Demography (from prefix demo- from
Ancient Greek δῆμος (dēmos) meaning 'the people', and -graphy from
γράφω (graphō) meaning 'writing, description or measurement') is the
statistical study of
populations, especially
human beings.
Demographic analysis can cover whole societies or groups defined by criteria such as
education,
nationality,
religion, and
ethnicity. Educational institutions usually treat demography as a field of
sociology, though there are a number of independent demography departments.
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 between economic, social, cultural, and biological processes influencing a population.
The 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).
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 that provides information about the mortality conditions (most notably the life expectancy) in the population.
Migration refers to the movement of persons from a locality of origin to a destination place across some 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 do so through census data on place of residence, indirect sources of data including tax forms and labour force surveys are also important.
- 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 in order to replace the population for the next generation. For example, the replacement level fertility in the US is 2.11.
- 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.
- A stationary population, one that is both stable and unchanging in size (the difference between crude birth rate and crude death rate is zero).
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.
