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Boatwright Memorial Library

U.S. CENSUS DATA: Background & Choosing a Dataset

Background on The Census

U.S. Decennial Census of Population & Housing ("The Census")

  • Collected every 10 years, starting in 1790.
  • Goal is to count every single person living in the United States on April 1 of the Census year. 
  • The questions have changed over time. 

American Community Survey (ACS)

  • Complimentary survey to the Decennial Census; earliest available data is from 2005.
  • Sample of ~300,000 households per month on an ongoing basis. 
  • Data are released in two kinds of datasets:
    • 1-year estimates (includes data from 12 months of surveys) and
    • 5-year estimates (includes data from 60 months of surveys)
  • Questions are more detailed than those in the Decennial Census. Questionnaire for 2020 ACS: https://www2.census.gov/programs-surveys/acs/methodology/questionnaires/2020/quest20.pdf
  • Because the ACS is a sample survey, it has margins of error. There are also smaller areas that are not included in the datasets because of disclosure risk.  

Evolution of the American Census Data Viz

So, which should I use?

Which dataset/survey should I use? 

There are pros and cons to all of them, but here are some things to think about as you decide:

U.S. Decennial Census

Example: "Census 2010"; also sometimes labeled "DEC Summary File 1" or "DEC S.F. 1"
  • Most accurate (+)
  • Includes all geographies (+)
  • Only every 10 years, so is out-of-date quickly (-)
  • Limited scope of question topics (-)

ACS 5-year Estimates

Example: "ACS 2018 (5-Year Estimates)"; also sometimes labeled "ACS 2014-2018 5-year Estimates"
  • Broad scope of question topics (+)
  • Released every year, so usually more current than the Decennial Census (+)
  • Sample survey, so has a margin of error and does not include data for geographies where the population is smaller than 20,000 [citation]. (-)
  • Utilizes 5 years' worth of surveys, so more accurate than 1-year estimates (+)

ACS 1-year Estimates

Example: "ACS 2019"; also sometimes labeled "ACS 2019 1-year Estimates"
  • Broad scope of question topics (+)
  • Released every year, so usually more current than the Decennial Census (+)
  • Sample survey, so has a margin of error and does not include data for geographies where the population is smaller than 65,000 [citation]. (-)
  • Utilizes 1 year worth of surveys, so less accurate (with larger margins of error) than 5-year estimates (-)

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Paul Rosenstein
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