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