Demography

{{Short description|Study of human populations and their structures}} {{About-distinguish|the academic discipline|Demography (journal)|Demography (album)}} {{Use dmy dates|date=August 2016}} {{Use Oxford spelling|date=September 2015}}

alt=The Demography of the World Population from 1950 to 2100. Data source: United Nations — World Population Prospects 2017|thumb|350x350px|The Demography of the World Population from 1950 to 2100. Data source: United Nations — World Population Prospects 2017

'''Demography''' ({{etymology|grc|''{{wikt-lang|grc|δῆμος}}'' ({{grc-transl|δῆμος}})|people, society||''{{wikt-lang|grc|-γραφία}}'' ({{grc-transl|-γραφία}})|writing, drawing, description}})<ref>{{cite Merriam-Webster|demography}}</ref> is the statistical study of human populations: their size, composition (e.g., ethnic group, age), and how they change through the interplay of fertility (births), mortality (deaths), and migration.<ref>{{Cite web |title=Population: A Lively Introduction |url=https://www.prb.org/resources/population-a-lively-introduction/ |access-date=2025-03-17 |website=PRB |language=en-US}}</ref>

'''Formal demography''' limits its object of study to the measurement of population processes, while the broader field of '''social demography''' (or population studies) also analyses the relationships among economic, social, institutional, cultural, and biological processes that influence a population.<ref>{{cite web|title=The Science of Population |url=http://demographicpartitions.org/science-population-determines-population-change/ |website=demographicpartitions.org |access-date=4 August 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150814023915/http://demographicpartitions.org/science-population-determines-population-change/ |archive-date=14 August 2015 |df=dmy }}</ref> Educational institutions usually treat demography as a field of sociology, although independent demography departments do exist.<ref name="ub">{{Cite web | title=UC Berkeley Demography department website | url=http://www.demog.berkeley.edu/ | access-date=12 October 2006 | archive-date=1 September 2006 | archive-url=https://web.archive.org/web/20060901191409/http://www.demog.berkeley.edu/ | url-status=live }}</ref><ref>Andrew Hinde ''Demographic Methods'' Ch. 1 {{ISBN|0-340-71892-7}}</ref>

'''Demographic analysis''' (usually abbreviated to DA) examines and measures the dimensions and dynamics of populations, including whole societies or groups defined by criteria such as education, nationality, religion, and ethnicity.<ref name="census.gov">{{cite web|url=https://www.census.gov/coverage_measurement/demographic_analysis/|title=Coverage Measurement|author=US Census Bureau Webdesign: SSD, Laura K Yax, Content: DSSD, Phil Gbur, POP, Jason Devine|publisher=|accessdate=26 March 2016|archive-date=10 January 2016|archive-url=https://web.archive.org/web/20160110142138/http://www.census.gov/coverage_measurement/demographic_analysis/|url-status=live}}</ref> The methods of DA have primarily been developed to study human populations, but have also been used in a variety of areas where researchers want to know how other non-human populations of social actors can change across time through processes of birth, death, and migration.

Demographic analysis is used in a wide variety of contexts. In the labor force, DA is used to estimate sizes and flows of populations of workers; in population ecology the focus is on the birth, death, emigration and immigration of individuals in a population of living organisms; in the social sciences this could involve the movement of firms and institutional forms; in business planning DA is often used to describe the population in a business's geographic area.<ref>{{cite web|url=http://biztaxlaw.about.com/od/glossaryd/a/demographics.htm|title=How to Use Demographics for Business Advertising|author=Jean Murray|work=About.com Money|accessdate=26 March 2016|archive-date=6 October 2011|archive-url=https://web.archive.org/web/20111006194323/http://biztaxlaw.about.com/od/glossaryd/a/demographics.htm|url-status=dead}}</ref>

