In this article, we argue that the conventional measure of population aging, namely the share of people aged 60 and over, essentially accounts for individual aging as captured by in creases in life expectancy and fails to account for population aging. We propose a new measure of population aging that relies on optimal grouping technics initially developed for the analysis of income distributions. The main advantage of this approach is to endogenously define the notion of old age by exploiting the information contained in the entire shape of the age pyramid. We apply this methodology to a group of 12 developed countries. Our results suggest that population aging is considerably weaker than usually claimed. For instance, over the last 50 years, 7 countries out of 12 have not experienced statistically significant aging; one has even experienced a statistically significant rejuvenation. |