What's the difference between 'incidence' and 'prevalence'?

What's the difference between 'incidence' and 'prevalence'?

Robert Friis (Chair, Health Sciences Department, California State University, Long Beach ) gives expert video advice on: What do epidemiologists mean by the term 'morbidity'?; What does 'etiology' mean? and more...

The incidence of disease refers to new cases of disease. Incidence information is used to study risk to the population, and also to study the ideology of diseases. Prevalence of disease refers to the total number of cases of disease that exist in the population, either during a period of time or at a specific point in time. Incidence and prevalence are related terms. As the duration of disease increases, for example, the prevalence of the disease must increase as well.