Prevalence

Synonyms

Period prevalence; Point prevalence

Definition

Prevalence is the percent of persons in a population with a certain condition. Prevalence combines both preexisting cases and incident cases together to form a numerator, which is then divided by the total population being studied. Like incidence, prevalence must be calculated for a specified time frame. If that time frame spans a broad range of time (i.e., a year, 10 years, etc.), then prevalence over that time frame is referred to as a “period prevalence.” If the time frame is relatively short, then the prevalence measure is often called “point prevalence.”

An example of when point prevalence would be measured would be visiting a clinic and counting the number of children with and without ASD on that day. Cases of ASD could be children who were diagnosed with ASD on that day, as well as children who had been previously diagnosed. Point prevalence is often compared to a photograph: data are collected all at once (or over a brief...