In the context of human biological populations, demographic analysis uses administrative records to develop an independent estimate of the population.<ref>{{Cite web |title=Demographic Analysis |url=https://govinfo.library.unt.edu/cmb/cmbp/downloads/da.pdf |access-date=3 October 2023 |website=U.S. Census Monitoring Board}}</ref> For example, '''patient demographics''' such as date of birth, gender, date of death, postal code, ethnicity, blood type, emergency contact information, family doctor, insurance provider data, allergies, major diagnoses, and major medical history form the core of the data for any medical institution, allowing the identification and categorization of a patient for the purpose of statistical analysis.<ref name="What Are Patient Demographics?">{{Cite web| title=What Are Patient Demographics?| date=21 December 2011| url=https://www.macadamian.com/learn/patient-demographics/| access-date=15 November 2020| archive-date=28 January 2021| archive-url=https://web.archive.org/web/20210128074040/https://www.macadamian.com/learn/patient-demographics/| url-status=live}}</ref>

Demographic analysis estimates are often considered a reliable standard for judging the accuracy of census information. For example, the U.S. Census Bureau expanded its DA categories for the 2010 U.S. Census to include comparative analysis between independent housing estimates, and differences between census address lists at different key times.<ref name="census.gov" />

==History== Demographic thought traces back to antiquity, and were present in many civilizations and cultures like Ancient Greece, Ancient Rome, China and India.<ref name="Srivastava2006">{{cite book| url = https://books.google.com/books?id=oNcflpmW3BUC&dq=studies+in+demography&pg=PA1| title = S.C.Srivastava, ''Studies in Demography'', p.39-41| isbn = 9788126119929| last1 = Srivastava| first1 = Sangya| date = December 2005| publisher = Anmol Publications Pvt. Limited}}</ref> Made up of the prefix ''demo-'' and the suffix ''-graphy'', the term ''demography'' refers to the overall study of population.<ref>{{Cite book |url=https://assets.cambridge.org/97811070/42674/excerpt/9781107042674_excerpt.pdf |title=Population and society |publisher=Cambridge University Press |isbn=978-1-107-04267-4 |edition=2 |pages=3 |chapter=An Introduction to Demography}}</ref>

In ancient Greece, this can be found in the writings of Herodotus, Thucydides, Hippocrates, Epicurus, Protagoras, Polus, Plato and Aristotle.<ref name="Srivastava2006" /> In Rome, writers and philosophers like Cicero, Seneca, Pliny the Elder, Marcus Aurelius, Epictetus, Cato, and Columella also expressed important ideas on this ground.<ref name="Srivastava2006" />

In the Middle Ages, Christian thinkers devoted much time to 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''[https://books.google.com/books?id=LnqlgqeYhwYC&dq=Nicole+Oresme+on+demographics&pg=PA312].</ref> Bartholomew of Lucca,<ref name="Biller2000" /> William of Auvergne,<ref name="Biller2000" /> William of Pagula,<ref name="Biller2000" /> and Muslim sociologists like Ibn Khaldun.<ref>See, e.g., Andrey Korotayev, Artemy Malkov, & Daria Khaltourina (2006). [https://www.academia.edu/32757085/Introduction_to_Social_Macrodynamics._Models_of_the_World_System_Development._Moscow_KomKniga_URSS_2006 ''Introduction to Social Macrodynamics: Compact Macromodels of the World System Growth''] {{Webarchive|url=https://web.archive.org/web/20190709103050/https://www.academia.edu/32757085/Introduction_to_Social_Macrodynamics._Models_of_the_World_System_Development._Moscow_KomKniga_URSS_2006 |date=9 July 2019 }}. Moscow: URSS, {{ISBN|5-484-00414-4}}.</ref>

One of the earliest demographic studies in the modern period was ''Natural and Political Observations Made upon the Bills of Mortality'' (1662) by John Graunt, which contains a primitive form of life table. Among the study's findings were that one-third of the children in London died before their sixteenth birthday. 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>

