Relative risk (RR)

The relative risk is the risk of one group divided by that of the other. 1 means no difference; 0.5 means the risk is half as large. The interval is calculated on the log scale after Katz.

Example: RR = 0.58, 95% CI [0.47, 0.72]: the risk in the compared group is 0.58 times the risk of the other.

Caution: With an empty cell the RR is not estimable; Statable does not correct silently. It applies to cohorts and experiments, not to case-control studies.