(September 2005) The U.S. government has a long history of gathering information about the American people. Congress has authorized funds to conduct a national census of the U.S. population every 10 years since 1790, as required by the U.S. Constitution. When the first American leaders chose to allocate congressional seats to states according to population size, a decennial census was mandated to obtain a complete and official enumeration of the population. The first census recorded a minimum of information: the gender, race, and age group of household members. Census questionnaires have changed every decade since then, reflecting the current interests and needs for information about the U.S. population and housing units. Some censuses collected detailed demographic, social, and economic information for all Americans, including parents’ birthplaces, dates of immigration and naturalization, literacy, and the value of any assets. More recent censuses consist of a “short form” delivered to all U.S. housing units and a “long form,” delivered to a sample of housing units. The short form includes questions about age, gender, race, Hispanic origin, household relationship, and owner/renter status; the long form seeks detailed socioeconomic information about U.S. population and housing.

The 21st century marks a new era in census taking and a break with tradition. The American Community Survey (ACS), a relatively new survey conducted by the U.S. Census Bureau, is ushering in the most substantial change in the decennial census in more than 60 years. The ACS is a nationwide monthly survey designed to provide communities with reliable and timely demographic, housing, social, and economic data every year. The ACS will replace the 2010 Census long form by collecting detailed information throughout the decade. While the primary aim of the census is coverage— obtaining a complete population enumeration—the ACS program is focused on content—obtaining accurate information about population and housing characteristics. The ACS data will provide, for the first time, a continual stream of updated information for states and local areas, and may revolutionize the way federal, state, local, and tribal governments plan, administer, and evaluate their programs.

Beginning in 2006, the ACS will provide population and housing data for areas with populations of 65,000 or more. Assuming sufficient congressional funding, the ACS will have sampled 15 million addresses by 2009; by 2010, the ACS will provide five-year averages of demographic, housing, social, and economic data for the nation, states, cities, counties, and even smaller geographic areas. These five-year moving averages will then be updated annually and will provide, for the first time, the ability to monitor social and economic trends in local communities in years between decennial censuses.

This Population Bulletin presents an overview of the ACS and the new opportunities and challenges it offers. It explores ways the survey can help monitor socioeconomic trends in the United States. The ACS provides several advantages over the decennial census and other surveys:

  • The ACS will deliver relevant data, comparable to the census long form, updated every year rather than once a decade.
  • The ACS is the first nationwide survey that can be used to monitor annual trends in local communities, and make valid comparisons among communities in the years between censuses.
  • The ACS will provide new information about U.S. migration levels and trends.
  • The ACS estimates will be more accurate than those from the census long form through the use of professional, highly trained interviewers to collect information from households that do not return complete forms.

The continuous measurement approach of the ACS also presents several challenges for people who want to use and interpret the data. For example:

  • The ACS sample will be smaller than that of the 2000 Census long form because of the high cost of conducting a monthly survey.
  • Researchers, journalists, and others working with ACS results will need to learn how to interpret 90 percent confidence intervals, which show the margin of sampling error around the estimates.
  • The ACS includes several questions that are similar to those collected in other federal surveys for other purposes—especially the Current Population Survey (CPS), the American Housing Survey (AHS), and the Survey of Income and Program Participation (SIPP). Hence, users must choose when to use the ACS and when to use one of the other sources of population and housing characteristics.
  • Data users will need to learn how to interpret the five-year moving averages that form the core of the ACS estimates. Interpreting a moving average can be especially tricky in areas with rapidly changing populations.
  • Funding for the ACS must be renewed every year, making it vulnerable to budget cuts and fluctuations that could jeopardize the program or the usefulness of the data.

Mark Mather is deputy director of Domestic Programs at the Population Reference Bureau, where he coordinates several projects that communicate population research to advocacy groups, educators, journalists, and the public. Kerri L. Rivers is a research associate and program administrator for Domestic Programs at the Population Reference Bureau. Linda A. Jacobsen is director of Domestic Programs at the Population Reference Bureau.