Population Growth and the Demographic Transition. Ian RH Rockett, PhD, MPH Professor and Associate Chair Department of Community Medicine West Virginia University PO Box 9190 Morgantown, WV 26506-9190 USA [email protected] Learning Objectives.
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a kindred population science
with epidemiology, it shares the Greek root demos (people) and the same founder, 17th century Englishman, John Graunt
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 38
The unprecedented population growth of modern times heightens interest in the notion of doubling time. Calculation of population doubling time is facilitated by the Law of 70.
If a population is growing at a constant rate of 1% per year, it can be expected to double approximately every 70 years
-- if the rate of growth is 2%, then the expected doubling time is 70/2 or 35 years.
English clergyman, Thomas Robert Malthus, was the first person to draw widespread attention to the two components of natural increase, births and deaths (fertility and mortality).
In his heightens interest in the notion of doubling time. Calculation of population doubling time is facilitated by the Essay on the Principle of Population, initially published in 1798, Malthus postulated that population tended to grow geometrically while the means of subsistence (food) grew only arithmetically.
The Malthusian Trap heightens interest in the notion of doubling time. Calculation of population doubling time is facilitated by the arithmetic growth (food): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10…geometric growth (population):1, 2, 4, 8, 16, 32, 64, 128, 256, 512…
Malthus argued that the difference between geometric and arithmetic growth caused a tension between the growth of population and that of the means of subsistence.-- this gap could not persist indefinitely.
Preventive checks: birth control through (1) later age at marriage. (2)abstinence from sex outside marriage.
(Malthus opposed artificial methods of birth control on moral grounds. Viewed contraception as a vice)
Contrary to Malthus’s prediction, mortality has not yet risen to curb world population growth.
< 1 billion people in 1800
6 billion by the end of the
Why was Malthus unable to foresee the population explosion (also known as the population bomb)?
He did not recognize the force of the Industrial Revolution, which produced exponential growth in the means of subsistence.
During the first half of the 20th century, demographers conceived the notion of the demographic transition.
The demographic transition framework illustrates population growth in terms of discrepancies and changes in two crude vital rates – mortality and fertility (ignores migration)
Crude Death Rate (CDR) =
# deaths in calendar year * k
Crude Birth Rate (CBR) =
# deaths in calendar year * k
Rate of Natural Increase = CBR - CDR
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 39
Source: Ian R.H. Rockett. Population and Health: An Introduction to Epidemiology. Second edition. Population Reference Bureau 54(4); 1999: 9