The life span of individuals and the life expectancy of the populations they comprise have always been topics of interest to scientists and the lay population. In modern times, forecasts of life span and life expectancy have become particularly important public policy issues because of their...

Differences in methodology and philosophy have led scientists analyzing the same mortality data to arrive at very different conclusions about the behavior of mortality trajectories, the nature of aging, and the future of human longevity. This note describes the authors'views on these issues,...