• The total population of an area depends upon changes
in the natural increase and migration.
• The natural increase (or decrease) is the difference
between the birth rate and the death rate.
• The birth rate is the number of live births in a year
for every 1000 people in the total population.
• The death rate is the number of people in every 1000
who die in a year.
• If the birth rate is higher then the total population
will increase. If the death rate is higher then the
total population will decrease.
The Demographic Transition
• The DTM describes a sequence of changes
in the relationship between birth rates and
• The model was produced using changes in
the natural increase in several
industrialised countries in western Europe
and North America.
• It suggests that the population growth
rates for all countries can be divided into
The model itself
• The rates of natural increase, births,
deaths, infant mortality and life
expectancy all affect the population
structure of a country.
• The population structure of a country
can be shown by a population or agesex pyramid.
Population pyramids show
• The total population divided into fiveyear age groups
• the percentage of people in each of
those age groups
• the percentage of males and females
in each age group
Population pyramids are
useful because they show:
• Trends in the birth rate, death rate, infant
mortality rate and life expectancy - these trends
can help a country to plan its future services, e.g.
more homes for the elderly if there is an ageing
population or fewer schools if there is a declining
• The effects of people migrating into or out of a
region or country.
• The proportion of the population who are
economically active and the proportion who are
dependent upon them (dependency ratio).