Hazard ratios

An overview for nonstatisticians of what hazard ratios are

1. Interpreting Hazard Ratios Terry Shaneyfelt, MD, MPH Associate Professor of Medicine UAB Department of Medicine ebmteacher.com

2. Time-to-event analysis Ratio of hazards Hazard Instantaneous event rate Probability that an individual at time t has an event at that time (assuming event-free survival to time t ) Hazard Ratio Hazard in treatment arm Hazard in control arm HR=

3. HR = 1 (event rates are the same in both arms) HR = 2 (at any time twice as many patients in the treatment group are having an event proportionally to the comparator group) HR = 0.5 (at an time half as many patients in the treatment group are having an event proportionally to the comparator group) Interpreting Hazard Ratios

4. Often interpreted as a relative risk Not technically the same Interpreting Hazard Ratios http://cancerguide.org/scurve_basic.html Lancet 2003;361:1149