Risk ratio (RR) is one measure of a treatment’s clinical effectiveness. If it is equal to 1, then the effects of the treatment are no different from those of the control treatment. If the RR is greater (or less) than 1, then the effects of the treatment are more (or less) than those of the control treatment. Note that the effects being measured may be adverse (e.g. death, disability) or desirable (e.g. stopping smoking).
