  Some years ago, Snapinn and Jiang[1] considered the interpretation and
pitfalls of absolute versus relative treatment effect measures in analyses of
time-to-event outcomes. Through specific examples and analytical considerations
based solely on the exponential and the Weibull distributions they reach two
conclusions: 1) that the commonly used criteria for clinical effectiveness, the
ARR (Absolute Risk Reduction) and the median (survival time) difference (MD)
directly contradict each other and 2) cost-effectiveness depends only the
hazard ratio(HR) and the shape parameter (in the Weibull case) but not the
overall baseline risk of the population. Though provocative, the first
conclusion does not apply to either the two special cases considered or even
more generally, while the second conclusion is strictly correct only for the
exponential case. Therefore, the implication inferred by the authors i.e. all
measures of absolute treatment effect are of little value compared with the
relative measure of the hazard ratio, is not of general validity and hence both
absolute and relative measures should continue to be used when appraising
clinical evidence.
