Saturday, March 13, 2010

Introduction to the American Community Survey

© CQ Press 2011

The decennial census long-form sample, which was the source of social and economic data for geographic areas and population groups in the United States from 1960 to 2000, has been replaced by the continuous American Community Survey (ACS). Like the long form, the ACS provides data on the social, economic, and housing characteristics of the population from a sample of the nation’s households and group quarters. In several respects, the ACS represents a major advance over the census long-form sample by incorporating innovations that are meant to better address the information needs of the nation. These include the provision of data products for all geographic areas more than once a decade; the delivery of those products on a more timely basis—in the year after the data are collected; and the use of professional interviewers to help offset a decline in response and in the quality of data for many socioeconomic items on the long form.

Since 2005, the ACS questionnaire has been sent to a sample of about 240,000 addresses in every county of the nation. (See the attached timeline of major events in ACS History.) The sample is combined or “rolled-up” for 12 months to produce annual estimates of characteristics for places of 65,000 or more population. Thus, for large places in the nation, a socioeconomic portrait is now available on an annual basis. For places of 20,000 to 65,000 persons, 36 months of sample is the minimum required to provide estimates. These “three-year period estimates” tell us the average number of high school graduates or people who drive to work, for example, over that period. For the smallest places, those with fewer than 20,000 people, 60 months of sample is needed to produce “five-year period estimates,” which are averages for characteristics over a five-year period.

Like all innovations in their infancy, the ACS is a work in progress. The use of estimates for multi-year periods represents a new way of thinking about the way in which we paint portraits of the nation’s communities. Making comparisons across different geographic areas and measuring changes over time using these period estimates pose new challenges for all kinds of applications. Federal, state, and local officials, as well as members of the larger data user community, are now working on ways to incorporate these new data into policy formulation, needs assessments, and program planning and implementation. The challenge is how best to use these data, while dealing with issues regarding sample size, the addition of new variables to the survey, and changes in geographic boundaries over time.

The six entries in this new volume are designed to be a “what you need to know” about the ACS. There are two overarching entries on “ACS: Development to 2004” and “ACS: Implementation From 2005,” which are meant to document aspects of ACS history and evolution that can serve as a framework for understanding the conceptual underpinnings of the survey. The three entries on Questionnaire Content, Methodology, and Multi-Year Estimates are meant to provide a solid grounding in the basic “nuts and bolts” of the ACS. These entries include information on how the content development process works, the actual contents of the survey, some key aspects of the concepts and methods used to collect and compile the data, and the correct way to use multi-year estimates to compare different geographic areas. Finally, the Data Products entry provides information on the types of tabulations, profiles, and other specialized subject matter that are available from the ACS. This entry also provides information on where to find ACS data and the different pathways that are available to access the ACS.

Following the six entries is a combined bibliography, which is intended to provide the reader with a basis for further exploration on each topic. Together, the entries and the bibliography provide the reader with an essential primer on the ACS. Because the ACS program is in its infancy, data users need to pay careful attention to the ACS Web site, particularly the portion that documents errors in data products and any corrections (go to www.census.gov, then to American Community Survey, then to Data & Documentation, then to User Notes and Errata, which are left-hand buttons on the Documentation page).

Joseph J. Salvo

See also Long Form in the Encyclopedia of the Census, Second Edition

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