Re: What is the difference between prevalence rate and incedence rate.

Prevalence and incidence describe two different situations.
Consider a rather large number of people, such as the inhabitants of your 
city (I hope you do not live in a very small town), and considerer 
influenza (as far as I know, we are in winter).
To know the prevalence of influenza requires a "one-day" study, i.e. you 
have to examine all the people of your city, count the number of people who 
are at that time ill, and compute the ratio. Prevalence is: number of ill 
people / number of inhabitants.
On the other hand, incidence of influenza is the number of cases of 
influenza, on a one year basis, related to the number of inhabitants.
As you see, prevalence and incidence are diferent indicators wich correlate 
to acute and endemic diseases.

Hope this helps

Luc

Luc A. Ronchi, MD
Paed Anaesth
Centre Hospitalier de Saint Nazaire
France