Demographics

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Fairfax, VA 22035

Research Tools

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Which Data Should I Use?

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.

 

Fairfax County
Decennial Census
American Community Survey
Research Tools

 

FAIRFAX COUNTY DATA

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:

  • Estimates and Forecasts for Fairfax County or a sub-area of the county.
    • Overall Population
    • Housing Units by Type of Value
    • Overall Number of Households
  • Owned Housing Market Value
  • Rental Housing Inventory, Costs and Vacancy Rates
  • Existing Land Use
  • Commercial and Industrial Gross Floor Area by Type

Data sources:

Demographic Reports
Demographic Interactive Mapper
For Rent

 

DECENNIAL CENSUS DATA

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:

  • Population estimates for a decennial census year
  • Persons by race or ethnicity estimates for a decennial census year
  • Persons by age and/or sex for a decennial census year

Data sources:

Decennial Census Summaries

 

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 data when I need:

  • Population Characteristics
    • Educational Attainment
    • Occupation
    • Health Insurance Coverage
    • Poverty Status
  • Household Characteristics
    • Household and Family Income
    • Language Spoken
  • Community or Census Designated Place population or household characteristics information

Data sources:

ACS Summaries

 

Survey Research Tools

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.

Man Thinking

Overview of Sampling Procedures

Charts

Survey Questionnaire Design

Data Stream

Common Pitfalls in Conducting a Survey

 

American Community Survey (ACS) Tools

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.

Excel

Percent Change Calculator

 

Excel

Statistical Significance Calculator

Excel

Coefficient of Variation (CV) Calculator

Excel

Combining Estimates and Calculating the Associated Margin of Error (MOE)

Excel

Calculating Percents and the Associated Margin of Errors (MOEs) from Estimates

 

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