Relative Risk Calculator

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Cell a: people in the exposed group who experienced the outcome.
cases
Cell b: people in the exposed group who did not experience the outcome.
cases
Cell c: people in the unexposed group who experienced the outcome.
cases
Cell d: people in the unexposed group who did not experience the outcome.
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Confidence level for the RR interval. 95% is the clinical standard.
Relative risk (RR)Increased risk
2
Risk in exposed30%
Risk in unexposed15%
CI lower bound1.149
CI upper bound3.482
P-value (two-tailed)0.0143
Absolute risk difference (ARR)15%
NNT / NNH6.7
Odds ratio (OR)2.429
Attributable fraction (exposed)50%
Risk (exposed)30%
Risk (unexposed)15%

The exposed group is 100% more likely to experience the outcome (RR = 2).

  • Risk in the exposed group is 30% versus 15% in the unexposed group, an absolute difference of 15 percentage points.
  • The 95% confidence interval for RR is (1.149, 3.482). The interval excludes 1, suggesting a statistically significant association.
  • Two-tailed p-value: 0.0143, which is below the conventional 0.05 threshold.
  • Number Needed to Harm (NNH): approximately 7 people, the number who must be exposed (or treated) for one additional outcome to occur (or be prevented).

Next stepAssociation is not causation. Confounding, bias and chance can all shift a risk ratio. Pair this with a confidence interval and a careful assessment of study design.

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