M. Asadi - Department of Statistics, University of Isfahan- Isfahan, ۸۱۷۴۴. IRAN
S. Goliforushani - Department of Statistics, University of Isfahan- Isfahan, ۸۱۷۴۴. IRAN

In reliability theory and survival analysis there are situations in which the lifetime of a device can be considered as a discrete integer valued random variable such as the number of operating days of the device before the failure. In order to study the ageing behavior of such random variables the concepts of reliability measures, such as failure rate, mean residual lifetime and reversed failure rate, in continuous setting are extended to discrete case. In the present note we introduce a concept of mean past lifetime for non-negative discrete lifetime random variable and study some of its properties.

Reversed hazard rate; Mean residual lifetime; Reliability function.