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{{Merge |Demographics |discuss=Talk:Demographics#Merge discussion |date=July 2012}}
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{{sociology}}
{{about|the term|the journal|Demography (journal)}}
'''Demography''' is the [[statistical study]] of human [[populations]]. It can be a very general science that can be applied to any kind of dynamic living population, i.e., one that changes over time or space (see [[population dynamics]]). It encompasses the study of the size, structure, and distribution of these populations, and spatial and/or temporal changes in them in response to [[birth]], [[Migration (human)|migration]], [[aging]and [[death]].


“Demo” means “the people” and “graphy” means “measurement”. <ref>See [http://www.merriam-webster.com/dictionary/demography for etymology (origins) of demography].</ref>
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[[Demographic analysis]] can be applied to whole societies or to groups defined by criteria such as [[education]], [[nationality]], [[religion]] and [[ethnicity]]. Institutionally, demography is usually considered a field of [[sociology]], though there are a number of independent demography departments.<ref name="ucb">UC Berkeley Demography department website.  http://demog.berkeley.edu/department/index.shtml</ref> '''Formal demography''' limits its object of study to the measurement of populations processes, while the broader field of social demography population studies also analyze the relationships between economic, social, cultural and biological processes influencing a population.<ref>Andrew Hinde ''Demographic Methods'' Ch. 1 ISBN 0-340-71892-7</ref>
 
The term [[demographics]] refers to characteristics of a population.
 
==Methods==
There are two types of data collection &mdash; direct and indirect &mdash; with several different methods of each type.
 
;Direct methods
Direct data come from vital statistics registries that track all births and deaths as well as certain changes in legal status such as marriage, divorce, and migration (registration of place of residence). In developed countries with good registration systems (such as the United States and much of Europe), registry statistics are the best method for estimating the number of births and deaths.
 
A [[census]] is the other common direct method of collecting demographic data. A census is usually conducted by a national government and attempts to enumerate every person in a country. However, in contrast to vital statistics data, which are typically collected continuously and summarized on an annual basis, censuses typically occur only every 10 years or so, and thus are not usually the best source of data on births and deaths. Analyses are conducted after a census to estimate how much over or undercounting took place. These compare the [[sex ratio]]s from the census data to those estimated from natural values and mortality data.
 
Censuses do more than just count people. They  typically collect information about families or households in addition to individual characteristics such as age, sex, marital  status, literacy/education, employment status, and occupation, angraphical location. They may also collect data on migration (or place of birth or of previous residence), language, religion, nationality (or ethnicity or race), and citizenship.  In countries in which the vital registration system may be incomplete, the censuses are also used as a direct source of information about fertility and mortality; for example the censuses of the [[People's Republic of China]] gather information on births and deaths that occurred in the 18 months immediately preceding the census.
[[File:World population.PNG|thumb|350px|Map of [[Country|countries]] by population]]
[[File:World population growth - time between each billion-person growth.svg|thumb|350px|Rate of human population growth showing projections for later this century.]]
 
;Indirect methods
Indirect methods of collecting data are required in countries and periods where full data are not available, such as is the case in much of the developing world, and most of [[historical demography]]. One of these techniques in contemporary demography is the sister method, where survey researchers ask women how many of their sisters have died or had children and at what age. With these surveys, researchers can then indirectly estimate birth or death rates for the entire population. Other indirect methods in contemporary demography include asking people about siblings, parents, and children. Other indirect methods are necessary in historical demography.
 
There are a variety of demographic methods for modeling population processes. They include [[models of mortality]] (including the [[life table]], [[Gompertz curve|Gompertz models]], [[Proportional hazards models|hazards models]], [[Proportional hazards models|Cox proportional hazards models]], [[Decrement table|multiple decrement life tables]], [[Brass relational logits]]), [[fertility]] ([[Hernes model]], [[Ansley J. Coale|Coale]]-Trussell models, [[parity progression ratios]]), marriage (Singulate Mean at Marriage, [[Page model]]), disability ([[Sullivan's method]], [[multistate life tables]]), [[population projections]] ([[Lee-Carter methods for estimating mortality|Lee Carter]], the [[Leslie matrix|Leslie Matrix]]), and [[population momentum]] ([[Nathan Keyfitz|Keyfitz]]).
 
