In Discussion paper No. 1283 William H Dow, Jessica Holmes, Tomas Philipson and Research Fellow Xavier Sala-i-Martin provide a theoretical and empirical investigation of the positive complementarities between disease-specific policies introduced by competing risks of mortality. The main point of this paper is that the incentive to invest in prevention against one cause of death depends positively on the level of survival from other causes. This means that a specific public health intervention has benefits other than the direct medical reduction in mortality; it affects the incentives to fight other diseases, so the overall reduction in mortality will, in general, be larger than that predicted by the direct medical effects.

The authors get some insights from reliability theory, which is used by engineers to evaluate how the lifetimes of different components of a machine affect the survival and durability of the whole device. With regard to human life extension, there may be important spillovers across components as the reduction in the probability of death from one `failed component' affects the incentives to invest in the prevention of alternative life-threatening `component failures' or diseases. They discuss evidence of these cross-disease effects by using data on neonatal tetanus vaccination through the Expanded Programme on Immunization of the World Health Organization.