Population Structure

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Population Composition &
Structure

3. Population Structure.
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Population structure means the 'make up' or
composition of a population.

4. Population Composition & Structure
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• The most basic elements of population composition are
• Sex structure
• Age structure

5. Population Composition & Structure
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• Sex structure
• The most basic measurement is the sex ratio
• The number of males per 100 females
Sex ratio = # of males x 100
#of females

6. Population Composition & Structure
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• If
• Sex ratio > 100, there are more males than females
• Sex ratio < 100, there are more females than males
• Sex ratio = 100, there are equal #s of both sexes

7. Population Composition & Structure
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• Important factors that affect the sex ratio are:
• The differences in death rates between males and females
• The differences in net migration by gender
• The sex ratio of newborn infants

8. Population Composition & Structure
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• Sex ratios at birth, 2008
• World = 107
• US = 105
• China = 111
• Mexico = 105
• France = 105
• Mozambique = 104
Source: CIA World Factbook

9. Population Composition & Structure
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• Sex ratios change as age progresses
• Migration is a very significant factor

10. Sex Ratios by County, 2000
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11. Population Composition & Structure
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• Age Structure
• Affects economic and social behavior
• Primary determinant
• Birth rate
• Analysis of age structure
• Population pyramids

12. Population Composition & Structure
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• Population pyramids
• 5 year age groups or cohorts
• A cohort is a group of people who share a temporal (time) experience
• Youth
• Middle aged
• Old aged
• Baby Boomers
• Gen Xers
• Baby Boomerangs

13. Population Composition & Structure
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• Analysis of population structure is important because
• Future patterns of population growth
• Amongst which age cohorts
• Structure of dependent population relative to the working age/productive
population
• Dependency ratio

14. Dependency Ratio
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• Ratio of the dependent-age population (the young and the old) to the
working age population
• The purpose of the dependency ratio is to measure the # of
dependents that each 100 people in the productive years must
support

15. Dependency Ratio

16. Population Pyramids
A Population Pyramid is two back-
to-back bar graphs. One side of the
graph shows the number of males
while the other side shows females
in a particular population in five-year
age groups. These age groups are
also called COHORTS.
Thus, a Population Pyramid is AGE
and SEX DISTRIBUTION within a
country.
A pyramid graphically displays long
term trends in the birth and death
rates, as well as shorter term
impacts such as baby-booms, wars
and epidemics.

17. Population
Pyramids
Interpretation of this pyramid.
It narrows toward the top. The death rate is
higher among older people than among
younger people.
There are not as many people in their 20s as
in their 30s. The people in their 20s in 1961
were born at the end of the Depression and
the start of WWII. This was a time of
economic hardship and uncertainty. People
were having fewer children in this period.
In 1961, the pyramid had a wide base. Adding
the percentages for the three lowest age
cohorts, we learn that 35% of the population
was under 15. These are the “baby boomers,”
a large group of people born between 1947
and 1966 when the economy was growing and
prospering.

18. Population Pyramids
CONSTRUCTION
The X-axis illustrates
males and females.
Males are always shown
on the left and females
on the right.
The Y-axis is age
cohorts
Males and females can
be represented or
measured by the
absolute number OR as
a percentage of the total
population.

19. Population Pyramids
Types of Pyramids
Expansive — A broad base indicating
a high proportion of children, a rapid
rate of population growth, and a low
proportion of older people.
Stable growth — A structure with
indentations that even out and reflect
slow growth over a period.
Stationary — A narrow base and
roughly equal numbers in each age
group, tapering off at the older ages.
This pyramid shows an unchanging
pattern of fertility and mortality.
Declining — A high proportion of
aged persons and declining
numbers.

20. Population Pyramids
The triangular distribution is also be
called a pyramid or exponential
distribution.
In this example, the wide base
indicates a large number of children,
while the rapid narrowing shows that
many people die between each age
band.
The pyramid shows a population with
a high birth rate, a high death rate
and a short life expectancy. This
pattern is typical of less
economically developed countries.
Here, there may be little access and
incentive to use birth control, poor
environmental factors (e.g., lack of
clean water) and limited access to
health services.

21. Population Pyramids
Rapid Growth
The triangle shape
suggest rapid
population growth.

22. Population Pyramids
Slow Growth
The square-like
structure is slow
growth. The lump in
the pyramid between
the ages of about 35 to
50 is the post-World
War II "baby boom." As
this population ages
and climbs up the
pyramid, there will be a
much greater demand
for medical and other
geriatric services.

23. Population Pyramids
Negative Growth
The population is
shrinking due to a
low birth rate and
a stable death
rate. Increased
emigration may
also be a
contributor to a
declining
population.

24. Population Pyramids
The following data are age cohorts for different
countries of the world. Build a Population Pyramid
for each country and describe the growth pattern.
Males Females
0-19 20-39 40-59 60+ 0-19 20-39 40-59 60+
Canada 13 15 14 7 12 15 14 9
Kenya 28 15 5 2 27 15 5 2
Germany 11 15 14 10 10 14 13 14
Pakistan 27 15 7 2 25 14 7 2
Poland 14 15 13 7 14 14 14 10

25. Population Pyramids
The figures illustrate four
different patterns or
characteristics of
population growth.
For each figure, describe
the pattern (e.g., high birth
rate, high death rate) and
the type of pyramid (e.g.,
Expansive, Stationary).

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