In 1755, Benjamin Franklin published his essay ''Observations Concerning the Increase of Mankind, Peopling of Countries, etc.'', projecting exponential growth in British colonies.<ref name=valtier>{{cite journal|title="An Extravagant Assumption": The Demographic Numbers behind Benjamin Franklin's Twenty-Five-Year Doubling Period|last=von Valtier|first=William F.|journal=Proceedings of the American Philosophical Society|volume=155|number=2|date=June 2011|pages=158–188|url=http://www.amphilsoc.org/sites/default/files/proceedings/5VonValtier1550205.pdf|access-date=19 September 2018|archive-url=https://web.archive.org/web/20160305211515/https://amphilsoc.org/sites/default/files/proceedings/5VonValtier1550205.pdf|archive-date=5 March 2016|url-status=dead}}</ref> His work influenced Thomas Robert Malthus,<ref>{{cite journal |last=Zirkle |first=Conway |author-link=Conway Zirkle |date=April 25, 1941 |title=Natural Selection before the 'Origin of Species' |journal=Proceedings of the American Philosophical Society |location=Philadelphia, PA |publisher=American Philosophical Society |volume=84 |issue=1 |pages=71–123 |jstor=984852 |issn=0003-049X}}</ref> who, writing at the end of the 18th century, feared that, if unchecked, population growth would tend to outstrip growth in food production, leading to ever-increasing famine and poverty (see Malthusian catastrophe). Malthus is seen as the intellectual father of ideas of overpopulation and the limits to growth. Later, more sophisticated and realistic models were presented by Benjamin Gompertz and Verhulst.{{citation needed|date=August 2024}}

In 1855, Belgian scholar Achille Guillard defined demography as the natural and social history of the human species or the mathematical knowledge of populations, of their general changes, and of their physical, civil, intellectual, and moral condition.<ref>{{Cite book|title=Encyclopedia of the City|last=Caves|first=R. W.|publisher=Routledge|year=2004|pages=169}}</ref>

Newell (1988, p. 4-5) claims that the first major developments in the 20th century, in what was to become formal demography, were made in three papers by Alfred J. Lotka (1907, 1911 (with F.R. Sharpe), and 1922, where a Stable Population Model was developed. This model was similar to Leonhard Euler's earlier but overlooked modeling, which showed how a population with constant fertility and mortality might grow geometrically using a difference equation. Under this geometric growth model, Euler also examined relationships among various demographic indices, showing how they could be used to produce estimates when data were missing. Lotka (and Sharpe) showed that a closed population (assuming constant both age-specific mortality and fertility) developed along a path leading to a fixed age structure - The Stable Population.<ref>Newell, Colin. (1988) Methods and models in demography. Belhaven Press.</ref><ref>Inaba, Hisashi (2017) Chapter 1 The Stable Population Model in ''Age-structured population dynamics in demography and epidemiology''. Springer Singapore.</ref><ref>Lotka, A. J. (1907). Relation between birth rates and death rates. Science, 26(653), 21-22.</ref><ref>Sharpe, F. R., & Lotka, A. J. (1911). L. A problem in age-distribution. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 21(124), 435-438.</ref><ref>Lotka, A. J. (1922). The stability of the normal age distribution. Proceedings of the National Academy of Sciences, 8(11), 339-345.</ref>

==Methods== {{copyedit|date=February 2026}} thumb|Early censuses and surveys provided demographic data.

Demographic data collection can be direct, where the desired statistics are explicitly recorded, or indirect, where statistics must be estimated via proxy data.<ref name="un-manual-x">{{cite book | title = Manual X: Indirect Techniques for Demographic Estimation | series = Population Studies | volume = 81 | publisher = United Nations | location = New York | date = 1983 | id = ST/ESA/SER.A/81 | collaboration = Population Division of the Department of International Economic and Social Affairs; Committee on Population and Demography, National Research Council, United States National Academy of Sciences | url = https://www.un.org/en/development/desa/population/publications/pdf/mortality/Manual_X.pdf }}</ref>

=== Direct methods === Direct data comes from vital statistics registries that track births, deaths, and certain changes in legal status such as marriage, divorce, and migration (registration of place of residence). In developed countries, registry statistics are the most accurate method for estimating the number of births and deaths.<ref name="un-manual-x" />

A census is another common direct method for collecting demographic data. A national government usually conducts a census and attempts to enumerate every person in a country. In contrast to vital statistics data, which are typically collected continuously and summarized annually, censuses 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 the extent of over- or undercounting. These compare the sex ratios from the census data to those estimated from natural values and mortality data.

