Global Population Pyramids

The Lancet has just published a recent set of papers from the Global Burden of Disease Study. As it notes: "The Global Burden of Disease Study (GBD) is the most comprehensive worldwide observational epidemiological study to date. It describes mortality and morbidity from major diseases, injuries and risk factors to health at global, national and regional levels. Examining trends from 1990 to the present and making comparisons across populations enables understanding of the changing health challenges facing people across the world in the 21st century." 

Interested readers will find lots to chew on in these papers. Here, I'll stick to a figure showing "global population pyramids" from the article "Population and fertility by age and sex for 195 countries andterritories, 1950–2017: a systematic analysis for the Global Burden of Disease Study 2017," authored by the GBD 2017 Population and Fertility Collaborators (Lancet, published November 10, 2018; 392: 10159, pp. 1995–2051). 

The four panels show four years: 1950, 1975, 2000, and 2017. The red bars show size of female population at different age groups, from younger ages at the bottom to older ages at the top; the yellow bars do the same for men. Horizontal lines show the average and median age for men and women in each year.

A few thoughts:

1) These population pyramids are especially useful for looking at the evolution of the age distribution. "In 1950, the global mean age of a person was 27 years, decreasing to 26 years in 1975, then increasing to 29 years in 2000 and 32 years in 2017.

2) The bulge in the working age population in 2000 and 2017, as opposed to the earlier years, is apparent. " Demographic change has economic consequences, and the proportion of the population that is of working age (15–64 years) decreased from 60% in 1950 to 57% in 1975, then increased to 63% in 2000 and 65% in 2017."

3) Over time, the population pyramids has become relatively broader at the bottom; that is, they do not taper as quickly as one moves to older aged. That pattern tells you that the elderly are a rising share of the population. It also suggests that as today's younger generations age, and their number rise up through the global population pyramid, the share of the elderly in the world population will rise substantially.

4) The increasing area of the pyramids shows the rise in global population since 1950. Less clear to the naked eye is that the rate of growth in the world population has shifted from being exponential to being linear. 

"From 1950 to 1980, the global population increased exponentially at an annualised rate of 1.9% ... . From 1981 to 2017, however, the pace of the global population increase has been largely linear, increasing by 83.6 million people per year. ... Growth of the global population increased in the 1950s and reached 2.0% per year in 1964, then slowly decreased to 1.1% in 2017." 

A version of this article first appeared on Conversable Economist.