Prevalence

In epidemiology, the term prevalence quantifies the proportion of a population with disease or a particular condition at a specific point in time (sometimes called point prevalence). Prevalence is used widely in the media and by government agencies, insurance companies, epidemiologists, and health care providers. Often confused with prevalence, incidence (described in [Page 838]detail elsewhere) quantifies new cases while prevalence describes existing cases.

While the term prevalence rate is often used synonymously with prevalence, the strict definition restricts prevalence to a proportion, not a rate. The difference is in the denominator: Rates describe risk of disease during a given time interval among a population at risk, while proportions describe the likelihood of disease at a specific point in time among the population. The point in time ...