population growth and the demographic transition ian rh rockett, phd, mph professor and associate...
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Population Growth and the Demographic Transition
Ian RH Rockett, PhD, MPHProfessor and Associate Chair
Department of Community MedicineWest Virginia University
PO Box 9190 Morgantown, WV 26506-9190
USA
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Learning Objectives
1. To view population growth from a Malthusian perspective
2. To calculate crude death rates, birth rates, rates of natural increase, and population doubling times
3. To comprehend the concept of the Demographic Transition
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Performance Objectives1. Examine patterns of natural
increase
2. Classify populations and sub-populations within the demographic transition framework
3. Predict growth trends in populations and sub-populations
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Demography
a kindred population science
with epidemiology, it shares the Greek root demos (people) and the same founder, 17th century Englishman, John Graunt
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Demography is the scientific study of the determinants and
consequences of human population trends
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By the beginning of the 21st century, world population
reached 6 billion. Most of the growth has occurred in the
past 200 years.
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Figure 1 World Population Growth
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 38
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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.
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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.
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T.R. Malthus, 1766-1834
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).
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In his 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.
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The Malthusian Trap
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…
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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.
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Owing to war, disease, hunger, and vice, mortality would serve
as a positive check on population growth.
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Solution to the Malthusian Trap
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)
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Population Explosion
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
20th century
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Population Explosion
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.
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The Demographic Transition
During the first half of the 20th century,
demographers conceived the notion of the
demographic transition.
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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)
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CRUDE VITAL RATES
Crude Death Rate (CDR) =
# deaths in calendar year * k
mid–year population
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CRUDE VITAL RATES
Crude Birth Rate (CBR) =
# deaths in calendar year * k
mid–year population
Rate of Natural Increase = CBR - CDR
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Figure 2 The Demographic Transition
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction. Third edition. Population Reference Bureau 53(3); 1998: 39
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Four Perspectives on Demographic Transition
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(1) Description
(2) Classification
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(3) Explanation
(4) Prediction
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Figure 3 Demographic/ Epidemiologic Transition Framework
Source: Ian R.H. Rockett. Population and Health: An Introduction to Epidemiology. Second edition. Population Reference Bureau 54(4); 1999: 9