American Community Survey (ACS) Questions and Answers

1. What is the American Community Survey (ACS)?

   The ACS is a household survey developed by the Census Bureau to replace the long form of the decennial census program. The ACS is a large demographic survey collected throughout the year using mailed questionnaires, telephone interviews, and visits from Census Bureau field representatives to about 3 million household addresses annually. Starting in 2005, the ACS produced social, housing, and economic characteristic data for demographic groups in areas with populations of 65,000 or more. (Prior to 2005, the estimates were produced for areas with 250,000 or more population.) The ACS also accumulates sample over 3-year and 5-year intervals to produce estimates for smaller geographic areas, including census tracts and block groups.

   Period estimates represent an area’s characteristics for the specified period of time and may be thought of as averages for the period. Estimates are scheduled for release following the calendar year in which the data were collected, as shown in the table below.

   ACS estimates release schedule

   Population size   of area	Data   product	Calendar year
   		2007	2008	2009	2010	2011	2012	2013
   65,000+	1-year estimates for data collected in	2006	2007	2008	2009	2010	2011	2012
   20,000+	3-year estimates for data collected in			2005-2007	2006-2008	2007-2009	2008-2010	2009-2011
   All areas *	5-year estimates for data collected in				2005-2009	2006-2010	2007-2011	2008-2012

   * Five-year estimates will be available for areas as small as census tracts and block groups.



2. What estimates are produced from the ACS?

   Each year, the ACS produces estimates on characteristics of the population for the nation, States, and cities and counties with 65,000 population or more. Topics covered by the ACS are virtually the same as those covered by the census long-form sample data. Estimates are produced for demographic characteristics (sex, age, relationship, households by type, race, and Hispanic or Latino ethnicity), social characteristics (school enrollment, educational attainment, marital status, fertility, grandparents caring for children, veteran status, disability status, residence one year ago, place of birth, U.S. citizenship status, year of entry, world region of birth of foreign born, language spoken at home, and ancestry), economic characteristics (employment status, commuting to work, occupation, industry, class of worker, income and benefits, and poverty status), and housing characteristics (housing occupancy, units in structure, year structure was built, number of rooms, number of bedrooms, housing tenure, year householder moved into unit, vehicles available, house heating fuel, utility costs, occupants per room, housing value, and mortgage status and costs).

3. Does the ACS develop labor force estimates?

   Yes, the ACS includes questions about work and search for work so that some measures of labor force activity are available, along with the other social and economic data collected in the survey.

4. How does the ACS compare with the Current Population Survey?

   The Current Population Survey (CPS), jointly sponsored by BLS and the Census Bureau, is a monthly sample survey of about 60,000 households designed specifically to produce the current monthly employment and unemployment data and the annual data on income and poverty for the nation. CPS monthly employment and unemployment estimates are available within a few weeks of the end of the reference period—the calendar week including the 12th of the month. ACS annual employment and unemployment estimates are available about 9 months after the end of the reference year. The monthly CPS estimates are a key input to the Local Area Unemployment Statistics (LAUS) program conducted by BLS, which produces the official labor force statistics for States and substate areas. Employment and unemployment estimates from the ACS and CPS can differ because the surveys use different questions, samples, and collection methods.

5. How does the ACS reference period relate to the reference period in the CPS?

   The CPS reference period is typically the week including the 12th of the month, with interviews being conducted the following week (typically the week including the 19th of the month). CPS data are produced and published monthly. Annual average data are also developed at the end of the calendar year. The CPS uses a fixed reference period, as compared to the ACS, where the reference period is the week prior to when a respondent answers the survey. CPS interviews are conducted in the course of a single designated week each month, whereas respondents answer the ACS at times that vary throughout the month and year. ACS respondents are initially contacted by mail. If they do not return their survey within a month of receiving it, they are then contacted by phone. Approximately 1 in 3 households that still do not provide answers is sub-sampled for an interviewer to contact them in person in the third month.

6. Are there differences in the labor force estimates from the ACS and the CPS?

   Yes. In 2009, the numbers of persons the ACS classified as “employed,” “unemployed,” and “not in the labor force” for the nation were all higher than the official CPS estimates. The ACS unemployment rate was 9.9 percent, compared to the CPS annual average of 9.3 percent.

