incidence

incidence — noun

1. how often something, particularly an illness or unwanted event, occurs over a sp

1.nounB2
Definition

how often something, particularly an illness or unwanted event, occurs over a specific time period or within a particular group of people.

Example

The incidence of flu dropped sharply after the hospital started offering free vaccines.

incidence + of + disease; passive with drop/rise

Dr. Nikhil's team studied the incidence of heart problems among older factory workers.

study/track the incidence of [condition]

Common collocations
  • high incidence
  • low incidence
  • incidence of [disease]
  • reduce the incidence
  • incidence rate
Synonyms
  • frequency

    broader term for how often anything happens, not limited to negative events

  • prevalence

    in epidemiology, prevalence counts all existing cases at a point in time, while incidence counts only new cases

Grammar Patterns

incidence + of + noun phrase

Usage Note

Typically followed by of + a noun phrase naming the event or condition. Frequently modified by high or low. Common in academic and medical writing about population health.

Common Mistakes

The incidence of the car accident was high.
The incidence of car accidents in this area is high.
incidence refers to the rate of repeated events over time, not a single occurrence.

2. the way a beam of light meets or strikes a surface, considered as a physical eve

2.nounC1
Definition

the way a beam of light meets or strikes a surface, considered as a physical event.

Example

When sunlight enters water, the incidence of the light beam makes it change direction.

incidence of light — physics context

Physicists measure how the incidence of a laser on a prism changes the colours produced.

Common collocations
  • incidence of light
  • incidence of a beam
  • point of incidence

Grammar Patterns

incidence + of + light/beam/ray

Usage Note

Almost exclusively used in physics and optics contexts. The compound phrase angle of incidence is common in textbooks but functions as a fixed technical term.

Word family

Synonym discussion

Sense: noun/1

Incidence, frequency, and prevalence all describe how often something happens, but with important differences. Incidence is the most precise term in health and statistics — it counts only new cases appearing during a specific period. Prevalence is broader: it counts all existing cases (old and new) at a single point in time. Frequency is the most general of the three and works for any repeated event, positive or negative. For example, a public-health report might say the incidence of measles rose this year (new cases), the prevalence remains high in unvaccinated communities (total cases), and the frequency of clinic visits increased overall. Use incidence when you need to emphasize new occurrences within a defined timeframe, especially in formal or medical writing.

frequency ↗prevalence ↗occurrence rate

Common collocations

Nouns

Adverbs

Prepositions

Etymology

LatinFrenchEnglish

Incidence comes from the Latin word incidentia, meaning 'a falling upon'. That breaks down into in- (upon) and cadere (to fall). The word entered English through French in the 1400s, first carrying the literal sense of something falling or striking a surface — which is why the physics meaning (a ray of light 'falling upon' a surface) is historically the older sense. By the 1800s, the word had broadened to refer to the rate at which events 'fall upon' or affect a population, giving us the modern medical and statistical meaning.