== Common Rates and Ratios==
 
* The '''crude [[birth rate]]''', the annual number of live births per 1,000 people.
* The '''general [[fertility rate]]''', the annual number of live births per 1,000 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 1,000 women in particular age groups (usually age 15-19, 20-24 etc.)
* The '''crude [[death rate]]''', the annual number of deaths per 1,000 people.
* The '''[[infant mortality rate]]''', the annual number of deaths of children less than 1 year old per 1,000 live births.
* The '''expectation of life''' (or [[life expectancy]]), the number of years which an individual at a given age could 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 '''replacement level fertility''', the average number of children a woman must have in order to replace herself with a daughter in the next generation. For example the replacement level fertility in the US is 2.11. This means that 100 women will bear 211 children, 103 of which will be females. About 3% of the alive female infants are expected to decease before they bear children, thus producing 100 women in the next generation.<ref name="Ela 2008">Introduction to environmental engineering and science by Masters and Ela, 2008, Pearson Education, chapter 3</ref>
* 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.
* A '''stable population''', one that has had constant crude birth and death rates for such a long period of time that the percentage of people in every age class remains constant, or equivalently, the population pyramid has an unchanging structure.<ref name="Ela 2008"/>
* A '''stationary population''', one that is both stable and unchanging in size (the difference between crude birth rate and crude death rate is zero).<ref name="Ela 2008"/>
 
A stable population does not necessarily remain fixed in size. It can be expanding or shrinking.<ref name="Ela 2008"/>
 
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 1,000 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 proportionally 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 [[China]] as well.
 
==Basic equation==
Suppose that a country (or other entity) contains ''Population<sub>t</sub>'' persons at time ''t''.
What is the size of the population at time ''t'' + 1 ?
 
:<math>Population_{t+1} = Population_t + Natural increase_t + Net migration_t</math>
 
Natural increase from time ''t'' to ''t'' + 1:
 
:<math>Natural increase_t = Births_t - Deaths_t</math>
 
Net migration from time ''t'' to ''t'' + 1:
 
:<math>Net migration_t = Immigration_t - Emigration_t</math>
 
This basic equation can also be applied to subpopulations.  For example, the population size of ethnic groups or nationalities within a given society or country is subject to the same sources of change.  However, when dealing with ethnic groups, "net migration" might have to be subdivided into physical migration and ethnic reidentification ([[Cultural assimilation|assimilation]]).  Individuals who change their ethnic self-labels or whose ethnic classification in government statistics changes over time may be thought of as migrating or moving from one population subcategory to another.<ref>See, for example, Barbara A. Anderson and Brian D. Silver, "Estimating Russification of Ethnic Identity Among Non-Russians in the USSR," ''Demography'', Vol. 20, No. 4 (Nov., 1983): 461-489.</ref>
 
More generally, while the basic demographic equation holds true by definition, in practice the recording and counting of events (births, deaths, immigration, emigration) and the enumeration of the total population size are subject to error. So allowance needs to be made for error in the underlying statistics when any accounting of population size or change is made.
 
==History==
Demographic thoughts can be traced back to antiquity, and are present in many civilisations and cultures, like [[Ancient Greece]], [[Ancient Rome]], [[India]] and [[China]].<ref name="Srivastava2006">[http://books.google.es/books?id=oNcflpmW3BUC&pg=PA1&lpg=PA1&dq=studies+in+demography&source=bl&ots=Y1QFr3LGxP&sig=xJkW1mxVL6XS-Gij0tOpOsFZA9E&hl=es&ei=qdjRS8DjMsGC8gbj4Ii_Dw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCMQ6AEwAQ#v=onepage&q&f=false S.C.Srivastava,''Studies in Demography'',p.39-41]</ref> In ancient Greece, this can be found in the writings of [[Herodotus]], [[Thucidides]], [[Hippocrates]], [[Epicurus]], [[Protagoras]], [[Polus]], [[Plato]] and [[Aristotle]].<ref name="Srivastava2006" /> In Rome, writers and philosophers like [[Cicero]], [[Seneca the Younger|Seneca]], [[Pliny the elder]], [[Marcus Aurelius]], [[Epictetus]], [[Cato the Elder|Cato]] and Collumella also expressed important ideas on this ground.<ref name="Srivastava2006"/>
 
