ABSTRACT
One way to distinguish between incidence and prevalence is to regard incidence as the rate at which cases first appear, while prevalence is the rate at which all cases exist. To illustrate the difference between incidence and prevalence, consider that the incidence of influenza in a community might be low because no new cases had developed. Yet a measure of the disease's prevalence could be a larger figure because it would represent all persons who are currently sick from the illness. For chronic health disorders such as cancer, cases initially reported in terms of incidence for a particular period may be reported later as prevalence because the duration of the disease has caused it to exist for a longer period of time. The cases are simply no longer new. Therefore, the use of data on disease determines whether an analysis should be one of incidence or prevalence. An epidemiologist would use cases denoting incidence if he or she were analyzing the outbreak of a health problem. Cases specifying prevalence would be used to study the overall extent of a disorder.
