ESSENCE AND CONCEPT OF THE PYRAMID
Karimova Rina, Ableeva Alice, Associate Professor
Bashkir State Agricultural University
Ufa, Bashkortostan, Russia
The term "population pyramid" describes the shape of a diagram
showing the composition, by age and gender, of a nation's population at
the time of a census. It is also called a "population profile." It is a
convenient way to display in visual form the national population
composition, and it is widely used by demographers, vital statisticians,
public health specialists, social policy planners, and the television and
print media when issues of national population are being discussed. The
numbers used to construct the diagram are derived from national census
returns. Because of its pyramid shape, a population pyramid is most aptly
applied to a population with high birth rates and high death rates in infancy
and at all subsequent ages. The term was probably coined with this in
mind, because it evokes an image of small numbers in the upper age
ranges perched on top of much larger numbers of newborn infants and
young children.
The changes in age and gender composition of the population in
many industrial nations in the twentieth century altered the shape of the
population profile, sometimes dramatically. The most obvious changes are
due to a decline in the number of children born, plus reduced death rates at
all ages up to old age. This produces a diagram better described as a
population profile rather than a pyramid. It has a narrower base, a broader
middle, and a blunter apex. Sharp declines in the numbers born at times of
crisis such as wars and severe depressions leave a legacy of a narrowing at
the middle of the profile several decades later.
A population pyramid, also called an age structure diagram, is a
graphical illustration that shows the distribution of various age groups in a
human population (typically that of a country or region of the world),
which ideally forms the shape of a pyramid when the region is healthy. It
is also used in Ecology to determine the overall age distribution of a
population; an indication of the reproductive capabilities and likelihood of
the continuation of a species.
It typically consists of two back-to-back bar graphs, with the
population plotted on the X-axis and age on the Y-axis, one showing the
number of males and one showing females in a particular population in
five-year age groups (also called cohorts). Males are conventionally shown
on the left and females on the right, and they may be measured by raw
number or as a percentage of the total population.
Population pyramids are often viewed as the most effective way to
graphically depict the age and sex distribution of a population, partly
because of the very clear image these pyramids present.
A helpful analogy to facilitate understanding population pyramids is
that just as a builder employs a blueprint for showing a house's structure,
demographers and geographers employ population pyramids as a blueprint
for showing population dynamics.
While all countries' population pyramids differ, four general types
have been identified by the fertility and mortality rates of a country.
Stable pyramid - A population pyramid showing an unchanging
pattern of fertility and mortality.
Stationary pyramid - A population pyramid typical of countries with
low fertility and low mortality, very similar to a constrictive pyramid.
Population pyramids for 4 stages of the demographic transition model
Expansive pyramid - A population pyramid showing a broad base,
indicating a high proportion of children, a rapid rate of population growth,
and a low proportion of older people. This wide base indicates a large
number of children. Steady upwards narrowing shows that more people die
at each higher age band. This type of pyramid indicates a population in
which there is a high birth rate, a high death rate and a short life
expectancy. This is the typical pattern for less economically developed
countries, due to little access to and incentive to use birth control, negative
environmental factors (for example, lack of clean water) and poor access
to health care. Constrictive pyramid - A population pyramid showing
lower numbers or percentages of younger people. The country will have a
graying population which means that people are generally older, as the
country has long life expectancy, a low death rate, but also a low birth rate.
This pyramid has been occurring more frequently, especially when
immigrants are factored out, and is often a typical pattern for a very
developed country, a high over-all education and easy access and incentive
to use birth control, good health care and a low number to no negative
environmental factors.