Monday, November 12, 2018

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 26·6 years, decreasing to 26·0 years in 1975, then increasing to 29·0 years in 2000 and 32·1 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 59·9% in 1950 to 57·1% in 1975, then increased to 62·9% in 2000 and 65·3% 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." 
5) Although geographic breakdowns aren't shown in this figure, the regional patterns of population growth have also differed substantially. 
"In 1950, the high-income, central Europe, eastern Europe, and central Asia GBD super-regions accounted for 35·2% of the global population but, in 2017, the populations of these countries accounted for 19·5% of the global population. Large increases occurred in the proportion of the world’s population living in south Asia, sub-Saharan Africa, Latin America and the Caribbean, and north Africa and the Middle East. ...  Growth of the population in north Africa and the Middle East increased until the 1970s, and it has remained quite high, at 1·7% in 2017. Population growth rates in sub-Saharan Africa increased from 1950 to 1985, decreased during 1985–1993, increased again until 1997, and then plateaued; at 2·7% in 2017, population growth rates were almost the highest rates ever recorded in this region. The most substantial changes to population growth rates were in the southeast Asia, east Asia, and Oceania super-region, where the population growth rate decreased from 2·5% in 1963 to 0·7% in 2017. ... In central Europe, eastern Europe, and central Asia, the population growth rate dropped rapidly after 1987 and was negative from 1993 to 2008. Growth rates in the high-income super-region have changed the least, starting at 1·2% in 1950 and reaching 0·4% in 2017."