In the [[Middle ages]], Christian thinkers devoted much time in refuting the Classical ideas on demography.  Important contributors to the field were [[William of Conches]],<ref name="Biller2000">Peter Biller,''The measure of multitude: Population in medieval thought''[http://books.google.es/books?id=LnqlgqeYhwYC&pg=PA312&lpg=PA312&dq=Nicole+Oresme+on+demographics&source=bl&ots=1RB9HPQrvY&sig=RtvI_JuQ4SGR0QYfa7ptB5eDW1w&hl=es&ei=kdLRS8SJBcO78gbWg8jNDw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBkQ6AEwAA#v=onepage&q&f=false].</ref> [[Bartholomew of Lucca]],<ref name="Biller2000" /> [[William of Auvergne, Bishop of Paris|William of Auvergne]],<ref name="Biller2000" /> [[William of Pagula]],<ref name="Biller2000" /> and [[Ibn Khaldun]].<ref>See, e.g., [[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.</ref>
 
The ''Natural and Political Observations ... upon the Bills of Mortality'' (1662) of [[John Graunt]] contains a primitive form of [[actuarial table|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.</ref> 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).</ref>
 
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 [[Human overpopulation|overpopulation]] and the limits to growth. Later, more sophisticated and realistic models were presented by [[Benjamin Gompertz]] and [[Pierre François Verhulst|Verhulst]].
 
The period 1860-1910 can be characterized as a period of transition wherein demography emerged from statistics as a separate field of interest. This period included a panoply of international ‘great demographers’ like [[Adolphe Quételet]] (1796–1874), [[William Farr]] (1807–1883), [[Louis-Adolphe Bertillon]] (1821–1883) and his son [[Jacques Bertillon|Jacques]] (1851–1922), [[Joseph Körösi]] (1844–1906), [[Anders Nicolas Kaier]] (1838–1919), [[Richard Böckh]] (1824–1907), [[Émile Durkheim]] (1858-1917), [[Wilhelm Lexis]] (1837–1914) and [[Luigi Bodio]] (1840–1920) contributed to the development of demography and to the toolkit of methods and techniques of demographic analysis.<ref>de Gans, Henk and Frans van Poppel (2000) Contributions from the margins. Dutch statisticians, actuaries and medical doctors and the methods of demography in the time of Wilhelm Lexis. Workshop on ‘Lexis in Context: German and Eastern& Northern European Contributions to Demography 1860-1910’ at the Max Planck Institute for Demographic Research, Rostock , August 28 and 29, 2000.</ref>
 
 
 
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.<ref>{{cite journal|url=http://ace1.ma.utexas.edu/users/davis/375/reading/worldbirthrate.pdf|title=Doubling of world population unlikely|first=Wolfgang|last=Lutz|coauthors=Sanderson, Warren; Scherbov, Sergei|journal=Nature|volume=387|pages=803–805|date=1997-06-19|accessdate=2008-11-13|format=PDF|doi=10.1038/42935|pmid=9194559|issue=6635}}</ref> Throughout the 21st century, the average age of the population is likely to continue to rise.
 
