Download The Demographic Transition

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
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
Performance Objectives
1. Examine patterns of natural
increase
2. Classify populations and subpopulations within the
demographic transition framework
3. Predict growth trends in
populations and sub-populations
Demography
 a kindred population science
 with epidemiology, it shares
the Greek root demos (people)
th
and the same founder, 17
century Englishman, John
Graunt
Demography is the scientific
study of the determinants and
consequences of human
population trends
By the beginning of the 21st
century, world population
reached 6 billion. Most of the
growth has occurred in the
past 200 years.
Figure 1 World Population Growth
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.
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.
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).
In his Essay on the Principle of
Population, initially published in
1798, Malthus postulated that
population tended to grow
geometrically (exponentially)
while the means of subsistence
(food) grew only arithmetically.
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…
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.
Owing to war, disease, hunger,
and vice, mortality would serve
as a positive check on
population growth.
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)
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
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.
The Demographic Transition
During the first half of
th
the 20 century,
demographers conceived
the notion of the
demographic transition.
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 VITAL RATES
Crude Death Rate (CDR) =
# deaths in calendar year * k
mid–year population
CRUDE VITAL RATES
Crude Birth Rate (CBR) =
# deaths in calendar year * k
mid–year population
Rate of Natural Increase =
CBR - CDR
Figure 2 The Demographic Transition
Source: Joseph A. McFalls, Jr. Population: A Lively Introduction.
Third edition. Population Reference Bureau 53(3); 1998: 39
Four Perspectives on
Demographic Transition
(1) Description
(2) Classification
(3) Explanation
(4) Prediction
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