Hazard Ratio (HR)The hazard ratio is the ratio of (chance of an event occurring in the treatment arm)/(chance of an event occurring in the control arm). The HR has also been defined as, the ratio of (risk of outcome in one group)/(risk of outcome in another group), occurring at a given interval of time
A hazard ratio of 1 means lack of association, a hazard ratio greater than 1 suggests an increased risk (i.e disease progression or death ), and a hazard ratio below 1 suggests a smaller risk.