Population Growth and the Demographic Transition

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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
• irockett_at_hsc.wvu.edu

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Learning Objectives

• To view population growth from a Malthusian
  perspective
• To calculate crude death rates, birth rates,
  rates of natural increase, and population
  doubling times
• To comprehend the concept of the Demographic
  Transition

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Performance Objectives

• Examine patterns of natural increase
• Classify populations and sub-populations within
  the demographic transition framework
• 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 Traparithmetic growth (food)
1, 2, 3, 4, 5, 6, 7, 8, 9, 10geometric 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 Malthuss prediction, mortality has
  not yet risen to curb world population growth.
• lt 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
• midyear population

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CRUDE VITAL RATES

• Crude Birth Rate (CBR)
• deaths in calendar year k
• midyear 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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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