ncommon events in populations, such as the occurrence of specific diseases, are usefully modelled using a Poisson distribution. A common application of Poisson confidence intervals is to incidence rates of diseases (Gail and Benichou, 2000; Rothman and Greenland, 1998; Selvin, 1996).
The incidence rate is estimated as the number of events observed divided by the time at risk of event during the observation period.