple enumeration required by U.S. Constitution Article I Section 2. Despite the GAO's conclusion that the Census Bureau has the authority to conduct the survey under 13 U.S.C. § 141 and 13 U.S.C. § 193, several U.S. representatives have challenged the ACS as unauthorized by the Census Act and violative of the Right to Financial Privacy Act. Rep. Ron Paul of Texas, who opposes the ACS, said of it that the founding fathers of the United States "never authorized the federal government to continuously survey the American people."