Hazard ratio

"Hazard" refers to the probability that a given event will occur within a defined time period. The hazard ratio (or hazard rate) corresponds to the ratio of the hazard rates of two groups. The hazard ratio (HR) is often used in clinical trials. It indicates the risk ratio between different treatment groups. The risk of one treatment group is put in relation to the risk of a second group. As an example: In a clinical trial, the healing rates of a disease are recorded. While 50 % of the patients in control group II heal, the rate in group I is 40 %. The hazard ratio (HR) is calculated as 0.8. In this example, a ratio of 0.8 means that the patients in group II have a 20 % higher chance of healing than the patients in group I. If the HR is 1, there is no chance of healing. With a HR of 1, there is no difference between the groups.