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For the past several years the Census Bureau has released data products from the American Community Survey (ACS) in the form of 1-year estimates. These estimates were based on data collected in a single calendar year and describe the average characteristics for that specific year. For example, the 2007 ACS estimates generally describe the average social, economic, demographic, and housing characteristics for calendar year 2007. In December 2008, the Census Bureau introduced ACS multiyear estimates, specifically 3-year estimates. These estimates are based on data collected over a 3-year period of time and therefore they describe the average characteristics for that 3-year time period. In 2009, the 2008 ACS 1-year estimates were released in September and the 2006-2008 ACS 3-year estimates were released in October. The table below summarizes some key features of the most recent ACS 1-year and 3-year estimates.
Are based on data collected between January 2008 and December 2008.
Are published for selected geographic areas with populations of 65,000 or greater.
Are based on a smaller sample size and are therefore less reliable than the 3-year estimates.
Are more current than the 3-year estimates.
Are based on data collected between January 2006 and December 2008.
Are published for selected geographic areas with populations of 20,000 or greater.
Are based on a larger sample size and are therefore more reliable than the 1-year estimates.
Are less current than the 1-year estimates.
Both ACS 1-year and 3-year estimates can be accessed using the American FactFinder (AFF). The 3-year estimates are summarized for users as tables and maps using many of the same data products as the 1-year estimates such as detailed tables, data profiles, and thematic maps. Public Use Microdata Sample (PUMS) files are released on a slightly later schedule than the other data products but once released, are also available in both 1-year estimate and 3-year estimate versions through AFF. Both 1-year and 3-year summary files are available through the ACS FTP site.
Information on this page provides you with a greater understanding of multiyear estimates in general and explains how and when they should be used. Additional information about how to use and understand ACS data can be found in The ACS Compass Products, a series of educational materials that include audience-specific handbooks and fully scripted PowerPoint presentations. The handbooks include a detailed set of technical appendices with more information to help you navigate 1-year and 3-year estimates.
What is an ACS multiyear estimate?
What types of geographic areas are published for the 1-year and 3-year ACS?
Four things you should know about how ACS multiyear estimates are produced
Choosing between ACS 1-year and 3-year estimates