The Power of Pyramids and What They Can Tell Us about the World's Population

The age structure of the world's population in 1970

Tags: aging/life course, demography/population, health/medicine, methodology/statistics, demographic transition, fertility, mortality, total fertility rate, subtitles/CC, 00 to 05 mins
Year: 2015
Length: 4:15
Access: YouTube

Summary: The population pyramid is a visualization of a society's age structure and is so named because of its shape. A thick base at the bottom indicates that the largest share of the population is young, and the pyramid's steep slope, which vanishes to a point, represents the cold fact that the mortality rate increases as people age. In countries around the world, the shape of this pyramid age distribution has been observed to change, a process demographers call a demographic transition. The traditional pyramid shape is common in less industrialized societies, which is an indication that fertility and mortality rates are high and life spans are short. However, with the diffusion of medical advancements, the reach of health care services, and improvments in drinking water and sanitation mortality rates typically drop and life spans increase. And with more children surviving the first decade of life and contraception becoming more widely available, fertility rates typically plummet. The result is that the pyramid-looking age distribution begins to resemble a column. Since each successive bar represents the size of an age cohort, it follows that in a society with a stable fertility rate and a low mortality rate, the bars resist sloping inward until the older age cohorts where mortaility seems to overcome advancements in health.  •   As the above video from The Economist explains, demographic transitions have been observed to happen on a country-by-country basis, but if one pools data from countries around the world, it appears that the age structure of the global population is slowly undergoing one big demographic transition. In 1970, the world's population could be represented as a pyramid, but in 2015 the the pyramid more closely resembles the dome of the U.S. Capitol Building. By 2060, demographers project that the dome-like structure will give way to columns, and it may be difficult to remember why demographers ever called it a population pyramid in the first place.  •   It is important to keep in mind that creating these graphs is more than an exercise in data visualization, and such graphs can be useful tools for policymakers. For instance, whether the age distribution resembles a pyramid or a column has important implications for answering questions about society's tax structure and resource allocations. It is essential to know the number of people who comprise vulnerable populations, such as children and the elderly. Population pyramids and the calculations they represent can also become a catalyst for more philosophical ponderings, such as what it will mean that for the first time in human history the world will have just as many older people as children.

Submitted by: Lester Andrist

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