A new explanation of decreasing failure rate of a mixture of exponentials

It is well known that the mixture of exponential distributions has a,decrea sing failure rate, even though each component in the mixture has a constant failure rate. This result is elegant but sometimes seen as a paradox. This paper shows that the proportion of strong(weak) subpopulation with small(l arge) failure rates in the mixture increases(decreases) as time passes. Bas ed on this fact, a non-Bayes explanation is given for the mixture of expone ntials to have a decreasing failure rate.