Some preservation results of NBUC aging property with applications

This paper develops a new characterization of NBUC aging property, and investigates its preservation properties both under monotonic anti-star-shaped transformations and under the non-homogeneous Poisson shock models.     

An aging notion derived from the increasing convex ordering: the NBUCA class

In this paper, comparison between the life distribution of a new unit with that of the remaining life or a used unit in the increasing convex order leads us to introduce a new class of life distributions which we call new better than used in increasing convex average order and denote by NBUCA. This class includes as subclasses the new better than used, NBU and the new better than used in increasing convex ordering, NBUC. Several properties of this class are presented, including the preservation under convolution, random maxima, mixing and formation of coherent structures. Stochastic comparisons of the excess lifetime at different times of a renewal process when the interarrival times belong to the NBUCA class are established. We provide also some applications of Poisson shock models. Finally testing exponentially against NBUCA is presented.     

A Bayesian positive dependence of survival times based on the multivariate arrangement increasing property

We introduce a new notion of positive dependence of survival times of system components using the multivariate arrangement increasing property. Following the spirit of Barlow and Mendel (J. Amer. Statist. Assoc. 87, 1116–1122), who introduced a new univariate aging notion relative to exchangeable populations of components, we characterize a multivariate positive dependence with respect to exchangeable multicomponent systems. Closure properties of such a class of distributions under some reliability operations are discussed. For an infinite population of systems our definition of multivariate positive dependence can be considered in the frequentist’s paradigm as multivariate totally positive of order 2 with an independence condition. de Finetti(-type) representations for a particular class of survival functions are also given.