===Science of population===
Populations can change through three processes: fertility, mortality, and migration.  Fertility involves the number of children that women have and is to be contrasted with fecundity (a woman's childbearing potential).<ref>John Bongaarts. The Fertility-Inhibiting Effects of the Intermediate Fertility Variables. Studies in Family Planning, Vol. 13, No. 6/7. (Jun. - Jul., 1982), pp. 179-189.</ref> Mortality is the study of the causes, consequences, and measurement of processes affecting death to members of the population. Demographers most commonly study mortality using the [[Life Table]], a statistical device which provides information about the mortality conditions (most notably the life expectancy) in the population.<ref>[http://www.cdc.gov/nchs/products/pubs/pubd/lftbls/lftbls.htm N C H S - Life Tables<!-- Bot generated title -->]</ref>
 
Migration refers to the movement of persons from a locality of origin to a destination place across some pre-defined, political boundary. Migration researchers do not designate movements 'migrations' unless they are somewhat permanent.  Thus demographers do not consider tourists and travelers to be migrating. While demographers who study migration typically do so through census data on place of residence, indirect sources of data including tax forms and labor force surveys are also important.<ref>Donald T. Rowland ''Demographic Methods and Concepts'' Ch. 11 ISBN 0-19-875263-6</ref>
 
Demography is today widely taught in many universities across the world, attracting students with initial training in social sciences, statistics or health studies. Being at the crossroads of several disciplines such as [[sociology]], [[economics]], [[epidemiology]], [[geography]], [[anthropology]] and [[history]], demography offers tools to approach a large range of population issues by combining a more technical quantitative approach that represents the core of the discipline with many other methods borrowed from social or other sciences. Demographic research is conducted in universities, in research institutes as well as in statistical departments and in several international agencies. Population institutions are part of the [[Cicred]] (International Committee for Coordination of Demographic Research) network while most individual scientists engaged in demographic research are members of the International Union for the Scientific Study of Population,<ref>[http://www.iussp.org International Union for the Scientific Study of Population]</ref> or a national association such as the [[Population Association of America]] in the United States,<ref>[http://www.populationassociation.org Population Association of America]</ref> or affiliates of the Federation of Canadian Demographers in Canada.<ref>[http://www.canpopsoc.org Canadian Population Society]</ref>
 
==See also==
{{Commons category|{{PAGENAME}}}}
{{col-begin}}
{{col-2}}
* [[Biodemography]]
* [[Biodemography of human longevity]]
* [[Demographic analysis]]
* [[Demographic economics]]
* [[Historical demography]]
* [[Linguistic demography]]
* [[Nurgaliev's law]]
* [[Religious demography]]
* [[Political demography]]
* [[Gompertz-Makeham law of mortality]]
* [[Medieval demography]]
* [[National Security Study Memorandum 200]] of 1974
* [[Population]]
* [[Population geography]]
* [[Population projection]]
* [[Population reconstruction]]
* [[Population statistics]]
* [[Replacement migration]]
* [[Reproductive health]]
 
{{col-2}}
Social surveys:
*[[Current Population Survey]] (CPS)
*[[Demographic and Health Surveys]] (DHS)
*[[Reproductive Health Survey]] (RHS)
*[[European Social Survey]] (ESS)
*[http://www.unece.org/pau/ffs/ffs.htm Family and Fertility Surveys] (FFS)
*[[General Social Survey]] (GSS)
*[[German General Social Survey]] ([[ALLBUS]])
* ''German'' [[Socio-Economic Panel]] (SOEP)
*[[National Longitudinal Survey]] (NLS)
*[[Panel Study of Income Dynamics]] (PSID)
*[[World Values Survey]] (WVS)
*[[Multiple Indicator Cluster Surveys]] (MICS)
Organizations:
* [http://www.unpopulation.org Population Division] (DESA) (United Nations)
* [[Office of Population Research]] (Princeton University) (United States)
* [[Population Reference Bureau]] (United States)
* [[Population Studies Center at the University of Michigan]] (United States)
* [[International Institute for Applied Systems Analysis]] (IIASA) non-governmental research institution
* [[Institut national d'études démographiques]] (INED) (France)
* [[Max Planck Institute for Demographic Research]] (Germany)
Scientific journals:
* ''[[Brazilian Journal of Population Studies]]''
*''[[Cahiers québécois de démographie]]'' (''Quebec Notebooks of Demography'')
{{Col-end}}
 
