Introduction to population pyramidsPresentation Transcript
What are Population Pyramids?
The population composition or structure of a country
population pyramid or age-sex pyramid
Males and Females
Figures for males are recorded on the left of the diagram.
Figures for females are recorded on the right of the diagram.
Males and Females
The division between the sexes can also be analysed by calculating the
male : female ratio
or sex ratio
This expresses the number of men in the population as a proportion of the number of women.
The horizontal axis may either represent
the percentage of
the total population in each age category.
The population is normally divided into five year groups e.g. 0-4, 5-9, 10-14 on the vertical axis.
However, sometimes you will see one and ten year intervals too.
The final years are collapsed into one category (e.g. 90+)
Different age groups are known as cohorts
Five Year Cohorts
Population Pyramids Developing Countries
Wide base which indicates a youthful population (as a result of high birth rates);
Narrow top (there are fewer people in the older age groups because life expectancy is lower);
Sudan – a typical developing country pyramid
Implications for governments in developing countries
Limited resources will be stretched to meet the needs of a large number of dependent children for schooling, nutrition and health care;
As this group reaches working age, a large number of jobs will need to be created to enable them to support themselves and their families.
As this group reaches child-bearing age, it is likely that fertility rates will be high , leading to continued high rates of natural population increase.
Population Pyramids Developed Countries
Narrower base (due to lower birth rate)
WHY LOWER BIRTH RATES?
Wider top (reflecting a longer life expectancy)
WHY A LONGER LIFE EXPECTANCY?
In some developed countries there is a bulge in 40-45 age cohort as a result of the “baby boomers” of the 1960s
Japan – a typical developed country pyramid
An ageing population
The issues faced by many developed countries is of an ageing population where a smaller proportion of the population are of working age and are faced with the task of generating enough wealth to provide high levels of support for the elderly population.
The ratio of non-economically active to economically active people in the population is called the dependency ratio.
Zero Population Growth
The population pyramid can also show zero-growth.
This means that birth rates and death rates cancel each other out.
In this case, the age-sex pyramid is more like a column than a pyramid, and people are distributed evenly throughout the cohorts
Developed and Developing Countries
Past, Present and Future Trends
As well as illustrating the effect of past changes, population pyramids can also indicate both short and long term future changes in population.
We can use population pyramids to show the results of migration
Canada change over time
Characteristic of Population Pyramids - Summary
A wide base suggests a high birth rate, a high proportion of young people and thus a rapidly growing population
A narrow base tells us that the birth rate has fallen
Straight or near vertical sides tell us that the death rate is low
Sides that narrow inwards from the bottom show a high death rate
Large numbers of males around 20-34 year groups suggest high rates of immigration.
A small number of young people indicates high rates of outmigration