Rate ratio explained

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:

RateRatio = (IncidenceRate1)/(IncidenceRate2) ^[1] where incidence rate is the occurrence of an event over person-time (for example person-years):IncidenceRate = (events)/(persontime) The same time intervals must be used for both incidence rates.

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

• Odds ratio
• Ratio
• Risk ratio

Notes and References

1. Web site: Rate Ratio. www.ctspedia.org.
2. Web site: Bellan. Steve. Study Design and Analysis in Epidemiology: Where does modeling fit?. 8 April 2012.