Rate ratio
A rate ratio in epidemiology, is a relative difference measure used to compare the incidence rates of events occurring at any given point in time. A common application for this measure in analytic epidemiologic studies is in the search for a causal association between a certain risk factor and an outcome.
Where incidence rate is the occurrence of an event over person-time, for example person-years.
Note: the same time intervals must be used for both incidence rates.
