The Virginia Behavioral Risk Factor Surveillance System Survey (BRFSS) is designed to provide stable and accurate estimates on key health outcomes for the household population of adults 18 years of age and older who reside in the Commonwealth of Virginia. The survey is not designed, however, to provide estimates by county. As such, the survey sample sizes are not sufficiently large to provide stable direct estimates of important health outcomes by county (or, in the case of Virginia, by independent city).
Small Area Estimation (SAE) often provides more reliable estimates for counties than can be obtained from direct survey estimates alone. SAE methods combine direct estimates of outcomes from the survey with estimates modeled using auxiliary or outside data. The BRFSS SAE method is one of several methods that can be used to produce reliable prevalence estimates in small geographic areas.