What’s the Difference Between Incident, Incidence, and Instance?

This month, I have yet another rousing game of Which word should I choose? Today’s potentially confusing words are incident, incidence, and instance. As I’ve gathered examples for this piece, I’ll admit that repeatedly looking at these three words makes my head spin. They’ve all morphed into the same word, and I’m doubting everything I thought I knew. But we can keep them straight, I promise!

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An incident is an event or occurrence, and it often indicates something negative.

He was unconscious for 1 minute immediately following the incident.

Incidence is something’s rate of occurrence.

She asked for recommendations to decrease the incidence of malignancy at her age.

Here are the top 10 subjects that have a high incidence on the pediatric shelf exam.

An instance is an occurrence that is usually given as an example (For instance,…). It can also mean “case.”

Her mother reports that the girl had multiple instances of intense coughing that lasted several minutes last night.

Got it? Try some examples and see how you do:

Which of the following evidence-based strategies has been shown to reduce the [instance/incident/incidence] of developing ventilator-associated pneumonia?

Here we’re talking about a rate of occurrence of developing ventilator-associated pneumonia, so incidence is correct.

Let’s forget about the spilling-coffee-on-our-notes [incident/instance/incidence] during our AANP exam review session.

This example isn’t referring to a rate of occurrence, so let’s strike “incidence.” Coffee spilling on notes is an unfortunate event or occurrence—incident is correct.

He has six to eight [incidents/instances] of headache per month.

Does this one seem a little tricker? Let’s break it down. Is this patient describing six to eight unfortunate occurrences (incidents) or is he giving examples or stating the number of cases of headache per month (instances)? He’s mentioning several examples or cases, thus instances is correct.

If this feels overwhelming or confusing, you’re not alone. I usually have a gut reaction in examples like the ones above. For example, I may know right away that “instances” is correct, but then I start overanalyzing it and almost convince myself that “incidents” could be used.

Here’s one last challenge: can you fill in this tongue twister?

The [instance/incidence] of inciting [incidents/incidences] increased to eight [instances/incidents] per night.

The incidence (rate) of inciting incidents (negative events) increased to eight instances (occurrences) per night.

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If you have a hard time with these words—or really, any words—don’t fret! Remember: they’re just words, people mix things up all the time, and no one’s perfect. Consider that mantra my gift to you—say it as often as you need to.