==Notes==
{{reflist|colwidth=30em}}
 
==Further reading==
{{Wikisource portal|Demography}}
* Josef Ehmer, Jens Ehrhardt, Martin Kohli (Eds.): [http://www.gesis.org/en/hsr/current-issues/current-issues-2010-2012/362-fertility/ ''Fertility in the History of the 20th Century: Trends, Theories, Policies, Discourses''].  [[Historical Social Research]] 36 (2), 2011.
* Glad, John. 2008. ''[http://www.whatwemaybe.org/txt/txt0000/Glad.John.2008.FHE.Meisenberg-abridgement.en.pdf Future Human Evolution: Eugenics in the Twenty-First Century]''. Hermitage Publishers, ISBN 1-55779-154-6
* Gavrilova N.S., Gavrilov L.A. 2011. Ageing and Longevity: Mortality Laws and Mortality Forecasts for Ageing Populations [In Czech: Stárnutí a dlouhověkost: Zákony a prognózy úmrtnosti pro stárnoucí populace].  Demografie,  53(2): 109-128.
* Preston, Samuel, Patrick Heuveline, and Michel Guillot. 2000. ''Demography: Measuring and Modeling Population Processes''. Blackwell Publishing.
* Gavrilov L.A., Gavrilova N.S.  2010. Demographic Consequences of Defeating Aging.  Rejuvenation Research, 13(2-3): 329-334.
* [[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
* Uhlenberg P.(Editor), (2009) International Handbook of the Demography of Aging, New York:  Springer-Verlag, pp.&nbsp;113–131.
* Paul Demeny and Geoffrey McNicoll (Eds.). 2003. The Encyclopedia of Population. New York, Macmillan Reference USA, vol.1, 32-37
* [[Phillip Longman]] (2004), ''The Empty Cradle: how falling birth rates threaten global prosperity and what to do about it''
* Sven Kunisch, Stephan A. Boehm, Michael Boppel (eds) (2011). ''From Grey to Silver: Managing the Demographic Change Successfully'', Springer-Verlag, Berlin Heidelberg, ISBN 978-3-642-15593-2
* Joe McFalls (2007), ''[http://prb.org/pdf07/62.1LivelyIntroduction.pdf Population: A Lively Introduction],'' [[Population Reference Bureau]]
* [[Ben J. Wattenberg]] (2004), ''How the New Demography of Depopulation Will Shape Our Future''. Chicago: R. Dee, ISBN 1-56663-606-X
 
== External links ==
{{Wiktionary|demography}}
{{Commons category|Demography}}
* {{dmoz|Science/Social_Sciences/Demography_and_Population_Studies/|Demography}}
* [http://www.historicalstatistics.org Historicalstatistics.org] Links to historical demographic and economic statistics
* [http://www.un.org/esa/population/unpop.htm United Nations Population Division: Homepage]
** [http://esa.un.org/unpd/wpp/index.htm World Population Prospects, the 2010 Revision], Population estimates and projections for 230 countries and areas
** [http://esa.un.org/unpd/wup/index.htm World Urbanization Prospects, the 2011 Revision], Estimates and projections of urban and rural populations and urban agglomerations
** [http://esa.un.org/unpd/ppp/index.htm Probabilistic Population Projections, the 2nd Revision], Probabilistic Population Projections, based on the 2010 Revision of the World Population Prospects.
* [http://www.aetheling.com/NL/sim/population/population1.html  Java Simulation of Population Dynamics].
* [http://gsociology.icaap.org/basicguide.html Basic Guide to the World: Population changes and trends, 1960 to 2003]
* [http://gsociology.icaap.org/report/demsum.html Brief review of world basic demographic trends]
 
 
{{Social sciences}}
 
[[Category:Demography| 01]]
[[Category:Demographics|.]]
[[Category:Actuarial science]]
[[Category:Branches of sociology (interdisciplinary)]]
[[Category:Environmental social science]]
[[Category:Human geography]]
[[Category:Population]]
[[Category:Sociology index]]
 
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Latest revision as of 14:50, 8 January 2015

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