The incidence of a disease
is a statistical risk assessment, in a person or group of people, of developing this disease. Incidence is a branch of epidemiology. It is based on statistical studies. We define the incidence rate by giving the number of individuals likely to develop a particular disease out of a number of people (usually out of 100,000) in a given time period (usually one year). We can also talk about the incidence of a disease after the fact by saying for example that the incidence of influenza
was x per 100 000 in the US in 2012.