Hazard ratio
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Hazard ratio ("HR") is a quantity often used in medical studies to show an a decrease in risk of mortality or harm from using the studied course of treatment. A hazard ratio of 1 signifies no change, while a hazard ratio of 0.5 signifies a 50% reduction in harm.
In other words, the hazard ratio is the risk of the hazard relative to a control group risk of 1.
The hazard ratio is defined formally in two different ways:[1]
- The hazard ratio is the ratio of (chance of an event occurring in the treated group)/(chance of an event occurring in the control group).
- The hazard ratio is the ratio of (risk of outcome in one group)/(risk of outcome in the control group), occurring in a certain interval of time.