Relative Risk Calculator
Calculate relative risk from exposed and control event counts.
Relative risk formula
RR = [a/(a+b)] / [c/(c+d)]. A risk ratio of 1 means equal risk between the two groups.
How to Interpret Relative Risk
Relative risk compares the probability of an outcome in one group with the probability in another. A value of 1 means equal risk, values above 1 indicate higher risk in the first group, and values below 1 indicate lower risk.
Relative Risk Example
If 20 of 100 exposed participants experience an outcome and 10 of 100 unexposed participants do, the risks are 0.20 and 0.10, giving a relative risk of 2.0.
Important Considerations
Relative risk is easiest to interpret when group sizes and event counts are known. Confidence intervals and study design should also be considered before drawing conclusions.
Frequently Asked Questions
Is relative risk the same as odds ratio?
No. Relative risk compares probabilities, while odds ratio compares odds.
Can relative risk be zero?
Yes, when the event risk in the first group is zero and the comparison risk is positive.
What does RR below 1 mean?
It indicates lower risk in the first group relative to the comparison group.
Methodology, Assumptions and Interpretation
Relative risk compares event probability in an exposed group with that in a comparison group: RR = risk₁ / risk₀. It is not the same as an odds ratio, and confidence intervals are needed to describe sampling uncertainty around the point estimate.