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U.S. Census: Decennial Census to American Community Survey

What Time the Data Covers

Period estimate

  • ACS describes a period
  • Taken continuously throughout the year
  • “An estimate that describes the average characteristics of an area over a specific time period”


  • The Census is a point in time
  • Snapshot

Change From Decennial Census to ACS


Decennial Census, 1940-2000

Everyone filled out the short form and a random sample filled out the "long form," which included the short form.

Short form = 100%

Sample size very large, 17 to 18%

The decennial census will continue to collect short form data.

 2010 Census only had short form


ACS (American Community Survey) estimates *

Replaces the decennial Census "long form."

Data collected all through year.

The ACS is collected by mail, telephone, and visits.

Addresses are chosen at random within areas.

5-year, 3-year, and 1-year estimates* are produced.

The sample size is 2.5% of households per year. The Margin of Error for the data is large.

Multiple years of data create more reliable estimates for smaller locations.

Measures the characteristics, not counts of the population.


* Estimates is the appropriate term; the Census is a count.



If only population estimates are needed, use the data from the Population Estimates Program (PEP).

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