Which Data Should I Use?

When estimates from Fairfax County and the Census Bureau are compared they often differ.  The estimates differ because different methodologies and techniques are used to produce them.  Here are some guidelines to help data users decide which data source to use.

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Fairfax County Taking Measure Map Graphic

Fairfax County

Fairfax County produces annual small-area and county-level estimates and forecasts. Point-in-time data as of January 1.

Most reliable when I need:

Census In Your Hands Graphic

Decennial Census

Every ten years, the U.S. Census Bureau conducts a complete count of the nation's residents creating small-area and county-level estimates.  Point-in-time data as of April 1.

Most reliable when I need:

Compass Graphic

American Community Survey (ACS)

Ongoing survey conducted by the U.S. Census Bureau providing small-area and county-level estimates. Flow estimates over a period of time - one-year and five-year periods. Avoid mixing one and five year data. One-year ACS data are more current but do not provide large enough sample sizes to generate small area estimates. Use one-year data when county-level information is desired. Use five-year data when sub-county information is desired.

Most reliable when I need:


Contact Fairfax County: Phone, Email or Twitter | Main Address: 12000 Government Center Parkway, Fairfax, VA 22035
Technical Questions: Web Administrator

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