2. Measurements of incidence
2.1. Incidence proportion (cumulative incidence)
Incidence proportion is the proportion of an initially disease-free population that develops the disease or experiences a health event during a specified period of time[1]. The denominator of an incidence proportion is the number of persons at the start of the observation period.
For an incidence proportion, the numerator is the number of new cases of a disease or health event that occur during a given time period, while the denominator is the total specified population at risk during the defined study period. To accurately measure incidence proportion, all individuals at risk for the health event under study must be followed during the entire study period. Because complete follow-up is required to directly compute incidence proportion, it is usually only calculated for studies with a short follow-up period.
[1] Resource available at: Lesson 3: Measures of Risk | CDC Archive