  Three statistical studies, all published between 2004 and 2008 but without
referring to one another, assert a useful equivalence involving the hazard
ratio, a parameter estimated for time to event data by the frequently used
proportional hazards model. Stated generally, when the assumption of
proportional hazards is justified, the hazard ratio is equivalent to the odds
that a randomly chosen person from the group whose hazard is represented in the
ratio's numerator will experience the event of interest before a randomly
chosen person from the group represented by the ratio's denominator.
