The composition of a population according to age groups and gender is known as the age-sex structure. It can be represented by means of a population pyramid.
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Population pyramids
The vertical axis of a population pyrmaid has the population in age bands of 5 years and the horizontal axis shows that number or % of males and females. The pyramid shows longevity by its height.
Population pyramids can show:
· The results of births minus deaths in specific age groups
· The effects of migration
· The effects of events such as war, famine and disease
· An indication of the overall life expectancy of a country
Age structure can also be measured by a number of indices:
· The dependency ratio
· The support ratio
· The juvenility index
· The old-age index
The dependency ratio shows the relationship between the economically active (working) population and the non-economically active (dependent) population
Links between the DTM and age-sex structure