HR
EVENT
This is the most common measure used in trials. It is defined as the ratio of the two hazard rates
This is easily interpretable under the assumption that the two hazards are proportional, and hence that the chance of experiencing an event in the research arm at a specific time is always HR times that in the control arm, whatever the time. The interpretation under non-proportional hazards is less straightforward and generally requires some definition of average HR.The HR is an ideal summary measure when (a) we are interested in a relative difference measure and (b) the hazards are likely to be approximately proportional. When either condition does not hold, other summary measures may be preferable.