Censuses also typically collect information about families or households in addition to individual characteristics such as age, sex, marital status, literacy/education, employment status, occupation, and geographical location. They may also collect data on migration (or place of birth or of previous residence), language, religion, nationality, ethnicity/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.{{cn|date=February 2026}}

[[File:Población Mundial.svg|thumb|Map of countries by population]] thumb|upright=1.6|Rate of human population growth showing projections for later this century<ref>{{cite journal | url = https://ourworldindata.org/world-population-growth#how-long-did-it-take-for-the-world-population-to-increase-by-one-billion | author1 = Max Roser | author1-link = Max Roser | author2 = Hannah Ritchie | author2-link = Hannah Ritchie | author3 = Esteban Ortiz-Ospina | author4 = Lucas Rodés-Guirao | title = How long did it take for the world population to increase by one billion? | journal = Our World in Data | year = 2013 | access-date = 25 November 2022 | archive-date = 13 October 2016 | archive-url = https://web.archive.org/web/20161013144559/https://ourworldindata.org/world-population-growth/#how-long-did-it-take-for-the-world-population-to-increase-by-one-billion | url-status = live }}</ref><ref>{{Cite journal |last=Roser |first=Max |last2=Ritchie |first2=Hannah |date=2023-06-01 |title=How has world population growth changed over time? |url=https://ourworldindata.org/population-growth-over-time |journal=Our World in Data |language=en}}</ref>

=== Indirect methods === Indirect methods of data collection are required in countries and periods where full data are unavailable, as is the case in much of the developing world and in most of historical demography. One of these techniques in contemporary demography is the sister method, in which survey researchers ask women how many of their sisters have died or had children, and at what ages. 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.{{citation needed|date=May 2023}}

There are a variety of demographic methods for modelling population processes. They include models of mortality (including the life table, Gompertz models, hazards models, Cox proportional hazards models, multiple decrement life tables, Brass relational logits), fertility (Hermes model, Coale-Trussell models, parity progression ratios), marriage (Singulate Mean at Marriage, Page model), disability (Sullivan's method, multistate life tables), population projections (Lee-Carter model, the Leslie Matrix), and population momentum (Keyfitz).

The United Kingdom has a series of four national birth cohort studies, the first three spaced apart by 12 years: the 1946 National Survey of Health and Development, the 1958 National Child Development Study,<ref>{{cite journal |author=Power C and Elliott J |title=Cohort profile: 1958 British Cohort Study |journal=International Journal of Epidemiology |volume=35 |issue=1 |pages=34–41 |year=2006 |pmid=16155052 |doi=10.1093/ije/dyi183|doi-access=free }}</ref> the 1970 British Cohort Study,<ref>{{cite journal |author=Elliott J and Shepherd P|title=Cohort profile: 1970 British Birth Cohort (BCS70)|journal=International Journal of Epidemiology |volume=35 |issue=4 |pages=836–43|year=2006 |doi=10.1093/ije/dyl174 |pmid=16931528|doi-access=free }}</ref> and the Millennium Cohort Study, begun much more recently in 2000. These have followed the lives of samples of people (typically beginning with around 17,000 participants in each study) for many years and are still ongoing. As the samples have been drawn in a nationally representative way, inferences can be drawn from these studies about the differences between four distinct generations of British people in terms of their health, education, attitudes, childbearing and employment patterns.<ref>The last three are run by the [http://www.cls.ioe.ac.uk Centre for Longitudinal Studies] {{Webarchive|url=https://web.archive.org/web/20181028075855/http://www.cls.ioe.ac.uk/ |date=28 October 2018 }}</ref>

