Demography is the study of human populations. It encompasses the study of the size, structure and distribution of populations, and how populations change through time due to births, deaths, migration and ageing, as well as other broader features of the population such as levels of education, nationality, religion and ethnicity.
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 Great Britain in 1801. See also Demographic statistics.
In many countries, particularly in the third world, reliable demographic data is still difficult to obtain. For example, during the 1980s the population of Nigeria was widely estimated to be around 130 million, before it was established to be 89 million in a census carried out in 1991.
Important concepts in Demography include:
- The birth rate, the number of live births per 1000 women of childbearing age (often taken to be from 15 to 49 years old).
- The mortality rate or death rate, the number of deaths per 1000 people.
- The infant mortality rate, the number of deaths of children less than 1 year old per 1000 live births.
Note that mortality rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1000 people is often much higher for developed nations than third world 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.
History
Among the earliest contributions to demographics were the works of Thomas Malthus. Malthus observed that, if unchecked, populations would grow exponentially. He feared that population growth would tend to outstrip growth in food production, leading to ever increasing famine and poverty. See malthusian catastrophe.
The Demographic Transition
Contrary to Malthus' predictions, 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 growth in preindustrial societies, followed by fast growth as the society develops and industrialises, followed by slow growth again as it becomes more affluent, is known as the demographic transition.