Understanding the Census

Decennial Census vs. American Community Survey

The annual estimates from the Census Bureau are not the same, or as complete, as the information produced from the Census every 10 years.

Decennial Census

Census 2010 logo

  • The bureau’s best, most reliable data comes from Census each 10 years.
  • Every effort is made to reach each household to complete a Census form with basic information.
  • The Census form (pdf) was reduced to 10 questions in 2010, basically asking the age, gender, race, housing and family relationship questions.
  • Of note:
    • No longer is there a “long form,” which used to go to one-in-six housholds.

American Community Survey

American Community Survey logo

  • The best resource for recent data on a wide variety of topics. See a sample American Community Survey form (pdf).
  • The bureau releases annual estimates for larger places based on a survey.
  • Data is released annually for places of at least 65,000, and all places down to the census block level for rolling five-year periods. (Note: The Census Bureau in 2015 discontinued its three-year survey estimates for places of at least 20,000.)
  • Of note:
    • Like any survey of a sample of people, there is a margin of error. The first releases for the neighborhood and small town level – providing a rolling average estimate for 2005-09, proved to have very large margins of error in some cases.
      • Take care to check the margin of error released with each number to judge whether conclusions should be drawn for rankings and other purposes.
      • This is especially true where a small number of people fit a particular demographic.
    • When it is not important to use data from the most recent year, consider instead getting data from the 5-year estimates. The data is a bit older, but the margins of error are much smaller because more people have been surveyed.
    • Do not mix 1-year and 5-year American Community Survey information. The numbers usually will be different.
    • Do not use the American Community Survey for population estimates. The survey understates the total population for most places because it is a snapshot of the people reached for the survey. The Census Bureau provides separate population estimates.

Population Estimates

Census taker in 1930

A Census Bureau enumerator records information from a woman with 10 children in 1930. (Photo courtesy of the Census Bureau)

The Census Bureau each year produces population estimates for each township, village, city, county and state.

The best estimates are done for counties. Here’s how it is done.

However, these estimates are not as good as the census count every 10 years. It’s good to know how the estimates are conducted so you can determine whether the “more recent” estimates should be used.

State populations

State population estimates are simply the sum of each county’s population.
County populations. The Census Bureau takes into account a variety of information.

  • Births, based on recorded births.
  • Deaths, based on recorded deaths.
  • Migration for those under age 65, based on federal income tax returns.
  • Migration for those 65 and over, based on Medicare enrollees.
  • Net international migration, based on information from Census Bureau surveys, Census 2000 and military movement records.

City, village and township populations

The bureau follows these steps, a less accurate process than what is done for the counties.

  • Creates a new housing unit estimate for each place by taking into account:
    • Number of housing units from Census 2000.
    • Estimating new units constructed since 2000, based mainly on new housing permits.
    • Estimating units lost based on previous trends. For 2008, the estimate was based on the trend found in the 1997-2000 American Housing Survey.
  • Multiplies the new estimate of housing units for each place by the 2000 Census number of residents per household for each place.
  • Multiplies the result by the Census 2000 occupancy rate for each place.
  • This results in a preliminary estimate. An adjustment is made by following these steps:
    • Sums the preliminary population estimate for each place in a county.
    • Each city, village or township is then adjusted up or down at the same rate countywide so the population for all the places equals the previously released, and more precise, county population estimate.
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