State the concept of Age-Sex pyramid. Discuss the different types of age-sex pyramids. (20 marks)

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  • Define age-sex pyramid.
  • Discuss its types with examples and diagrams.
  • Conclude.


The age-sex structure of a population refers to the number of females and males in different age groups. A population pyramid is used to show the age-sex structure of the population.

The shape of the population pyramid reflects the characteristics of the population. The left side shows the percentage of males while the right side shows the percentage of women in each age group.

Expanding Populations

The age-sex pyramid of Nigeria as you can see is a triangular shaped pyramid with a wide base and is typical of less developed countries. These have larger populations in lower age groups due to high birth rates. If you construct the pyramids for Bangladesh and Mexico, it would look the same.

Age Sex Pyramid for expanding population

Constant Population

Australia’s age-sex pyramid is bell shaped and tapered towards the top. This shows birth and death rates are almost equal leading to a near constant population.

Constant Population Age Sex Pyramid

Declining Populations

The Japan pyramid has a narrow base and a tapered top showing low birth and death rates. The population growth in developed countries is usually zero or negative.

Declining Population Age Sex Pyramid