Relative Risk Calculator
Enter counts
Use the number of people with and without the event in each group.
Event
No event
Total
Exposed
or intervention
300
Unexposed
or control
300
Confidence level
95%
Event interpretation
Relative risk
0.667
95% CI: 0.539 to 0.825
Lower risk
The exposed/intervention group has about 33.3% lower risk of the event than the unexposed/control group.
Risk: exposed
30.0%
90 of 300
Risk: unexposed
45.0%
135 of 300
Risk difference
−15.0 pp
Exposed − unexposed
Relative change
−33.3%
(RR − 1) × 100
Wald z / p
−3.724
p = 0.000196
NNT / NNH
7
If exposure is an intervention
Event risk comparison
Relative risk with confidence interval
How this is calculated
The confidence interval is the conventional log (Wald) interval for a risk ratio. It is most appropriate when the data arise from independent prospective groups and cell counts are not sparse. Relative risk is generally not directly estimable from ordinary case-control sampling. The optional 0.5 zero-cell correction is an approximation for sensitivity checking, not an exact small-sample interval.
