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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.  

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  • Only every 10 years, so is out-of-date quickly (-)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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