1. Population, Economy and Society
Age and Sex Structure

2. Age and Sex Structure
The age and sex structure of a population has many important implications for that population!
For example this structure:
Is the basic determinant of the nation’s labor supply
Influences requirements for basic goods and services
Influences school attendance
Influences economic activity
And most fundamentally, it influences a society’s basic reproductive capacity

3. Age and Sex Structure
Now recall our discussion of the basic measures of demographic processes!
The CBR and the CDR are highly sensitive to the age/sex composition of a population!
The age/sex structure or composition of a population at any time is the result of past trends in:
Fertility
Mortality
Migration

4. Age and Sex Structure
In turn, it influences the current levels of crude vital rates and the rate of population growth since births, deaths and migration occur with unequal frequency at different ages!
OK…We want to explore the following:
The current age and sex patterns in different regions of the world
The factors determining age and sex structure
The effects of age and sex structures on the demographic processes
Some of the social and economic implications of a population’s age and sex structure

5. Age and Sex Structure Sex Structure
Age/sex structure is usually described as a series of “sex ratios”.
Most commonly this is the “masculinity” ratio as it is computed as the number of males per 100 females.
The sex ration at birth in the US is ~105/100 or 105 male births per 100 female births.
Why are more males born?

6. Age and Sex Structure
Since ASMR’s are generally higher for males at every age these ratios tend to gradually decline with age and then fall below the 100 level!
The age at which this happens varies.
Beyond this age the number of females begins to exceed the number of males!
This can be quite exaggerated at the advanced ages!
We will see later that this associated with a process called the “feminization of old age”

7. Age and Sex Structure Sex Ratios Circa 2000

8. Age and Sex Structure Sex Ratios by Age U.S. 2000

9. Age and Sex Structure Age Structure
Although chronological age is an unambiguous concept, census reports on age are subject to a number of errors:
Deliberate misstatement
“Preferred digits”
Exaggeration of age at older ages
Carelessness in reporting
Ignorance of correct age

10. Age and Sex Structure U.S. 2000

11. The Dependency Ratio Pop 0-14 + Pop 65+
DR = X 100
Pop 15-64

12. Dependency Ratios Circa 2000
World L. America 85.7
MDC’s N. America 67.2
LDC’s Europe 55.9
Africa Oceania 66.9
E. Asia 69.4
S. Asia 85.0

13. Percent below age 15 and Over 65
MDC’s = 19% 15%
LDC’s = 34% 5%
Mid Africa = 47% 3%
South Asia = 37% 5%
L. America = 33% 6%
Europe = 18% 15%
N. America = 21% 13%

14. Median Age US

15. Reading a Population Pyramid
Sex 
Historical
events
Cohort/
generation 
Age/Year of Birth 
 Trends
Population Size 

16. Tracking the Baby Boom Generation Click the button below to see changes in the US population from :

17. Age and Sex Structure Factors determining age/sex structure Migration
Young males are most likely to migrate
Impact on the US
In the long term
In the short term
In small geographic areas
Internationally?
Labor surplus and deficit countries!

18. Age and Sex Structure Mortality Fertility
Mortality varies with age thus the pyramidal shape of the population pyramid
Higher rates for males affect it
Circumstances such as war can also affect it
In general changes in mortality don’t affect the age/sex structure as much as migration or changes in fertility!
Fertility
Of critical importance to the age/sex structure
Short term changes
Long term changes

19. Changes in fertility and mortality and age/sex structure

20. Age-Sex Structure of Botswana - 2020

21. Age and Sex Structure
The effects of age and sex structures on the demographic processes!
There is a sort of “feedback” effect here!
Captured in the notion of “Population Momentum”
The population processes determine the age/sex structure of a population and that age/sex structure drives the population processes!
The “Rectangularization” of the pyramid!

22. The “Feedback” effect and “Rectagularization”

23. Age and Sex Structure
Consequences of changes in the age and sex structure!
Education
In the MDC’s
In the LDC’s
The Economy

24. Age and Sex Structure Politics and Political Behavior Crime
In the MDC’s
In the LDC’s
Crime
Marriage Markets

25. Stable and Stationary Populations
A Stable population
The age structure remains unchanged
Fertility and mortality rates have remained unchanged for some time
There is no migration
Can be growth
A Stationary population
Is stable
Has achieved ZPG

26. Population Projections
“It is easy to predict everything except the future” (Nathan Keyfitz) (Taken from an old Chinese proverb)
Cautions about population projections!
It can be very difficult to forecast with accuracy
The longer the time period the greater the risk
Changes in fertility are generally the most problematic
Especially difficult in the LDC’s because of the lack of data

27. Population Projections
OK…So what are the current projections?
We often rely on the UN’s Population Division for our projections! (Our Census Bureau also does them)
They usually take the form of three “scenarios” which are based on assumptions about fertility and mortality (Remember that we said that fertility is the most critical element and remember that if we are talking about the world we don’t have to worry about migration but if we are talking about the US we do!)

28. Some Population Projections for the U.S.

29. Some population Projections for the World
Low 7.3 billion
Medium 8.9 billion
High billion
The world is currently growing at ~1.3% per year or a doubling time of 53 years!

30. Zero Population Growth ZPG
What are the consequences of achieving it now versus later?
Social?
Political?
Economic?
Either way there will be shifts in the age/sex structure that will necessitate adjustments in society!
ZPG in the world?