Age structures and demographic events (cont.)
The interaction between mortality and the age structure
Mortality removes individuals from a population. Once individuals have been born the mortality level and schedule determines how many of them remain at each age.
The age structure of a population will not change if it is just the level of mortality which changes as each age group will reduce by the same amount (and so will proportionally remain the same). However in reality, when mortality changes there is usually a greater proportional change in certain age groups.
- When mortality declines in high mortality populations, there is a greater proportional decline in the youngest age groups. Counter-intuitively, this means that initial mortality decline causes a population to become younger even though on average people are living longer. This is because the number of infants and children remaining in the population is increased.
- In low mortality populations, mortality declines are usually concentrated in older age groups, causing the relative share of older age groups to increase and the population to age.
Death rates also vary between men and women. At any given age, the death rate is higher in men (apart from in areas with high maternal mortality). This has the effect of reducing the male population as age increases, and gives an imbalanced sex structure at older ages. This will be covered later in the session.
As the risk of death is strongly related to age, the age structure determines the number of deaths which will occur. Risk of death increases with age, and so a population with a greater number of people in the older age groups will experience more deaths than a population with a smaller proportion of people in the older age groups, even if the underlying mortality rate is higher in the second population.