In a recent post, we drew attention to the importance of the support ratio (defined as the ratio of people aged 20-64 to those over 64, or under 20) in determining living standards (per capita natural wealth).
Gerland and colleagues have recently reported on the latest UN report “World Population Projections”. Projected population growth rates and support ratios have been modelled for the remainder of the century by continent. Their model represents an advance on previous deterministic models, since it used Bayesian methodology to sample from distributions for model parameters, such as fertility rates. The resulting probabilistic sensitivity analysis yielded narrower credible limits than previous crude models. The model also admits external evidence by eliciting prior distributions for unobserved events, such as future life expectancy.
According to the model projections, Africa’s population will be similar to that of Asia by the end of the century, and there is a probability of about 70% that it will exceed it. However, the support ratio for Africa will be much higher (over 5) than for Asia (under 3) or current high-income countries (under 2). Africa will be the new ‘superpower’.
Of course, demography is an inherently uncertain business. Current evidence suggests that fertility rates in Africa are declining at a considerably slower rate than they did in Asia and South America at a corresponding stage of development (see our previous blog). If, however, the rate of decline accelerates soon, then the world’s population will be considerably smaller than projected above.
Our CLAHRC is collaborating with the African Population and Health Research Center (APHRC) in Nairobi to test the hypothesis that early signs of an increase in the rate of decrease are imminent. One thing is reasonably clear, major catastrophe (such as nuclear war) aside, uncertainty about the world’s future population turns mainly on uncertainties about Africa’s population.
— Richard Lilford, CLAHRC WM Director
- Gerland P, Raftery AE, Ševčíková H, Li N, Gu D, Spoorenberg T, Alkema L, Fosdick BK, Chunn J, Lalic N, Bay G, Buettner T, Heilig GK, Wilmoth J. World population stabilization unlikely this century. Science. 2014; 346(6206): 234-7.