Population pyramid

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A population pyramid is two back-to-back bar graphs, 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.

A great deal of information about the population broken down by age and sex can be read from a population pyramid, and this can shed light on the extent of its development. There are two basic shapes of population pyramid.

1 Triangular population distribution
2 Types of population pyramid
3 Youth Bulge
4 Uses of population pyramids
5 References
6 See also
7 External links

[edit] Triangular population distribution

This distribution is called after the triangular shape of its population pyramid.

The triangular distribution may also be called a pyramid or exponential distribution. The wide base indicates a large number of children but the rapid narrowing shows that many people die between each age band. The 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 and incentive to use birth control, poor environmental factors (for example: lack of clean water) and little access to health services.

Note that there tends to be more females than males in the older age groups. This is because females tend to have a longer life expectancy.

[edit] Types of population pyramid

While all countries population pyramids differ, three types have been identified by the fertility and mortality rates of a country.

Stationary pyramid - A population pyramid showing an unchanging pattern of fertility and mortality.

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.

Constrictive pyramid - A population pyramid showing lower numbers or percentages of younger people.

[edit] Youth Bulge

The expansive case was described as Youth Bulge by Fuller (1995). Heinsohn (2003) argues that an excess in especially young adult male population predictably leads to social unrest, war and terrorism as the "third and fourth sons" that find no prestigious positions in their existing societies rationalize their impetus to compete by religion or political ideology. Heinsohn claims that most historical periods of unrest and most genocides can be readily explained as a result of a built up youth bulge, including European colonialism, 20th century Fascism, and ongoing conflicts such as that in Darfur and Islamist terrorism.

Afghanistan shows a classical youth bulge

Angola shows the same

China had an extreme youth bulge until the 1960s, since sharply curbed as an effect of the one-child policy

compare the population pyramid of the USA which was bulging until the 1960s and has steadily slimmed since

[edit] Uses of population pyramids

Population pyramids can be used to find the number of economic dependents being supported in a particular population. Economic dependents are defined as those under 15 (children who are in full time education and therefore unable to work) and those over 65 (those who have retired). Of course, in some less economically developed countries children start work well before the age of 15, and in some more economically developed countries it is not usual to start work until 18 or 21, and people may work beyond the official retirement age of 65, but the definition provides an approximation. The government must plan the economy in such a way that the working population can support these dependents.

[edit] References

Gary Fuller, The Demographic Backdrop to Ethnic Conflict: A Geographic Overview, in: The Challenge of Ethnic Conflict to National and International Order in the 1990's, Washington: CIA (RTT 95-10039, Oktober), 151-154.
Gunnar Heinsohn, Söhne und Weltmacht: Terror im Aufstieg und Fall der Nationen, Orell Füssli (2003), ISBN 3280060087 - available online as free download (in german; for information about Heinsohn´s theory in english, see the two short papers linked below)

Generally a population pyramid which displays a population percentage of 'ages 1-14 over 30% and ages 75 and above under 6% is consitered a 'young population' (generally occurring in developing countries, with a high agricultural workforce). A population pyramid which displays a population percentage of 'ages 1-14 under 30% and ages 75 and above over 6% is consitered an 'aging population' (that of which generally occurs in developed countries with adequate health services, e.g. Australia). A country which displays all or none of these characteristics is consitered niether.