On "weak" and "strong" Population Momentum

Résumé du livre

This paper decomposes total population momentum into two constituent and multiplicative parts called "weak" momentum and "strong" momentum. Weak momentum depends on deviations between a population's observed age distribution and its implied stable age distribution. Strong momentum is a function of deviations between a population's implied stable and stationary age distributions. In general, the factorization of total momentum into the product of weak and strong momentum is a very good approximation. The factorization is exact, however, if the observed age distribution is stable or if initial fertility is already at replacement. We provide numerical illustrations by calculating weak, strong, and total momentum for 176 countries, the world, and its major regions. In short, the paper brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework.