pyramids: Powerful predictors of the future
Russia, with the largest
territory in the world, has roughly the same total population as Nigeria, a
country 1/16 its size. But this similarity won't last long. One of the
populations is rapidly growing, while the other is slowly declining. What can
this tell us about the two countries?
are some of the most important data social scientists and policy experts have
to work with. But understanding a country's situation and making accurate
predictions requires knowing not just the total size of the population but its internal
characteristics, such as age and gender distribution. So, how can we keep track
of all that data in a way that makes it easy to comprehend?
Complex data is more
easily interpreted through visualisation and one of the ways that demographers represent
the internal distribution of a population is the population pyramid. Here, the
data is divided by gender with females on one side and males on the other. The
population numbers are shown for each five-year age interval, starting from 0-4
and continuing up to 100 and up. These intervals are grouped together into
pre-reproductive (0-14), reproductive (15-44), and post-reproductive years (45
Such a population
pyramid can be a powerful predictor of future population trends. For example, Rwanda's population pyramid shows it to be a
fast-growing country, with most of the population being in the youngest age
groups at the bottom of the pyramid. The number will grow rapidly in the coming
years. As today's children reach their reproductive years and have children of
their own, the total population is almost certain to double within the next few
For our second example, let's look
at Canada where most of the population is clustered around the middle of the
graph. Because there are fewer people in the pre-reproductive age groups than
there are in the reproductive ones, the population will grow more slowly, as
the number of people reaching their reproductive years’ decreases.
Finally, let's look at Japan. Because
the majority of its population is in its post-reproductive years and the number
of people is smaller at each younger interval, this means that at current rates
of reproduction the population will begin to decline as fewer and fewer people
reach reproductive age. Comparing these three population pyramids side by side shows
us three different stages in a demographic transition as a country moves from a
pre-industrial society to one with an industrial or post-industrial economy.
Countries that have only recently
begun the process of industrialisation typically see an increase in life
expectancy and a fall in child mortality rates as a result of improvements in
medicine, sanitation and food supply. Birth rates remain constant, leading to a
population boom. Developing countries that are farther along in the
industrialisation process begin to see a fall in birth rates due to factors
such as increased education and opportunities for women outside of
child-rearing and a move from rural to urban living that makes having large
families less economically advantageous. Finally, countries in advanced stages
of industrialisation reach a point where both birth and death rates are low and
the population remains stable or even begins to decline.
Now, let's consider the projected
population pyramids for the same three countries in 2050. What do these tell us
about the expected changes in each country's population and what kinds of
factors can alter the shape of these future pyramids? A population pyramid can
be useful not only as a predictor of a country's future but as a record of its
past. Russia's population pyramid still bears the scars of World War II, which
explains both the fewer numbers of elderly men compared to elderly women and
the relatively sudden population increase as soldiers
returned from the war and normal life resumed.
China's population pyramid reflects
the establishment of the one-child policy 35 years before, which prevented a
population boom such as that of Rwanda. However, it also led to sex-selective
abortions, resulting in more male children than female children.
Finally, the pyramid for the United
States shows the baby boom that followed World War
II. The population pyramids tell us far more about a country than just a set of
numbers by showing both where it's been and where it's headed within a single
image. And in today's increasingly interconnected world, facing issues such as
food shortages, ecological threats, and economic disparities, it is
increasingly important for both scientists and policymakers to have a rich and
complex understanding of populations and the factors affecting them.
Source: TED Ed. Written by Kim Preshoff.