Asymptotic behavior of mixture failure rates

Mixtures of increasing failure rate distributions (IFR) can decrease at least in some intervals of time. Usually this property is observed asymptotically as time tends to infinity , which is due to the fact that a mixture failure rate is ‘bent down’, as the weakest populations are dying out first. We consider a survival model, generalizing a very well known in reliability and survival analysis additive hazards, proportional hazards and accelerated life models. We obtain new explicit asymptotic relations for a general setting and study specific cases. Under reasonable assumptions we prove that asymptotic behavior of the mixture failure rate depends only on the behavior of the mixing distri-bution in the neighborhood of the left end point of its support and not on the whole mixing distribution.

On asymptotic failure rates in bivariate frailty competing risks models

A bivariate competing risks problem is considered for a rather general class of survival models. The lifetime distribution of each component is indexed by a frailty parameter. Under the assumption of conditional independence of components the correlated frailty model is considered. The explicit asymptotic formula for the mixture failure rate of a system is derived. It is proved that asymptotically the remaining lifetimes of components tend to be independent in the defined sense. Some simple examples are discussed.

On mixture failure rate ordering

Mixtures of increasing failure rate distributions (IFR) can decrease at least in some intervals of time. Usually this property can be observed asymptotically as time tends to infinity. This is due to the fact that the mixture failure rate is ‘bent down’ compared with the corresponding unconditional expectation of the baseline failure rate, which was proved previously for some specific cases. We generalize this result and discuss the “weakest populations are dying first” property, which leads to the change in the failure rate shape. We also consider the problem of mixture failure rate ordering for the ordered mixing distributions. Two types of stochastic ordering are analyzed: ordering in the likelihood ratio sense and ordering in variances when the means are equal.

Failure rates modelling for heterogenous populations

Mixture of distributions, decreasing failure rate, increasing failure rate, proportional hazards model, accelerated life model, asymptotic behavior of mixture failure rateMagdeburg, Univ., Fak. für Mathematik, Diss., 2006von Veronica Esaulov

On asymptotic failure rates in bivariate frailty competing risks models

A bivariate competing risks problem is considered for a rather general class of survival models. The lifetime distribution of each component is indexed by a frailty parameter. Under the assumption of conditional independence of components the correlated frailty model is considered. The explicit asymptotic formula for the mixture failure rate of a system is derived. It is proved that asymptotically, as t-->[infinity], the remaining lifetimes of components tend to be independent in the defined sense. Some simple examples are discussed.

1.2 Conditional characteristics and simplest models........ 11

zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.), genehmigt durc