Indirect standardization is used when a population is small enough that the number of events (births, deaths, etc.) is also small. In this case, methods must be used to produce a standardized mortality rate (SMR) or standardized incidence rate (SIR).<ref>{{cite web |url=http://www.geo.hunter.cuny.edu/~imiyares/standard.htm |title=Direct and Indirect Standardization of Mortality Rates |accessdate=26 March 2016 |url-status=dead |archiveurl=https://web.archive.org/web/20160403114527/http://www.geo.hunter.cuny.edu/~imiyares/standard.htm |archivedate=3 April 2016 }}</ref><ref>{{Cite web |url=http://www.cid.harvard.edu/cidstudents/thesis_prize/thesis_2001/appendix_a.pdf |title=examples of standardization |access-date=16 October 2022 |archive-date=7 July 2017 |archive-url=https://web.archive.org/web/20170707210711/http://www.cid.harvard.edu/cidstudents/thesis_prize/thesis_2001/appendix_a.pdf |url-status=live }}</ref>

==Standardization of population numbers== For a comparison to be statistically significant, numbers must be adjusted for the size of the population being studied. For example, the fertility rate is calculated as the ratio of births among women of childbearing age to the total number of women in that age range. If these adjustments were not made, we would not know whether a nation with a higher birth or death rate has a population with more women of childbearing age or more births per eligible woman.{{citation needed|date=May 2023}}

Within the category of standardization, there are two major approaches: direct standardization and indirect standardization.<ref>{{Cite journal |last=Naing |first=N. N. |date=January 2000 |title=Easy way to learn standardization : direct and indirect methods |journal=The Malaysian Journal of Medical Sciences |volume=7 |issue=1 |pages=10–15 |issn=1394-195X |pmc=3406211 |pmid=22844209}}</ref>

==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). * The '''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 that 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 women must have to replace the population for the next generation. For example, the replacement level fertility in the US is 2.11.<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"/> * Measures of centralisation are concerned with the extent to which an area's population is concentrated in its urban centres.<ref>Hoyt, H., [https://www.jstor.org/stable/2769393 Forces of Urban Centralization and Decentralization], American Journal of Sociology, Vol. 46, No. 6 (May, 1941), pp. 843-852, accessed 2 July 2023</ref><ref>Cooper-Douglas, E., [https://www.abc.net.au/news/2023-01-06/population-outside-hobart-means-struggle-for-services/101829418 Tasmania forecast to have 79,000 more residents by 2033, with most living outside Greater Hobart], ''ABC News'', published 5 January 2023, accessed 2 July 2023</ref>

A stable population does not necessarily remain fixed in size. It can be expanding or shrinking.<ref name="Ela 2008"/>

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 in 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 summarizes mortality separately at each age. A life table is necessary to give a good estimate of life expectancy.

==Basic equation regarding development of a population== 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>\text{Population}_{t+1} = \text{Population}_t + \text{Natural Increase}_t + \text{Net Migration}_t</math>

Natural increase from time ''t'' to ''t'' + 1:

:<math>\text{Natural Increase}_t = \text{Births}_t - \text{Deaths}_t</math>

Net migration from time ''t'' to ''t'' + 1:

:<math>\text{Net Migration}_t = \text{Immigration}_t - \text{Emigration}_t</math>

These basic equations 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. When dealing with ethnic groups, however, "net migration" might have to be subdivided into physical migration and ethnic reidentification (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 by definition, in practice, the recording and counting of events (births, deaths, immigration, emigration) and the enumeration of the total population are subject to error. So allowance needs to be made for errors in the underlying statistics when accounting for population size or change.

