Demography is the statistical study of all populations. It can be a very general science that can be applied to any kind of dynamic population, that is, one that changes over time or space (see population dynamics). It encompasses the study of the size, structure and distribution of populations, and spatial and/or temporal changes in them in response to birth, migration, aging and death.
Demographic analysis can be applied to whole societies or to groups defined by criteria such as education, nationality, religion and ethnicity. In academia, demography is often regarded as a branch of either anthropology, economics, or sociology. Formal demography limits its object of study to the measurement of populations processes, while the more broad field of social demography population studies also analyze the relationships between economic, social, cultural and biological processes influencing a population.[1]
The term demographics is often used erroneously for demography, but refers rather to selected population characteristics as used in government, marketing or opinion research, or the demographic profiles used in such research.
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There are two methods of data collection: direct and indirect. 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.
The 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.
Censuses do more than just count people. They typically collect information about families or households, as well as about such individual characteristics as age, sex, marital status, literacy/education, employment status and occupation, and geographical 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.
Indirect methods of collecting data are required in countries where full data are not available, such as is the case in much of the developing world. One of these techniques 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 include asking people about siblings, parents, and children.
There are a variety of demographic methods for modeling 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 (Hernes 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, the Leslie Matrix), and population momentum (Keyfitz).
Important concepts in demography include:
A stable population does not necessarily remain fixed in size, it can be expanding or shrinking.[5]
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 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.
Suppose that a country (or other entity) contains Populationt persons at time t. What is the size of the population at time t + 1 ?
Natural increase from time t to t + 1:
Net migration from time t to t + 1:
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 (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.[6]
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.
Ibn Khaldun (1332-1406) is regarded as the "father of demography" for his economic analysis of social organization which produced the first scientific and theoretical work on population, development, and group dynamics. His Muqaddimah also laid the groundwork for his observation of the role of state, communication and propaganda in history.[7]
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,[8] followed later by Augustus de Morgan, ‘On the Application of Probabilities to Life Contingencies’, (1838).[9]
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 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 (1851-1922), Joseph Körösi (1844-1906), Anders Nicolas Kaier (1838-1919), Richard Böckh (1824-1907), 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. [10]
Contrary to Malthus' predictions and 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 pre-industrial societies, followed by fast growth as the society develops and industrializes, 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 spiraling 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.[11]
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.[13] Throughout the 21st century, the average age of the population is likely to continue to rise.
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).[14] 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.[15]
Migration refers to the movement of persons from an origin place 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.[16]
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 geography, economics, sociology or epidemiology, 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 – IUSSP or, in the United States, in the Population Association of America.
Organizations:
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Demography literally translated from the Greek term means a description of people. On the other hand, the United Nations (UN) Demographic Dictionary describes demography as the scientific study of human populations primarily with respect to size, their, structure and their development.
Demography therefore is concerned with the current size and characteristics of human populations, how they were attained, and how they are changing. Changes in the characteristics of human populations is governed by the three main Population Processes: Fertility, Mortality and Migration. In turn, when these processes act, there are corresponding Population Outcomes which include changes in Population Size, Age and Sex Structure, and Spatial Organization.
While these main processes are the primary concern of demographers, it proves invaluable should these things not be detached from their relationships with other disiplines. As such, demography draws and contributes to the other fields of sciences ranging from Health and Medicine and Teletraffic to the social sciences such as Sociology, Anthropology and Political Science.
Demography includes the study of human populations by statistical methods. Demographers basically deal with the measurements of the number of people in each region of the country:
Demographers also have to measure
Finally demographers measure migrations:
Data from statistical censuses are the basic inputs, but have to be augmented with input from questionnaires and surveys. The trends are extrapolated (projected forwards).
The practical purpose is that the output forms the basis for the prediction of number of customers for public and private services and products.
DEMOGRAPHY (from Gr. Sriµ os, people, and y peol) v, to write), the science which deals with the statistics of health and disease, of the physical, intellectual, physiological and economical aspects of births, marriages and mortality. The first to employ the word was Achille Guillard in his Elements de statistique humaine ou demographie comparee (1855), but the meaning which he attached to it was merely that of the science which treats of the condition, general movement and progress of population in civilized countries, i.e. little more than what is comprised in the ordinary vital statistics, gleaned from census and registration reports. The word has come to have a much wider meaning and may now be defined as that branch of statistics which deals with the life-conditions of peoples.
Categories: DED-DEP | Earth sciences
Demography studies the statistics of human populations. Demography is usually used to study dynamic (constantly changing) populations. It covers the study of the size, structure and distribution of these populations and the changes in these populations due to do births, deaths, migration and emigration. Demography can also be applied to entires groups defined by nationality, religion and ethnicity.
Formal demography limits its object of study to the measurement of populations processes, while the more broad field of social demography population studies also analyze the relationships between economic, social, cultural and biological processes influencing a population.
   | PopulationData.net - PopulationData.net : Toutes les populations du monde |
| | The Population Reference Bureau - Home - Population Reference Bureau |
| | Ed Stephan's Timeline of Demography - Ed Stephan Site Has Moved |
| | CensusScope - CensusScope: Census 2000 Data, Charts, Maps, and Rankings |
| | Max Planck Institute for Demographic Research - Max Planck Institute for Demographic Research |
| | Population Studies Center at the University of Michigan - Population Studies Center at the University of Michigan |
| | Historicalstatistics.org - Historia.se - Historicalstatistics.org |
| | Population Studies Center at the University of Pennsylvania - Population Studies Center : University of Pennsylvania |
| | Brief review of world basic demographic trends - world demographic trends |
| | United Nations Population Division Homepage - United Nations Population Division Home Page |
| | Center for Demography and Ecology at the University of Wisconsin,Madison - Center for Demography and Ecology UW-Madison |
| | Brief review of world socio-demographic trends - world social trends |
| | Committee for International Cooperation in National Research in Demography - Welcome to CICRED |
| | Department of Demography, University of California, Berkeley - Demography at UC Berkeley |
| | Département de démographie, Université de Montréal - Université de Montréal, Département de démographie |
| | Population Studies - Taylor & Francis Journals: Welcome |
| | Centre for Population Studies - Centre for Population Studies - Home |
| | Institute National d'Etudes Démographiques - [INED] Institut National Etudes Démographiques - Recherches sur la population et en démographie |
| | International Institute for Applied Systems Analysis (IIASA) - IIASA - Laxenburg, Austria |
| | PAA - Home - Population Association of America |
| | Rivista Italiana di Economia Demografia e Statistica RIEDS - SIEDS Società Italiana di Economia Demografia e Statistica - Italian Society of Economics Demography and Statistics |
| | Population and Health graduate program - Hopkins Population Center |
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