The fact that the relationship between income and health is concave indicates that a transfer of income from the rich to the poor would increase the average health of a society. However, this policy prescription will have this effect only if the relationship between income and health is causal – i.e. if higher income causes longer life expectancy (see below). If the relationship is driven by other factors, if it is spurious, or if it is in fact health that leads to higher income, then this policy outcome will no longer be true.