What is the ACS?

The ACS is a project of the U.S. Census Bureau that will eventually replace the decennial census as the key source of information about American population and housing characteristics. The IPUMS database contains samples from the 2000-2006 ACS.

In every census since 1960, about 1-in-6 American households have received a "long form" census questionnaire (the source for the IPUMS samples). The long form consisted of more than 50 questions, while the short form contained only 7. Some respondents found the long form to be a burden, and the Census Bureau was concerned that the unpopularity of the long form contributed to declining response rates. Also, many users of Census Bureau products need annual data, rather than data for 10-year intervals.

The Census Bureau developed the ACS to address these problems. The ACS provides an annual snapshot of the American population similar to that provided by the decennial census long form. The Census Bureau has produced test data from the ACS since 1996. The 2000 ACS provided the survey's first nationally-representative data. If the ACS continues to be successful, the 2010 census will not include a long form questionaire.

How large are the samples?

The 2000 ACS is an approximately 1-in-750 public use sample consisting of 372,000 person records. Public use samples from the 2001-2006 ACS are even larger. The 2001-2004 samples are each represent approximately 0.4% of the population, including more than 1,000,000 person records per sample. The 2005 and 2006 ACS are full 1% samples containing more than 2,800,000 person records. The 2006 ACS is the first to contain group quarters. Researchers analyzing multiple ACS samples over time should remove group quarters cases, since they are available only in the 2006 data.

What variables are available?

The 2000-2006 ACS questionnaires are nearly identical to the 2000 census long form. The ACS samples also contain several questions on involvement in government programs and a fertility question not asked in the census. The downside of the 2000-2004 ACS samples is that they contain no geographic information below the state level. They do not identify PUMAs, cities, or metropolitan areas. The 2005 and 2006 ACS samples identify Public Use Microdata Areas (PUMAs) and metropolitan status (METRO). The IPUMS version of the 2005 and 2006 ACS provides the following additional geographic identifiers: CITY, METAREA, PUMASUPR, MIGTYPE1, MIGMET1, MIGCITY1, MIGPUMS1, PWTYPE, PWMETRO, PWCITY, and PWPUMAS. These variables were constructed at the University of Minnesota and are not available via the Census Bureau.

Is the ACS different from the C2SS?

No. IPUMS originally referred to the 2000 public use sample of ACS data as the Census 2000 Supplementary Survey (C2SS). Since we now have ACS data from 2001-2006, we refer to the C2SS as the 2000 ACS file.

How do I get the data?

Users can access the ACS data via the IPUMS data extract system.