Long-range population projections made simple

摘要

Long-range population projections are among the most arresting scientific results that demographers produce. Currently, at least three agencies make projections that extend more than a century into the future: the World Bank (Bos et al. 1994), the United Nations (1998a), and a more recent entrant in the field, the International Institute for Applied Systems Analysis (IIASA) (Lutz 1996). In this analysis, we offer a simpler and potentially more useful means of producing long-range population projections. Our method relies on new developments in mathematical demography by Li and Tuljapurkar (1999). We offer it as a supplement to and a potential replacement for the traditional and comparatively complex approach to long-range population projections. At present analysts use the same method for producing long-term projections as for short-term projections: the cohort-component method that projects each age group according to a specified time path of age-specific fertility and mortality rates. The specification of the pattern and path of age-specific rates is inevitably complicated, resulting in projections that are hard to replicate and difficult to discuss critically. Even when extensive documentation is provided, it is difficult to replicate the calculations without access to proprietary computer software used by the team that prepared the projection.