Health systems have multiple goals, but the fundamental reason they exist is to improve health. Yet health systems with very similar levels of health expenditure per capita show wide variations in population health outcomes. Part of the difference can be explained by variation in non-health system factors, such as the level of education of the population. But part can also be explained by the fact that some systems devote resources to expensive interventions with small effects on population health, while at the same time low cost interventions with potentially greater benefits are not fully implemented.