Incidence refers to the new cases of a disease.
The incidence rate of a disease is defined as the number of new cases of said disease that occur during a specified time period in a population at risk for developing the disease.
Incidence rate per population unit (x) =
(where x is a multiple of 100)
Note: If you want to know the incidence per 1000 population, substitute x with 1000. For incidence per 10,000 population substitute x with 10,000 and so on.
Considering the occurrence of disease as an event, incidence rate is a measure of events- disease is identified in previously disease free people who subsequently develop disease. Since incidence rate captures the transition from non-diseased state to diseased state, it is a measure of risk.
The incidence rate is comprised of two data elements- numerator and denominator (the multiplier is not data derived). We will look at numerator and denominator in turn.