Mean residual life order of convolutions of heterogeneous exponential random variables

  • Authors:
  • Peng Zhao;N. Balakrishnan

  • Affiliations:
  • School of Mathematics and Statistics, Lanzhou University, Lanzhou 730000, China;Department of Mathematics and Statistics, McMaster University, Hamilton, Ontario, Canada L8S 4K1

  • Venue:
  • Journal of Multivariate Analysis
  • Year:
  • 2009

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Abstract

In this paper, we study convolutions of heterogeneous exponential random variables with respect to the mean residual life order. By introducing a new partial order (reciprocal majorization order), we prove that this order between two parameter vectors implies the mean residual life order between convolutions of two heterogeneous exponential samples. For the 2-dimensional case, it is shown that there exists a stronger equivalence. We discuss, in particular, the case when one convolution involves identically distributed variables, and show in this case that the mean residual life order is actually associated with the harmonic mean of parameters. Finally, we derive the ''best gamma bounds'' for the mean residual life function of any convolution of exponential distributions under this framework.