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. It’s shape 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.
1. Expanding Population Pyramid:
- The countries that are characterized by high birth rate and high death rate, typical of the first stage of demographic transition, shall have a very broad base, which narrows down rapidly giving a concave shape to the sides of the triangle.
- Birth rates were high and families were large, partly because people did not think of limiting them and partly because a large family was of an advantage.
- In working-class families, all the children could contribute to the family income. However, death rates were also very high because epidemic diseases such as bubonic plague, cholera, and typhoid had not been brought under control and tuberculosis were also very common.
- Moreover low standards of hygiene and nutrition meant that infant mortality rates were also high. It was, therefore, necessary to have a large family so that at least some of the children would live.
2. Large Population Structure:
- A large number of young people pyramid after 1950 great advances were made in medicine and that that begins to fall but the birthrate remained so the population expanded rapidly the resultant population structure shown in figure with the base of the pyramid is much wider than the top reflect in the large numbers of young people in the population.
3. Constant Population- Bell-Shaped Pyramid:
- Australia‘s age-sex pyramid is bell-shaped and tapered towards the top. Stationary age structure of population is one in which birth and death rates change over a long period of time. It indicates that the birth rate is moderate and few people die off as they get older the population is stagnant to some extent the pyramid shows the decline in their birth rate this time was assisted by the fact that with for better living condition and health facilities children had a much better chance of survival.
4. Declining Population- Aging Population Pyramid:
- The declining population pyramid has a narrow base and tapered top showing low birth and death rates.
- The population growth in developed countries is usually zero or negative the pyramid has a narrow base resulting from the low birth rate and a broad bulge in the all the age groups which reflects the increase in life expectancy resulting from improvement in medical knowledge people live longer on an average and therefore has an aging population.