Prevalence is the proportion of a population that has a disease, condition, or risk factor at a particular point in time or over a specified period of time. It is a measure of the burden of diseases, conditions, and risk factors, while age-adjusted prevalence is a hypothetical number, which adjusts the prevalence based on the age distribution of another population (e.g., the 2000 U.S. Standard Population). When describing the burden of diseases, conditions and risk factors for the state, a region or a county, the prevalence should be used. When comparing the burden of disease among counties or regions, the prevalence should be reviewed first. If age is a risk factor for the disease and the age distributions are different among counties and regions, then look at the age-adjusted prevalence to determine if the difference or lack of difference in prevalence estimates is due to age.