# What is the difference between period prevalence and incidence rate?

I am confused about the difference between period prevalence and incidence rate. Following are from Wikipedia:

The incidence rate is the number of new cases per population in a given time period.

Period prevalence is the proportion of the population with a given disease or condition over a specific period of time.

Thanks!

• First one is NEW, second one is ALL as I understand. So, first is a derivative of second by time. – sashkello Aug 9 '13 at 5:50