Group Comparison Calculator

based on example shown in  Evidence-based Medicine (Sackett, Richardson,Rosenberg,Haynes) page 230, Churchill Livingstone, publishers.

Group 1 Group 2
No of patients with event (r1) No of patients with event(r2)
No of patients in group (n1) No of patients in group (n2)

Proportion (%) of patients with event in group 1 (p1)
Proportion (%) of patients with event in group 2 (p2)
Absolute risk reduction (ARR)  = p2-p1 (%)
Standard Error (SE) of ARR;
95% Confidence Interval (CI) for ARR = ARR + 1.96*SE -
Numbers Needed to Treat (NNT) = 100/ARR
95% CI for NNT = 100/CI for ARR -
Relative Risk (RR)  = p1/p2
95% CI for RR -
Relative Risk Reduction (RRR)  = 1-RR (%)
95% CI for RRR = 1- CI for RR -
Odds Ratio (OR) = r1(n2-r2)/r2(n1-r1)
95% CI for OR -