The relative risk, or risk ratio, compares the probabilities of an event in two groups. If the event probabilities in the exposed
and unexposed groups are 
and 
, respectively, then
 |
A relative risk of 1 indicates equal event probabilities, a value greater than 1 indicates greater risk in the first group, and a value below 1 indicates smaller risk. This interpretation concerns association and does not by itself establish causation.
Relative risk differs from the odds ratio 
. The two are close for rare events
but can differ substantially otherwise.
