PREVALENCE

n. commonness, state of being widespread, currentness, predominance

In epidemiology, the prevalence of a disease in a statistical population is defined as the total number of cases of the disease in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population. For example, the prevalence of obesity among American adults in 2001 was estimated by the U. S. Centers for Disease Control (CDC) at approximately 20.9%. In plain English, "prevalence" simply means "proportion" (typically expressed as a percentage).Prevalence is useful because it is a measure of the commonality of disease. It helps physicians with the probability of certain diagnoses and is routinely used by epidemiologists, health care providers, government agencies, and insurance companies.
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Noun
1. the quality of prevailing generally; being widespread; "he was surprised by the prevalence of optimism about the future"
(hypernym) generality
(hyponym) currency
(derivation) prevail, persist, die hard, run, endure
2. (epidemiology) the ratio (for a given time period) of the number of occurrences of a disease or event to the number of units at risk in the population
(hypernym) ratio
(classification) epidemiology
3. a superiority in numbers or amount; "there is a preponderance of Blacks in our prisons"
(synonym) preponderance
(hypernym) number, figure
(derivation) predominate, dominate, rule, reign, prevail

n. prevalence, predominance

(n.)
The quality or condition of being prevalent; superior strength, force, or influence; general existence, reception, or practice; wide extension; as, the prevalence of virtue, of a fashion, or of a disease; the prevalence of a rumor.