The figure in this section shows the latest (2004) UN (United Nations) WHO 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 of 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 |author2=Sanderson, Warren |author3=Scherbov, Sergei |journal=Nature |volume=387 |pages=803–805 |date=1997-06-19 |access-date=2008-11-13 |doi=10.1038/42935 |pmid=9194559 |issue=6635 |bibcode=1997Natur.387..803L |s2cid=4306159 |url-status=dead |archive-url=https://web.archive.org/web/20081216230409/http://ace1.ma.utexas.edu/users/davis/375/reading/worldbirthrate.pdf |archive-date=16 December 2008 |df=dmy }}</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 refers to the number of children a woman has and should 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 in members of the population. Demographers most commonly study mortality using the life table, a statistical device that provides information about the mortality conditions (most notably the life expectancy) in the population.<ref>{{cite web| url = https://www.cdc.gov/nchs/products/pubs/pubd/lftbls/lftbls.htm| title = N C H S - Life Tables| access-date = 9 September 2017| archive-date = 29 July 2020| archive-url = https://web.archive.org/web/20200729200625/https://www.cdc.gov/nchs/products/pubs/pubd/lftbls/lftbls.htm| url-status = live}}</ref>

Migration refers to the movement of persons from a locality of origin to a destination place across a predefined political boundary. Migration researchers do not designate movements 'migrations' unless they are somewhat permanent. Thus, demographers do not consider tourists and travellers to be migrating. While demographers who study migration typically rely on census data on place of residence, indirect data sources, including tax forms and labour force surveys, are also important.<ref>Donald T. Rowland ''Demographic Methods and Concepts'' Ch. 11 {{ISBN|0-19-875263-6}}</ref>

Demography is widely taught today at many universities around the world, attracting students with initial training in the 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, research institutes, statistical departments, and 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>{{cite web| url = http://www.iussp.org/| title = International Union for the Scientific Study of Population| access-date = 20 April 2008| archive-date = 6 September 2019| archive-url = https://web.archive.org/web/20190906221242/https://iussp.org/| url-status = live}}</ref> or a national association such as the Population Association of America in the United States,<ref>{{cite web| url = http://www.populationassociation.org/| title = Population Association of America| access-date = 14 April 2011| archive-date = 19 March 2011| archive-url = https://web.archive.org/web/20110319153140/http://www.populationassociation.org/| url-status = live}}</ref> or affiliates of the Federation of Canadian Demographers in Canada.<ref>{{Cite web |url=https://fcdweb.wordpress.com/ |title=Fédération canadienne de démographie – Federation of Canadian Demographers |access-date=7 December 2022 |archive-date=7 February 2023 |archive-url=https://web.archive.org/web/20230207210924/https://fcdweb.wordpress.com/ |url-status=live }}</ref>

==Population composition== thumb|upright=1.3|World demography by age composition from 1950 to 2100 (projected).<ref name="q917">{{cite web | title=Population by age group | website=Our World in Data | url=https://ourworldindata.org/grapher/population-by-age-group | access-date=26 January 2025}}</ref> '''Population composition''' is the description of a population defined by characteristics such as age, race,<ref name="r344">{{cite journal | last1=Verdugo | first1=Richard R. | last2=Swanson | first2=David A. | title=The decline of the non‐Hispanic white population in the United States of America | journal=Social Science Quarterly | volume=105 | issue=3 | date=2024 | issn=0038-4941 | doi=10.1111/ssqu.13368 | pages=528–543 | url=https://onlinelibrary.wiley.com/doi/10.1111/ssqu.13368 | access-date=2026-05-02}}</ref> sex, or marital status. These descriptions can be necessary for understanding the social dynamics from historical and comparative research. These data are often compared using a population pyramid.

Population composition is also a very important part of historical research. Information ranging back hundreds of years is not always worthwhile, because the number of people for whom data are available may not provide the information that is important (such as population size). A lack of information about the original data-collection procedures may prevent an accurate evaluation of data quality.

