When Fairfax County and the Census Bureau estimates are compared they often differ because different methodologies and techniques are used to produce them. Here are some guidelines to help data users decide which data source is best to use based on the information you need.
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 data when I need:
Health Insurance Coverage
Household and Family Income
Community or Census Designated Place population or household characteristics information
The following brochures are intended to highlight various sampling procedures and their uses, provide guidance when developing and testing survey questionnaires, and review potential survey research problems. These brochures were produced by Economic, Demographic and Statistical Research, Fairfax County Department of Management and Budget.
The following tools are intended to help data users calculate percent change, statistical significance, coefficients and margins of error (MOE) when working with multiple ACS estimates. These tools were produced by Economic, Demographic and Statistical Research, Fairfax County Department of Management and Budget.