Prevalens

Prevalens is a term used in epidemiology to describe the proportion of individuals in a defined population who have a specific disease or condition at a given time or over a defined period. It can be measured as point prevalence, which refers to the proportion with the condition at a single moment, or period prevalence, which covers a defined interval such as a year. Prevalence is related to incidence (new cases) and to the duration of the condition: in a population in approximate steady state, prevalence roughly equals incidence rate multiplied by average disease duration, though real-world effects such as recovery, mortality, and migration can alter this relationship.

Prevalence is usually expressed as a proportion or percentage, and can also be reported per 1,000 or per 100,000 population. Data come from cross-sectional surveys, health registries, claims databases, or national statistics, with the denominator being the population at risk for the condition or the total population, depending on the definition.

Interpreting prevalence requires considering the time frame, population, and case definitions. It does not by itself indicate risk of developing the condition, and high prevalence can reflect long survival or high incidence. Limitations include underdiagnosis, misclassification, changes in diagnostic criteria, and unequal access to care.

Prevalence informs public health planning, resource allocation, and burden assessment. It is often complemented by incidence data and by measures such as age-standardized prevalence to allow comparisons across populations.

Note: Lifetime or cumulative prevalence refers to the proportion of individuals who have ever had the condition by a certain age.