incidence

American  

[in-si-duhns] / ˈɪn sɪ dəns /

noun

1. the rate or range of occurrence or influence of something, especially of something unwanted.

   the high incidence of heart disease in men over 40.

2. a falling upon, affecting, or befalling; occurrence.

   The incidence of murder that Sunday afternoon shocked the sleepy village.

3. Optics, Physics.

   1. the striking of a ray of light, beam of electrons, etc., on a surface, or the direction of striking.

   2. angle of incidence.

4. the fact or the manner of being incident.

5. Geometry. partial coincidence of two figures, as of a line and a plane containing it.

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incidence British  

/ ˈɪnsɪdəns /

noun

1. degree, extent, or frequency of occurrence; amount

   a high incidence of death from pneumonia

2. the act or manner of impinging on or affecting by proximity or influence

3. physics the arrival of a beam of light or particles at a surface See also angle of incidence

4. geometry the partial coincidence of two configurations, such as a point that lies on a circle

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Etymology

Origin of incidence

First recorded in 1375–1425; late Middle English, from Late Latin incidentia. See incident, -ence

Explanation

Incidence means the frequency with which something bad occurs. You’ll hear of “incidences of cancer” or “incidences of war." You hope the incidence is decreasing, not increasing. You might confuse incidence and incident. They sound similar, but incident refers only to something that happened, not to the frequency with which it happens. After a car accident, the police file an incident report, which is a fancy way of saying they write down what happened. Looking at these reports grouped together can show you if the incidence of accidents at specific intersections in town is on the rise.

Example Sentences

The higher dosage of misoprostol required when it’s used alone can also lead to a greater incidence of benign but uncomfortable side effects like nausea and diarrhea.

From Slate • May 18, 2026

“These viruses are also what are called ‘low incidence, high consequences,’” said Robert Cross, a hantavirus researcher and assistant professor of microbiology and immunology at the University of Texas Medical Branch at Galveston.

From MarketWatch • May 7, 2026

Since 1982, when records began, incidence and mortality rates for cervical cancer in Australia have both halved.

From BBC • May 1, 2026

"Public investments that expand access to enriching environments, like libraries and early education programs designed to spark a lifelong love of learning, may help reduce the incidence of dementia."

From Science Daily • Apr. 15, 2026

A more detailed comparison of the incidence of wars before and after 1945 might help to clarify this question.

From "Cosmos" by Carl Sagan

Related Words

• extent
• frequency
• percentage
• prevalence
• proportion
• rate