Risk Ratio & Confidence Interval
Calculate an unadjusted risk ratio and approximate log-Wald interval from two independent groups.
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Compare risks for two independent groups observed over the same outcome window. Defaults are fictional. Enter participants with and without the event, not total participants in the non-event fields.
Calculation results
Risk ratio: 0.5
Group A risk: 12%. Group B risk: 24%.
Approximate 95% log-Wald interval: 0.264941 to 0.943606.
Method and limits
RR = [a/(a+b)] ÷ [c/(c+d)]. SE(log RR) = √[1/a − 1/(a+b) + 1/c − 1/(c+d)]. Limits = exp(log RR ± 1.959964 × SE). This unadjusted comparison does not establish causation. It is inappropriate for case-control sampling, paired or clustered observations, or unequal risk windows. Zero cells are rejected rather than silently corrected. No survival censoring is handled.
Cochrane: effect measures and calculations · Read the practical guide · Download blank worksheet (TXT)