==Population change== thumb|upright=1.3|Change in ethnic population composition from 1990 to 2020 in the USA.<ref name="r344"/> Population change is analyzed by measuring the difference between two population sizes. Global population continues to rise, which makes population change an essential component of demographics. This is calculated by subtracting the population size from an earlier census from the current population size. The best way to measure population change is to use the intercensal percentage change. The intercensal percentage change is the absolute change in population between the censuses divided by the population size in the earlier census. Next, multiply this by a hundredfold to receive a percentage. When this statistic is achieved, the population growth between two or more nations of different sizes can be accurately measured and examined.<ref>{{Cite web |url=https://www.census.gov/prod/2004pubs/wp02-1.pdf |title=Global Population at a Glance: 2002 and Beyond |access-date=16 October 2022 |archive-date=6 January 2022 |archive-url=https://web.archive.org/web/20220106210322/https://www.census.gov/prod/2004pubs/wp02-1.pdf |url-status=live }}</ref><ref>{{Cite web |title=Global Population Profile: 2002 |url=https://www.census.gov/prod/2004pubs/wp-02.pdf |url-status=dead |archive-url=https://web.archive.org/web/20220201180245/https://www.census.gov/prod/2004pubs/wp-02.pdf |archive-date=2022-02-01 |access-date=2023-10-03 |website=census.gov}}</ref> The population can change in terms of population composition.<ref name="r344"/>

==Effects== The long-term sustainability of a population is described by the demographic sustainability.<ref name="n175">{{cite journal | last=Stern | first=Eliahu | title=Demographic sustainability and rural development policy | journal=Journal of Maps | volume=9 | issue=2 | date=2013 | issn=1744-5647 | doi=10.1080/17445647.2013.773566 | pages=154–160 | url=https://www.tandfonline.com/doi/full/10.1080/17445647.2013.773566 | access-date=2026-04-15}}</ref> The sustainability of contemporary pay-as-you-go pensions depends on sustainable demographics and total fertility rates.<ref>{{cite book |title=Financial Sustainability of Pension Systems |series=Financial and Monetary Policy Studies |date=2021 |volume=52 |doi=10.1007/978-3-030-74454-0 |isbn=978-3-030-74453-3 }}{{pn|date=November 2025}}</ref>

===Turnover and in internal labor markets=== People decide to leave organizations for many reasons, such as better job opportunities, dissatisfaction, and family concerns. The causes of turnover can be split into two factors: one linked to the organization's culture, and the other to all other factors. People who do not fully accept a culture might leave voluntarily. Or, some individuals might leave because they fail to fit in or change within a particular organization.{{Citation needed|date=April 2026}}

===Organizational ecology===

A basic definition of population ecology is the study of the distribution and abundance of organisms. In relation to organizations and demography, organizations face various liabilities that affect their continued survival. Hospitals, like all other large and complex organizations, are impacted by the environment in which they work. For example, a study examined the closure of acute care hospitals in Florida during a specific period. The study examined the effect size, age, and niche density of these particular hospitals. A population theory says that organizational outcomes are mostly determined by environmental factors. Among the theory's several factors, four apply to the hospital closure example: size, age, the density of niches in which organizations operate, and the density of niches in which organizations are established.{{citation needed|date=May 2023}}

Problems in which demographers may be called upon to assist business organizations include determining the best prospective location for a branch store or service outlet, predicting demand for a new product, and analysing certain dynamics of a company's workforce. Choosing a new location for a branch of a bank, choosing the area in which to start a new supermarket, consulting a bank loan officer that a particular location would be a beneficial site to start a car wash, and determining what shopping area would be best to buy and be redeveloped in metropolis area are types of problems in which demographers can be called upon. Standardization is a useful demographic technique for analysing a business. It can be used as an interpretive and analytical tool for comparing different markets.{{Citation needed|date=April 2026}}

===Social surveys=== * Current Population Survey (CPS) * Demographic and Health Surveys (DHS) * European Social Survey (ESS) * General Social Survey (GSS) * German General Social Survey (ALLBUS) * Multiple Indicator Cluster Surveys (MICS) * National Longitudinal Survey (NLS) * Panel Study of Income Dynamics (PSID) * Performance Monitoring and Accountability 2020 (PMA2020) * Socio-Economic Panel (SOEP, German) * World Values Survey (WVS)

