What does incidence mean?
Incidence is a noun meaning the rate or frequency with which something happens. It is especially important in medicine, public health, statistics, and insurance, where researchers distinguish the number of new cases of a disease from its overall prevalence, or how common the condition is at a given time. Outside these technical fields, incidence can simply mean an event or the fact of something occurring. Incidence also has a geometrical sense: it describes the relationship between lines or surfaces that meet at a point, as in the angle of incidence for a ray striking a mirror. The word is most useful when the question is not merely what happened, but how often it happens. In that sense, it is related to incident, coincidence, and accident through the Latin verb cadere, “to fall,” and its compounds involving the sense of something coming to pass.
nounThe frequency with which something occurs or is encountered, especially within a particular population or period. It can also mean the fact of something happening or, in geometry, the relationship between lines or surfaces that meet at a point.
- The frequency or rate at which something occurs, especially a disease or other measurable phenomenon.
- The fact of something happening or being encountered.
- In geometry, the relationship between lines, surfaces, or other geometrical objects that meet at a point.
"The incidence of the disease has declined since the vaccination programme began."
"Researchers recorded a sharp rise in the incidence of respiratory infections among school pupils."
"The angle of incidence determines how much light is reflected by the mirror."
The plural is used for separate instances or occurrences of something, especially in general rather than technical contexts.
"The report documented several rare incidences of equipment failure during the trial."
Incidence asks not only what happened, but how often—and where paths meet.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does incidence come from?
Incidence comes through Old French from Latin incidentia, meaning “an event” or “something that happens.” This was derived from Latin incidere, formed from in-, “upon” or “into,” and cadere, “to fall,” and originally conveyed something falling or happening. English later extended the word from individual occurrences to the frequency with which an event or condition occurs.
How incidence is actually used
In medicine and public health, incidence generally refers to the occurrence of new cases during a specified period. Prevalence, by contrast, measures how widespread a condition is in a population at a particular time.
Easily confused with incidence
An incident is a particular event, whereas incidence refers to how often something occurs or the relationship between intersecting lines.