7. Are there differences in the labor force estimates from the ACS and the LAUS program?

   Yes. In 2009, the numbers of employed individuals in the ACS were higher than the LAUS estimates in 26 States and lower in 24 States and the District of Columbia. The employment level differences ranged from +4.52 percent in Alabama to -3.24 percent in Washington, with a weighted-average difference of +0.61 percent. The ACS-based unemployment levels were higher than the LAUS estimates in 42 States and the District of Columbia and lower in 8 States. The unemployment level differences ranged from +31.82 percent in Nebraska to -14.15 percent in Rhode Island, with a weighted-average difference of +8.39 percent. The ACS unemployment rates were higher than the LAUS rates in 39 States and the District of Columbia, lower in 9 States, and the same in 2 States. The unemployment rate differences ranged from +1.8 percentage points each in Arkansas and New Hampshire to -1.6 points in Rhode Island. The ACS and LAUS unemployment rates were the same in both Iowa and South Carolina. See the table (TXT or PDF) for differences between the ACS and LAUS estimates for States in 2009.

8. What accounts for the differences between ACS and CPS-LAUS estimates?

   A number of factors may account for the difference in the estimates, including the following: overall questionnaire differences, differing requirements in the two surveys with regard to whether an individual is actively looking for work, and differing reference periods, modes of collection, and population controls.

   The underlying concepts and definitions of all labor force data developed from the LAUS program are consistent with those of the Current Population Survey (CPS). Monthly estimates for all States and the District of Columbia are produced using estimating equations based on time-series and regression techniques. These “signal-plus-noise” models combine current and historical data from the CPS, the Current Employment Statistics (CES) program, and State Unemployment Insurance (UI) systems. A tiered approach to estimation is used. Model-based estimates are produced for the nine Census divisions that geographically exhaust the nation. (These models use inputs only from the CPS.) The division estimates are benchmarked to the national levels of employment and unemployment each month. The benchmarked division model estimate is then used as the benchmark for the States within the division. In this manner, the sums of the State estimates of unemployment and employment equal the national estimates for these measures.

9. What are the questionnaire differences?

   The ACS questions relating to labor force activity are less detailed than those in the CPS. For example, the ACS uses seven questions in determining labor force status, while the CPS uses sixteen. There are more detailed, probing questions in the CPS regarding employment status. In addition, the CPS information is always collected by trained interviewers and never through mail questionnaires.

   Effective 2008, changes were made to the ACS questionnaire that modified and improved existing questions for several subject areas. (A summary of the changes made to the 2008 ACS can be found at ACS Design and Methodology.) In particular, revised labor force questions were introduced to better capture data on employment status. The modifications had the impact of increasing the estimated number of employed persons from the ACS relative to CPS and LAUS estimates.

10. How do the job search questions differ?

    The ACS instrument asks people if they are looking for work and available to take a job if offered one, but does not ask about the nature of the job search. The CPS questionnaire probes to see if people are actively looking for work (interviewing, calling contacts, etc.) versus passively looking for work (for example, looking at want ads in the paper). In the CPS, a person is unemployed only if that person has actively searched for work.

11. How can the ACS rolling reference period affect the estimates?

    ACS responses can relate to any weekly period throughout the year and reflect different economic events. Respondents can choose to delay completion of the ACS form.

    ACS data are collected over a range of time periods. In the ACS, the reference is to activity in the “last week” whenever the respondent fills out the survey. In the CPS, the reference period is fixed for the calendar week including the 12th of the month. A varying reference week and time of data collection could be particularly problematic for shorter, transitory statuses or activities that could be influenced by seasonal variation. Unemployment, for example, is a state that is subject to both seasonal and cyclical variability.

12. What is the mode-of-collection effect?

    The mode of collecting data also may affect the labor force estimates. All CPS interviews are conducted through personal visits or telephone calls by Census field representatives using laptop computers for data entry. ACS data are collected primarily by mail using “paper and pencil” questionnaires, with telephone and personal visit collection used as follow-up to mail nonresponse. Data collected using paper forms do not have interviewers assisting respondents in interpreting questions.

13. What population controls are used in the two surveys?

    Both the ACS and CPS are sample surveys used to make estimates for a larger population. Each person in the survey represents a larger number of similar individuals in the population. To do this, each survey utilizes population estimates produced by the Population Estimates Program at the Census Bureau. Each year, the Population Estimates Program publishes population estimates by demographic characteristics (age, sex, race, and Hispanic or Latino ethnicity) for the nation, States and counties. The reference date for estimates is July 1st.

14. Does the LAUS program plan to utilize the ACS data in its estimating procedures?

    LAUS has no immediate plans to utilize ACS data in monthly estimation. We are, however, investigating ways in which the ACS data can be used in place of the data from the decennial census long-form survey that have been utilized in updates to program benchmarks after decennial censuses.

15. Where can one obtain more information about the ACS?

    More information is available from the Census Bureau via American FactFinder or at the American Community Survey website.

Last Modified Date: May 4, 2011

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