Relative Risk, Odds Ratio & NNT Calculator
From a 2×2 table (exposure × outcome), compute relative risk, odds ratio, absolute and relative risk reduction, and number needed to treat — each with a 95% confidence interval.
2×2 table (exposure × outcome)
For education/research reference — verify against statistical software before publication. Computed locally.
Interpreting the numbers
An RR or OR of 1.0 means no association; above 1 means increased risk/odds, below 1 means reduced. A confidence interval that crosses 1.0 is not statistically significant. Pair relative measures with the absolute ones (ARR, NNT) — a large relative effect can still be a small absolute one.
Frequently asked questions
What is the difference between relative risk and odds ratio?+
Relative risk (RR) is the ratio of the probability of the event in the exposed vs unexposed group. The odds ratio (OR) is the ratio of the odds. RR is intuitive for cohort/RCT data; OR is used in case-control studies and logistic regression, and approximates RR when the outcome is rare.
How is NNT calculated?+
NNT = 1 ÷ absolute risk reduction (ARR), where ARR is the difference in event rates between groups. It is the number of patients you need to treat to prevent one additional event; smaller is better.
What confidence intervals does this use?+
RR and OR use the standard log-transform method (Katz for RR, Woolf for OR) with a 95% interval. Wide intervals crossing 1.0 indicate a non-significant association.
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