Mortality traps and the dynamics of health transitions.

An examination of life expectancy in 1963 reveals twin peaks in the empirical distribution across countries: one group of countries clustered around a life expectancy of 40 years and a second group clustered around a life expectancy of 65 years. By 2003, the mode of each cluster had moved up by approximately 10 years. Although the two groups are similar in that within each of them, there is progress toward higher life expectancy, a number of countries appear to have made the jump from the high-mortality cluster to the low-mortality cluster. We reject the hypothesis that these changes reflect a simple convergence process. The data instead suggest continuous advances among many countries within clusters, with advances in life expectancy in some nations resulting in a jump from one cluster to the other.