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Rate ratio

From Wikipedia, the free encyclopedia

In epidemiology, a rate ratio, sometimes called an incidence density ratio or incidence rate ratio, is a relative difference measure used to compare the incidence rates of events occurring at any given point in time.

It is defined as:


where incidence rate is the occurrence of an event over person-time (for example person-years):

The same time intervals must be used for both incidence rates.[1]

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.[2]

See also[edit]


  1. ^ a b "Rate Ratio". www.ctspedia.org.
  2. ^ Bellan, Steve. "Study Design and Analysis in Epidemiology: Where does modeling fit?". Retrieved 8 April 2012.