Consider an item which can be repaired N times, where each repair is general in the sense of Kijima. Suppose that the item continuously yields a benefit whose rate at any time t depends only on the virtual age of the item at time t. We find conditions, on the benefit rate function and on some underlying distribution functions, under which the value (that is, the total benefit) of the item stochastically increases as a function of the inter-failure random times. We also consider an item on which N preventive maintenance actions can be performed, where each such action modifies the virtual age of the item. Again, we assume that the benefit rate of the item at time t depends only on its virtual age at that time, and we find conditions under which the value of the item stochastically increases as a function of the inter-maintenance times.
