Incident / Incidence
Different meaningsAn incident is an individual event; incidence describes the occurrence or frequency of events in a defined context and may be reported as a count, proportion or rate.
Incident
Use when
You mean one event or occurrence, especially an unusual, harmful or reportable one.
Example
“The system recorded three security incidents in July.”
Incidence
Use when
You mean the occurrence or frequency of something in a defined population, group or period, expressed as a count, proportion or rate.
Example
“The incidence of account lockouts fell to 1.4 per 1,000 logins.”
Quick check
three incidences when three events are meant, incidence count without a population or period, incidence rate without a denominator or period, incident used for a population rate
Usage note
For an incidence count, state the population or context and period. For an incidence proportion or rate, also state the denominator. Specialised writing may use incidences for separate measures, but use incidents when simply listing individual events.