Home > Demography

1 Data and methods

Demography relies on the use of large amounts of data, including census returns and records of births, marriages and deaths. The earliest modern census was carried out in Britain in 1801. See also demographic statistics.

In many countries, particularly in the third world, reliable demographic data are still difficult to obtain. For example, during the 1980s the population of Nigeria was widely estimated to be around 110 million, before it was established to be as little as 89 million (without adjustment for undercounting) in a census carried out in 1991.

2 Important concepts

Important concepts in demography include:

• The crude birth rate, the annual number of live births per thousand people.
• The general fertility rate, the annual number of live births per 1000 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 1000 women in particular age groups (usually age 15-19, 20-24 etc.)
• The crude death rate, the annual number of deaths per 1000 people.
• The infant mortality rate, the annual number of deaths of children less than 1 year old per thousand live births.
• The expectation of life (or life expectancy), the number of years which an individual at a given age can 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 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 rate is the number of daughters who would be born to a woman according to current age-specific fertility and mortality rates.

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 relatively 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.

3 History

Among the earliest contributions to demography were the works of Thomas Malthus. 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 catastropheA Malthusian catastrophe sometimes known as a Malthusian check is a return to subsistence-level conditions as a result of agricultural (or, in later formulations, economic) production being eventually outstripped by growth in population. Theories of Malth); he is seen as the intellectual father of ideas of overpopulationOverpopulation may indicate any case in which the population of any species of animal may exceed the carrying capacity of its ecological niche. In common parlance, the term specifically refers to the relationship of human population to the planet Earth.. Later more sophisticated and realistic models were presented by e.g. Gompertz and Verhulst .