How to use this calculator
Label the event consistently, then enter the four cells of the 2×2 table.
Formula and method
Risk = events/group total; RR = risk₁/risk₀; OR = ad/bc. Log-scale intervals use normal critical values. Risk difference uses Newcombe Wilson limits.
Worked example
20/100 vs 10/100 gives risk difference .10, RR 2, OR 2.25 and NNH 10.
Assumptions and supported scope
Two independent groups and one fixed observation period. Log Wald RR/OR intervals; all cells receive +0.5 correction if any cell is zero. No stratification, confounding adjustment, person-time rates or causal inference.
Method references
Method and worked example checked against the calculator implementation. About our methods · Report a correction