1. Population structure IGCSE Global Perspectives

2. The structure or composition of a population is the product of the process of fertility, mortality and migration. The most studied aspects of population structure are age and sex. Other aspects that can also be studied include race, language, religion, and social/occupational groups.

3. Population pyramids Age and sex structure is conventionally illustrated by the use of population pyramids. Pyramids can be used to portray either absolute or relative data. Absolute data shows the figures in thousands or millions while relative data shows the numbers involved in percentages. The letter is most frequently used as it allows for easier comparison of countries of different population sizes.

4. An annotated population pyramid

6. The dependency ratio The dependency ratio is the relationship between the working or economically active population and the non- working population. The dependency ratio for MDC is usually between 50 and 75. In contrast, LDC typically have ratios between 85 and 105. The youth dependency ratio is the ratio of the number of people under 15 to those 15-64 years of age. The elderly dependency ratio is the ratio of the number of people over 64 years to those 15-64 years of age.

8. Sex structure The sex ratio is the number of males per 1000 females in a population. Male births consistently exceed female births due to a combination of biological and social reasons. For example, more couples decide to complete their family on the birth of a boy than on the birth of a girl. In the UK 105 boys are born for every 100 girls. However, after birth the gap generally begins to narrow until eventually females outnumber males, as at every age male mortality is higher than female mortality. This process happens most rapidly in the poorest countries where infant mortality is markedly higher among males than females. Here the gap may be closed in less than a year. In the UK it is not until the 45-59 age group that females outnumber males. In the age group 85 and over females make up 74 per cent of the population.