Applied Epi Community

How to remember difference between incidence and prevalence

Hi everyone, thanks in advance for your help.

I still do not understand the difference between incidence and prevalence. It seems like many reports and books are using these words interchangeably. Does anyone have an easy way to remember the difference?

Hi @epi_dude, welcome to the forum. I’ll try to help you:

Incidence is a count of all NEW cases of a specific disease within a given time frame (week, month, year) and for a set geographic limit.

Prevalence is also measured within a specific set geographic limit, but is measured at a specific moment in time and tries to count ALL cases of that specific disease present in that population. All cases of disease means all old diagnosed cases and all new cases together. Because of this, incidence is calculated as a rate (number of new cases/period of time), whereas prevalence is a proportion (all cases of disease/total population).

As for how to remember the difference… :slight_smile: for me the term “incident” comes with associations of responding to an acute emergency such as a fire or train collision etc, so I remember incidence as taking place in one particular moment.

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One of my teachers taught me that -
Incidence” is like looking at a Movie, and
Prevalence” is like looking at Photo.

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