Rate ratio

A rate ratio (sometimes called an incidence density 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.^[1]

$\text{Rate Ratio} = \frac{\text{Incidence Rate 1}}{\text{Incidence Rate 2}}$ ^[2]

Where incidence rate is the occurrence of an event over person-time, for example person-years.

$\text{Incidence Rate} = \frac{\text{events}}{\text{person time}}$

Note: the same time intervals must be used for both incidence rates.^[2]

See also

• Ratio
• Risk ratio
• Odds ratio

References

1. Bellan, Steve. "Study Design and Analysis in Epidemiology: Where does modeling fit?". Retrieved 8 April 2012.
2. http://www.ctspedia.org/do/view/CTSpedia/RateRatio