Some results about the NBUC class of life distributions

NBUC class life distributions are dealt with in this paper. Firstly, a lower bound of the reliability function based upon mean and variance (both assumed finite) is presented. It is shown that the bound effectively improves "known bounds" for NBU life distributions. Secondly, a sufficient condition characterized by the excess lifetime at t > 0 in a renewal process is obtained. In effect, the decreasing in convex ordering of excess lifetime may result in NBUC interarrivals. Finally, we prove that the NBUC class is preserved under the formation of the parallel system. (C) 2000 Elsevier Science B.V. All rights, reserved. MSC: primary 62E10; secondary 60K10.