Statistics and risk
Hazard ratio
A time-to-event measure comparing the rate at which an outcome occurs between groups over follow-up.
What it means
Definition
Hazard ratio. A hazard ratio is common in survival and long-term follow-up studies. It compares the instantaneous event rate between groups, not simply the percentage of people affected by the end of the study.
What it can tell you
It can help clarify what sort of evidence or claim is being discussed.
What it cannot tell you
It cannot, by itself, prove that the headline is accurate or clinically important.
Headline trap
Why this matters in headlines
A hazard ratio in a cancer trial should be interpreted alongside absolute survival, follow-up time and confidence intervals.