demography - Important concepts, History, The demographic transition

A branch of sociology which studies the population patterns of the past, present, and future. Demography has been very important in estimating future trends in population growth in order to calculate the pressures on global resources.

Demography is the scientific study of human population dynamics. Formal demography limits its object of study to the measurement of populations processes, while the more broad field of population studies also analyze the relationships between economic, social, cultural and biological processes influencing the population.

The term demographics is often used erroneously for demography, but refers rather to selected population characteristics as used in marketing or opinion research, or the demographic profiles used in such research.

In many countries, particularly in the developing countries, reliable demographic data is still difficult to obtain; During the 1980s, for example, the population of Nigeria was widely estimated to be around 101 million people, before it was established to be as little as 89 million people (without adjustment for undercounting) in a census carried out in 1991.

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 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.

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.

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. What is the size of the population at time t + 1 ?

Populationt + 1 = Populationt + Naturalincreaset + Netmigrationt

Natural increase from time t to t + 1:

Naturalincreaset = Birthst − Deathst

Net migration from time t to t + 1:

Netmigrationt = Immigrationt − Emigrationt

History

The Natural and Political Observations ... 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 (though 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 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.

Similar trends are now becoming visible in ever more developing countries, so that far from spiralling out of control, world population growth is expected to slow markedly in the next century, coming to an eventual standstill or even declining. 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. 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. Throughout the 21st century, the average age of the population is likely to continue to rise.