Morbidity Frequency Measures
Prevalence (Prevalence Rates)
Prevalence is the proportion of people in a population who have a particular disease at a specified point in time, or over a specified period of time.
- The numerator includes not only new cases, but also old cases (people who remained ill during the specified point or period in time). A case is counted in prevalence until death or recovery occurs.
- This makes prevalence different from incidence, which includes only new cases in the numerator.
- Prevalence is most useful for measuring the burden of chronic diseases such as tuberculosis, malaria and
HIV in a population. The formula for calculating prevalence is: