Risk difference (RD)

The risk difference is the risk of one group minus the risk of the other, as a proportion or in percentage points. 0 means no difference. The Newcombe interval is safer than the Wald interval for small numbers.

Example: RD = -.009, 95% CI [-.013, -.006]: the risk is 0.9 percentage points lower in the compared group.

Caution: The risk difference describes a difference, it does not show a cause. In a case-control study it cannot be interpreted.