Derived from the Greek word demos meaning ‘people’, demography, as defined in the United Nations Multilingual Demographic Dictionary, is the “scientific study of human populations, primarily with respect to their size, their structure and their development”.

The word was probably first used by the Frenchman A. Guillard in his textbook Elements de Statistique Humaine. However, it is generally agreed that the systematic collection and study of population statistics originated with the publication of Natural and Political Observations on the Bills of Mortality by John Gaunt in 1662. Demography is the analysis of population variables.

It includes both methods and substantive results in the fields of mortality, fertility, migrants and resulting population numbers. Demographers collect data on population and its components of change, and contribute to the wider field of population studies that relate population changes to non- demographic (social, economic, and political) or other factors.

Population variables are of two kinds-stock and flow. The important source of information on stock variables is national censuses, whose modem form goes back to the 17th century in Canada, Virginia, Sweden, and a few other places, and which are now carried out periodically in nearly all countries of the world. Among the cross-sectional information collected in censuses are age and sex distribution, labour force, status and occupation, and birthplace.

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The flow variables, the components of population change, include birth and death registrations, were initiated before the 19th century in Sweden and Britain, and are now routine in all industrial countries. Efforts to attain completeness are slowly making their way elsewhere.

Migration statistics, collected at national frontiers are not so easily available and are less reliable than birth and death registration. Much additional information including statistics of birth expectations is collected by sample surveys.