Incidence versus prevalence


           Incidence and proportion are both useful in describing disease frequency, but they serve different purposes. Incidence is useful for studying causes, prevention, and treatment of diseases by understanding infection patterns. Prevalence is useful for resources planning because it provides an indication of the disease burden in a population. For example, you may use the prevalence of STIs among teens to capture the scope of the problem and request attention and programmatic funding to the area, then use incidence to understand the risk within specific groups and when and how quickly infections are occurring in order to design interventions. Prevalence and incidence are closely linked. New cases (measured by incidence) always lead to higher prevalence. Even if incidence decreases, as long as there are new cases, prevalence will continue to increase unless the diseased are dying or being cured faster than new cases are occurring.