Demography

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Map of countries by population

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.^[1]

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.

[edit] Data and methods

Demographers 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 developing countries, reliable demographic data is 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.

[edit] Important concepts

Important concepts in demography include-:

• The crude birth rate, the annual number of live births per thousand people.
• The general fertility rate, the annual number of live births per 1000 women of childbearing age (often taken to be from 15 to 49 years old, but sometimes from 15 to 44).
• age-specific fertility rates, the annual number of live births per 1000 women in particular age groups (usually age 15-19, 20-24 etc.)
• The crude death rate, the annual number of deaths per 1000 people.
• The infant mortality rate, the annual number of deaths of children less than 1 year old per thousand live births.
• The expectation of life (or life expectancy), the number of years which an individual at a given age can expect to live at present mortality levels.
• The total fertility rate, the number of live births per woman completing her reproductive life, if her childbearing at each age reflected current age-specific fertility rates.
• The gross reproduction rate, the number of daughters who would be born to a woman completing her reproductive life at current age-specific fertility rates.
• The net reproduction ratio is the expected number of daughters, per newborn prospective mother, who may or may not survive to and through the ages of childbearing.

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.

The fertility rates can also give a misleading impression that a population is growing faster than it in fact is, because measurement of fertility rates only involves the reproductive rate of women, and does not adjust for the sex ratio. For example, if a population has a total fertility rate of 4.0 but the sex ratio is 66/34 (twice as many men as women), this population is actually growing at a slower natural increase rate than would a population having a fertility rate of 3.0 and a sex ratio of 50/50. This distortion is greatest in India and Myanmar, and is present in Chinese demographics as well.

[edit] Basic demographic equation

Suppose that a country (or other entity) contains Population_t persons at time t. What is the size of the population at time t + 1 ?

Population_{t + 1} = Population_t + Naturalincrease_t + Netmigration_t

Natural increase from time t to t + 1:

Naturalincrease_t = Births_t − Deaths_t

Net migration from time t to t + 1:

Netmigration_t = Immigration_t − Emigration_t

[edit] 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.

[edit] The demographic transition

World population from 500CE to 2150, based on UN 2004 projections (red, orange, green) and US Census Bureau historical estimates (black). Only the section in blue is from reliable counts, not estimates or projections.

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 or even declining. 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. The figure in this section shows the latest (2004) UN projections of world population out to the year 2150 (red = high, orange = medium, green = low). The UN "medium" projection shows world population reaching an approximate equilibrium at 9 billion by 2075. Working independently, demographers at the International Institute for Applied Systems Analysis in Austria expect world population to peak at 9 billion by 2070. Throughout the 21st century, the average age of the population is likely to continue to rise.

[edit] See also

• Biodemography of human longevity
• Gompertz-Makeham law of mortality
• Important publications in demography
• Medieval demography
• Plant demography
• Population geography
• Reproductive health
• Sociology
• Social surveys: General Social Survey, ALLBUS, GSOEP, PSID, European Social Survey, World Values Survey

[edit] References

1. ^ Andrew Hinde Demographic Methods Ch. 1 ISBN 0-340-71892-7

[edit] 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 3-7186-4983-7
• 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 1-56663-606-X
• Andrey Korotayev, Artemy Malkov, & Daria Khaltourina (2006). Introduction to Social Macrodynamics: Compact Macromodels of the World System Growth. Moscow: URSS, ISBN 5-484-00414-4 [1]

[edit] External links

• International Institute for Applied Systems Analysis (IIASA) IIASA is a non-governmental research institution studying sustainability and the human dimensions of global change for the scientific community, policy makers and the public.
• Centre for Population Studies, London School of Hygiene & Tropical Medicine, the UK's largest research centre focusing on demography and reproductive health.
• Committee for International Cooperation in National Research in Demographyaims at developing cooperation amongst national population research centres, and encouraging new research
• Max Planck Institute for Demographic Research The MPIDR began its activities in October 1996, but it has already become one of the largest non-governmental research bodies in demography in the world.
• Population Studies a journal of demography.
• Online Journal Demographic Research A free, open access, expedited, peer-reviewed journal of the population sciences published regularly on the web.
• Historicalstatistics.org Links to historical demographic and economic statistics
• The Population Reference Bureau has two introduction to demography texts on line. "Population Handbook" and "Population: A Lively Introduction".
• Population Studies Center at the University of Michigan one of the oldest and most active demography research centers in the United States.
• Population Studies Center at the University of Pennsylvania since 1962 turning life into statistics.
• Department of Demography, University of California, Berkeley
• Département de démographie, Université de Montréal
• Institute National d'Etudes Démographiques French National Institute
• Center for Demography and Ecology at the University of Wisconsin,Madison one of the leading centers of demographic research in the world.
• CensusScope U.S. Social Demography site containing data, charts, and color coded maps for country, state, county, and metropolitan geographies.
• Brief review of world basic demographic trends Review of world changes in population and growth, infant mortality, fertility and age distributions.
• Brief review of world socio-demographic trends Review of world changes in urbanization, education and ethnolinguistic fractionalization.
• PopulationData.net Informations and maps about populations around the world. French, with Babelfish translation.
• Phillip Longman, New Statesman, 31 May 2004, "Everywhere, even in Africa, the world is running out of children"
• Ed Stephan's Timeline of Demography Highlights in the history of demography from 3800 BC to 2000 AD.
• United Nations Population Division Homepage(e.g. Population Estimates and Projections Data Online)
• UN 2004 population projections
• NationMasterNationMaster is a vast compilation of data from such sources as the CIA World Factbook, UN, and OECD