Relative Risk Calculator
Compute relative risk RR = [a/(a+b)]/[c/(c+d)] and its 95% confidence interval from a 2×2 table.
Input Data
Exposed with outcome.
Exposed without outcome.
Unexposed with outcome.
Unexposed without outcome.
Results
1.3333
0.8373
2.1231
At a glance:RR = [a/(a+b)] / [c/(c+d)]; 95% CI via ln(RR) ± 1.96·√(1/a − 1/(a+b) + 1/c − 1/(c+d)).
Formula
RR = (a/(a+b)) / (c/(c+d))
$$RR = \frac{a/(a+b)}{c/(c+d)}$$How to Use
- Fill in the four cell counts a, b, c, d of the 2×2 table.
- The calculator outputs the RR.
- Read the 95% confidence interval (lower/upper).
- If the interval excludes 1, the risk difference is significant.
FAQ
Which is better, RR or OR?
Prospective cohort studies can compute RR directly and it is more intuitive ('how many times the risk'). Case-control studies select cases/controls first, so only OR can be estimated. They are close when the outcome is rare.
What does RR = 1 mean?
RR=1 means exposure and outcome are unrelated; RR>1 means exposure increases risk; RR<1 means exposure reduces risk (protective).
References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.