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Demography

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Map of countries by population
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Map of countries by population

Population growth showing projections for later this century
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Population growth showing projections for later this century

Demography is the scientific study of human population dynamics. It encompasses the study of the size, structure and distribution of populations, and how populations change over time due to births, deaths, migration and ageing. Demographic analysis can relate to whole societies or to groups defined by criteria such as education, nationality, religion and ethnicity. Most countries' demography is regarded as a branch of either economics or sociology. Formal demography limits its object of study to the measurement of populations processes, while the more broad field of population studies also analyze the relationships between economic, social, cultural and biological processes influencing the population.Andrew Hinde Demographic Methods Ch. 1 ISBN 0340718927

The term demographics is often used erroneously for demography, but refers rather to selected population characteristics as used in marketing or opinion research, or the demographic profiles used in such research.

Contents

Data and methods

Demography may rely on the use of large amounts of data, including census returns and vital statistics registers, or incorporate survey data using indirect estimation techniques. The earliest modern census was carried out in the United States in 1790, although the Scandinavian countries had earlier censuses.

In many countries, particularly in the third world, reliable demographic data are still difficult to obtain; census is often equated in the minds of the people with taxation, so the people scatter when a census taker comes around. During the 1980s, for example, the population of Nigeria was widely estimated to be around 101 million people, before it was established to be as little as 89 million people (without adjustment for undercounting) in a census carried out in 1991.

Important concepts

Important concepts in demography include: Note that the crude death rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1000 people can be higher for developed nations than in less-developed countries, despite standards of health being better in developed countries. This is because developed countries have relatively more older people, who are more likely to die in a given year, so that the overall mortality rate can be higher even if the mortality rate at any given age is lower. A more complete picture of mortality is given by a life table which summarises mortality separately at each age. A life table is necessary to give a good estimate of life expectancy.

Basic demographic equation

Suppose that a country (or other entity) contains Populationt persons at time t. What is the size of the population at time [] ?

[Population_ = Population_t + Births_t - Deaths_t + Immigration_t - Emigration_t ]
Net migration from time t to t + 1:

[Net migration_ = Immigration_t - Emigration_t ]
Natural increase from time t to t + 1

[Natural increase_ = Births_t - Deaths_t ]

History

The Natural and Political Observations ... upon the Bills of Mortality (1662) of John Graunt contains a primitive form of life table. Mathematicians, such as Edmond Halley, developed the life table as the basis for life insurance mathematics. Richard Price was credited with the first textbook on life contingencies published in 1771. (ref: “Our Yesterdays: the History of the Actuarial Profession in North America, 1809-1979,” by E.J. (Jack) Moorhead, FSA, ( 1/23/10 – 2/21/04), published by the Society of Actuaries as part of the profession’s centennial celebration in 1989; followed later by Augustus de Morgan, ‘On the Application of Probabilities to Life Contingencies’, (1838). (ref: The History of Insurance, Vol 3, Edited by David Jenkins and Takau Yoneyama (1 85196 527 0): 8 Volume Set: ( 2000) Availability: Japan: Kinokuniya)

At the end of the 18th century, Thomas Malthus concluded that, if unchecked, populations would be subject to exponential growth. He feared that population growth would tend to outstrip growth in food production, leading to ever increasing famine and poverty (see Malthusian catastrophe); he is seen as the intellectual father of ideas of overpopulation and the limits to growth. Later more sophisticated and realistic models were presented by e.g. Benjamin Gompertz and Verhulst.

The demographic transition

Contrary to Malthus' predictions (though in line with his thoughts on moral restraint), natural population growth in most developed countries has diminished to close to zero, without being held in check by famine or lack of resources, as people in developed nations have shown a tendency to have fewer children. The fall in population growth has occurred despite large rises in life expectancy in these countries. This pattern of population growth, with slow (or no) growth in preindustrial societies, followed by fast growth as the society develops and industrialises, followed by slow growth again as it becomes more affluent, is known as the demographic transition.

Similar trends are now becoming visible in ever more developing countries, so that far from spiralling out of control, world population growth is expected to slow markedly in the next century, coming to an eventual standstill. The change is likely to be accompanied by major shifts in the proportion of world population in particular regions. The United Nations Population Division expects the absolute number of infants and toddlers in the world to begin to fall by 2015, and the number of children under 15 by 2025. Demographers at the International Institute for Applied Systems Analysis in Austria expect world population to peak at 9000 million by 2070. Throughout the 21st century, the average age of the population is likely to continue to rise.

See also

References

Further reading

  • Paul R. Ehrlich (1968), The Population Bomb Controversial Neo-Malthusianist pamphlet
  • Leonid A. Gavrilov & Natalia S. Gavrilova (1991), The Biology of Life Span: A Quantitative Approach. New York: Harwood Academic Publisher, ISBN 3718649837
  • Phillip Longman (2004), The Empty Cradle: how falling birth rates threaten global prosperity and what to do about it
  • Ben J. Wattenberg (2004), How the New Demography of Depopulation Will Shape Our Future. Chicago: R. Dee, ISBN 156663606X
  • Andrey Korotayev, Artemy Malkov, & Daria Khaltourina (2006). Introduction to Social Macrodynamics: Compact Macromodels of the World System Growth. Moscow: URSS, ISBN 5484004144 [link]

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