Statistics and risk
Relative risk
A comparison of outcome risk between two groups, usually expressed as a ratio or percentage change.
What it means
Definition
Relative risk. Relative risk compares one group with another. It is useful for describing the direction and proportion of an effect, but it can exaggerate how important a result feels if the baseline risk is not shown.
What it can tell you
It can show whether a result is being framed as a proportion, percentage or real-world difference.
What it cannot tell you
It cannot show whether the effect is important unless the baseline risk, population and outcome are clear.
Headline trap
Why this matters in headlines
A treatment that halves a very rare risk may still make only a small difference to most individuals.