Prevalence

There are two types of prevalence in epidemiology:
– Point Prevalence: The proportion of individuals in a population who have a condition at a specific point in time.
– Period Prevalence: The proportion of individuals who experience a condition over a specified time period.
These measures differ from incidence because they include both new and existing cases. In the steady state (no epidemics) and when the prevalence in the population is quite low, Prevalence (P) and Incidence (I) are related: P = I x D, where D is the average duration of the disease. Cross-sectional surveys, such as population censuses, give detailed information on the prevalence of conditions or risk factors, but are less likely to be useful in describing the natural history or progression of a condition. In economic evaluation, budget impact analyses tend to rely on prevalence information, whereas cost-effectiveness analyses are generally applicable to incident cohorts (with new developing or progressing disease).