Relative Risk and Risk Difference Calculator
Compares how often an outcome occurs in two groups, as a ratio and as a difference.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
risk = with the outcome ÷ group total relative risk = risk₁ ÷ risk₂ risk difference = risk₁ − risk₂
Intervals are large-sample ones: on the log scale for the ratio, and on the plain scale for the difference.
What to watch out for
Report both if you can. A relative risk of 2 sounds the same for a rise from 1 in a million to 2 in a million as from 20% to 40%, and the risk difference shows how far apart those are.
Frequently Asked Questions
What is a worked example?
15 of 100 against 30 of 100 gives a relative risk of 0.5 and a risk difference of -15 points.
What does a relative risk of 1 mean?
The outcome is equally common in both groups. The risk difference would then be 0.