Population pyramid

A population pyramid or ‘population profile’ is detailed diagram referring to the shape of the graphs which demonstrates the composition of a nation’s population in relation to various age groups and sex (cohorts).  It contains two side-to-side placed graphs, one that shows details of the male segment of the population, and the other that shows details of the female segment of the population.  Usually the left hand side shows details of the male segment of the population.  A population profile is usually triangular in shape, the base suggesting a large number of children.  A rapid narrowing of the top bands suggests that people may be dying faster.  The population pyramid provides a lot of other details such as birth rate, death rate, and life-expectancy. The pyramid should be ideally symmetrical to demonstrate similar pattern and numbers between males and females in the nation.
A population pyramid of a nation is of different types depending on several factors such as birth rates, death rates, and situation prevailing in the country.  These include a stationary pyramid, progressive pyramid and regressive pyramid. A stationary pyramid demonstrates a rather constant pattern of fertility and death rate.  A progressive pyramid demonstrates a high turnover of the population (elevated birth and death rates), and a large number of children.  A regressive pyramid on the other hand suggests a dropping birth rate and a low fatality rate.  Some countries may develop a ‘youth bulge’ in their population pyramid (a rise in the youth segment of the population), which may increase the risk for war terrorism and criminal activities to flourish (Answers.Com. 2006).
During a war situation, a nation’s population pyramid may have varying appearances depending on the manner in which it is affected.

The most active segment of the population, that is young men cohort, are usually the most affected during a war.  Due to severe losses, nations often demonstrate a drop in the bar graphs in the adult male cohort group, and excess in the corresponding female segment.  Losses of young and middle-aged men later tend to affect other portions of the population profile.  The birth rate on both the male and the female side would significantly reduce over a period of time.  As this cohort of adult males get older, the excess on the female side and the deficiency in the male side starts climbing.  In the 1965 population pyramid of the United Kingdom, it was seen that the number of middle-aged and elderly men were reduced, compared to the similar female cohort due to losses during the World War (Answers.Com. 2006).
Sometimes, during a war situation, there may be equivalent loss on the adult female cohort side due to frequent deaths arising from childbirth, reduced healthcare facilities, sporadic violence, etc.   Such a population pyramid appears symmetric with a depression of cohorts on the adult male and female side.  This is known as a ‘constrictive pyramid’.   The birth rate and the fertility rates also drop due to a decrease in women and men having a high potential for reproduction.  The population pyramids of the US during the 1940’s show this kind of a pattern as usually the adult population was affected, playing a role in the defense of the nation.  Over a period of time this cohort climbed as it got older (Rosenberg, Matt. 1997).
When a country is affected with a full blown war, all the segments of the population seem to be affected.  All the cohorts tend to get depressed.  The mortality rates increases, whereas the birth rate of the population decreases.  In some countries, the depression may be greater in the young adult segment of the population as they tend to be more involved with the war.   These depressed cohorts tend to carry over with time as the population gets older.  The population pyramid of Japan during the 1940’s shows this kind of a pattern, as civilian populations were also affected (Statistical Handbook of Japan. 2006).
References:
About.Com. “Population Pyramid.” Encyclopedia of Public Health. 2006. Answers.Com. 29 Dec. 2006. http://www.answers.com/topic/population-pyramid
Rosenberg, Matt. “Age-Sex Pyramids.” About Geography. 1997. About.Com. 29 Dec. 2006. http://geography.about.com/library/weekly/aa071497.htm
Statistical Handbook of Japan. “Chapter 2  Population.” Statistics Bureau. 2006. Statistics Bureau of Japan. 29 Dec. 2006. http://www.stat.go.jp/English/data/handbook/c02cont.htm
US Census Bureau. “IDB Population Pyramids.” U.S. Census Bureau Population Division/International Programs Center. 2006. US Census Bureau. 29 Dec. 2006. http://www.census.gov/ipc/www/idbpyr.html