Population Momentum with Migration

Jonathan Tannen, Princeton University
Thomas J. Espenshade, Princeton University

Population momentum provides an important tool for policy discussions, yet often ignores a critical ingredient to population dynamics: migration. We develop a framework for momentum that incorporates in- and out-migration rates, which allows for a spectrum of momentum values as stationarity is achieved through a combination of fertility and migration rate changes. We apply the framework to Eurostat data, and find that closed-population measures typically underestimate migration-inclusive momentum in these countries. The framework highlights the relationship between momentum and population aging; the policy choice is between high-momentum and older, or low-momentum and younger populations.