This distribution is named for the pyramidal shape of its graph.

A population pyramid, also called age-sex pyramid and age structure diagram, is a graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which normally forms the shape of a pyramid. In Biology a population is the collection of inter-breeding organisms of a particular Species; in Sociology A pyramid is a Building where the upper surfaces are triangular and converge on one point 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). In Statistics and Demography, a cohort is a group of subjects &mdash most often humans from a given population &mdash defined by experiencing an event (typically 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. In Mathematics, a percentage is a way of expressing a number as a Fraction of 100 ( per cent meaning "per hundred"

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 development and other aspects of the population. A population pyramid also tells the council how many people of each age range live in the area. There tends to be more females than males in the older age groups, due to females' longer life expectancy.

## Types of population pyramid

Population pyramids for 4 stages of the demographic transition model

While all countries population pyramids differ, three types have been identified by the fertility and mortality rates of a country. The Demographic transition model (DTM is a model used to explain the process of shift from high Birth rates and high Death rates to low birth rates and low death rates

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. This wide base indicates a large number of children. A 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. Crude birth rate is the natality or Childbirths per 1000 people per year Mortality rate is a measure of the number of Deaths (in general or due to a specific cause in some population scaled to the size of that population per unit time Life expectancy is the average number of years of life remaining at a given age 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. Birth control, sometimes synonymous with contraception, is a regimen of one or more actions devices or Medications followed in order to deliberately prevent

Constrictive pyramid - A population pyramid showing lower numbers or percentages of younger people. The country will have a greying population which means that people are generally older.

## Youth bulge

Median age by country. A baby boom is any period of greatly increased birth rate during a certain period and usually within certain geographical bounds and when the birth rate exceeds 2% of the population A population pyramid, also called age-sex pyramid and age structure diagram, is a graphical illustration that shows the distribution of various age groups in a A youth bulge is evident for Africa, and to a lesser extent for South and Southeast Asia and Central America. The population of Africa has grown exponentially over the past century and consequently shows a large Youth bulge, further reinforced by a low

The expansive case was described as youth bulge by Gary Fuller (1995). Gunnar 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. Gunnar Heinsohn (born 1943 in the German-occupied city of Gotenhafen (today Gdynia, Poland) is a German sociologist. War is an international relations Dispute, characterized by organized Violence between National Military units Terrorism is the systematic use of terror especially as a means of coercion Heinsohn claims that most historical periods of social unrest lacking external triggers (such as rapid climatic changes or other catastrophic changes of the environment) 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 terrorism. Genocide is the deliberate and systematic destruction in whole or in part of an ethnic racial religious or national group The first European colonization wave took place from the early 15th century until the early 19th century and primarily involved the European colonization of the Americas, though Fascism is a totalitarian nationalist and corporatist ideology The War in Darfur is a military conflict in the Darfur region of western Sudan. Terrorism is the systematic use of terror especially as a means of coercion

One problem with this line of reasoning is that under conditions prevailing before the introduction of modern medicine, death rates were much higher than they are now and almost all societies had youth bulges, even when their population growth rate was negligible. However, they certainly did not experience such youth bulge as prevails today in some parts of the world or as prevailed in twentieth century Germany or in Africa and the Middle East nowadays. It's not just that most periods of unrest occurred in societies with youth bulges, but that some of the pre-modern periods of any sort existed in societies with such bulges as well. Nevertheless since the improvement of medicine and its introduction the element of youth bulge has become far more salient than before. Therefore perhaps it cannot explain massacres throughout human history, but it can serve as rather plausible theory to explain the terror, social unrest, and uprisings of today.

Another problem is that it ignores the social consequences of poverty, corruption and mass unemployment among young males in developing countries, where most of the world's current population growth is occurring. The "youth bulge" is not an accurate predictor of social unrest, war and terrorism, because they are the product of far more complicated and interrelated set of factors of which demographics only plays a part. Yet even when there are other factors and circumstance to enable mass unrest, a youth bulge is likely to be one of them.

Youth bulge theory represents one of the most recently developed theories of war and social unrest and has become highly influential on U. War is an international relations Dispute, characterized by organized Violence between National Military units S. foreign policy as two major U. S. proponents of the theory, U. S. political scientist Jack Goldstone[1] and U. Jack A Goldstone is an American Sociologist and Political scientist, specializing in studies of Social movements, Revolutions and International S. political scientist Gary Fuller,[2] have acted as consultants to the U. S. government.

## 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 the option of being retired). Of course, in some less developed countries children start work well before the age of 15, and in some developed countries it is common to not start work until 18 or 21, and people may work beyond the age of 65, or retire early. Therefore, the definition provides an approximation. In many countries, the government plans the economy in such a way that the working population can support these dependents. Age pyramid has similar uses to population pyramid.

Population pyramids can be used to observe the natural increase, birth, and death rate.

## References

1. ^ Goldstone, Jack A. : "Revolution and Rebellion in the Early Modern World", Berkeley 1991
2. ^ Fuller, Gary: "The Demographic Backdrop to Ethnic Conflict: A Geographic Overview", in: CIA (Ed. ): "The Challenge of Ethnic Conflict to National and International Order in the 1990s", Washington 1995, 151-154
• Gary Fuller, "The Youth Crisis in Middle Eastern Society" (2004) download
• Gary Fuller, The Demographic Backdrop to Ethnic Conflict: A Geographic Overview, was born in 1989 and was produced by Edward Gewin: The Challenge of Ethnic Conflict to National and International Order in the 1990s, Washington: CIA (RTT 95-10039, October), 151-154.
• Gunnar Heinsohn, Söhne und Weltmacht: Terror im Aufstieg und Fall der Nationen, Orell Füssli (2003), ISBN 3-280-06008-7 - 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 that displays a population percentage of ages 1-14 over 30% and ages 75 and above under 6% is considered a "young population" (generally occurring in developing countries, with a high agricultural workforce). A population pyramid that displays a population percentage of ages 1-14 under 30% and ages 75 and above over 6% is considered an "aging population" (that of which generally occurs in developed countries with adequate health services, e. g. Australia). A country that displays all or none of these characteristics is considered neither.