The immediate effect of discovering a way to cure cancer would be a reduction in the number of deaths in the United States by the number of people now dying from that cause. Within a short time, however, deaths from other causes would increase, and the net long-term effect would be relatively small. A parameter is derived that measures how much the expectation of life is increased by a marginal reduction in any cause of death. That parameter is additive in the several causes and has other advantages, though it does not avoid the assumption of independence.