===Organizations=== * Global Social Change Research Project (United States) * Institut national d'études démographiques (INED) (France) * Max Planck Institute for Demographic Research (Germany) * Office of Population Research (Princeton University) (United States) * Population Council (United States) * Population Studies Center at the University of Michigan (United States) * Vienna Institute of Demography (VID) (Austria) * Wittgenstein Centre for Demography and Global Human Capital (Austria)

===Scientific journals=== * ''Brazilian Journal of Population Studies'' * ''Cahiers québécois de démographie'' * ''Demography'' * ''Population and Development Review'' {{div col end}}

== References == {{reflist}}

==Further reading== * Josef Ehmer, Jens Ehrhardt, Martin Kohli (Eds.): [https://web.archive.org/web/20130527141349/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}} * Andrey Korotayev & Daria Khaltourina (2006). [https://www.academia.edu/35443515/Introduction_to_Social_Macrodynamics_Compact_Macromodels_of_the_World_System_Growth._Moscow_KomKniga_2006 ''Introduction to Social Macrodynamics: Compact Macromodels of the World System Growth''. Moscow: URSS] {{ISBN|5-484-00414-4}} [http://urss.ru/cgi-bin/db.pl?cp=&page=Book&id=34250&lang=en&blang=en&list=14] * Uhlenberg P. (Editor), (2009) International Handbook of the Demography of Aging, New York: Springer-Verlag, pp. 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), ''Population: A Lively Introduction,'' Population Reference Bureau [http://prb.org/Publications/PopulationBulletins/2007/PopulationALivelyIntroduction.aspx] {{Webarchive|url=https://web.archive.org/web/20130601045452/http://www.prb.org/Publications/PopulationBulletins/2007/PopulationALivelyIntroduction.aspx |date=1 June 2013 }} * Ben J. Wattenberg (2004), ''How the New Demography of Depopulation Will Shape Our Future''. Chicago: R. Dee, {{ISBN|1-56663-606-X}} * Perry, Marc J. & Mackun, Paul J. ''Population Change & Distribution: Census 2000 Brief''. (2001) * Preston, Samuel; Heuveline, Patrick; and Guillot Michel. 2000. ''Demography: Measuring and Modeling Population Processes''. Blackwell Publishing. * Schutt, Russell K. 2006. "Investigating the Social World: The Process and Practice of Research". SAGE Publications. * Siegal, Jacob S. (2002), ''Applied Demography: Applications to Business, Government, Law, and Public Policy''. San Diego: Academic Press. * Wattenberg, Ben J. (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}} {{Wikisource portal|Demography}} * [https://web.archive.org/web/20160304072527/https://www.peeparound.com/ Quick demography data lookup] (archived 4 March 2016) * [http://www.historicalstatistics.org/ Historicalstatistics.org] Links to historical demographic and economic statistics * [https://www.un.org/development/desa/pd/ United Nations Population Division: Homepage] ** [https://web.archive.org/web/20110506065230/http://esa.un.org/unpd/wpp/index.htm World Population Prospects, the 2012 Revision], Population estimates and projections for 230 countries and areas (archived 6 May 2011) ** [https://www.un.org/en/development/desa/publications/world-urbanization-prospects-the-2011-revision.html World Urbanization Prospects, the 2011 Revision], Estimates and projections of urban and rural populations and urban agglomerations ** [https://web.archive.org/web/20121213035405/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 (archived 13 December 2012) * [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, 1960–2003] * [http://gsociology.icaap.org/report/demsum.html Brief review of world basic demographic trends] * [https://unece.org/population/fertility-and-family-survey-ffs Family and Fertility Surveys] (FFS)

Category:Demography Category:Actuarial science Category:Environmental social science Category:Interdisciplinary subfields of sociology Category:Human geography Category:Market segmentation Category:Human populations