Population pyramids: Are a way of displaying the age / sex structure of a population. We can analyse it to predict the future and plan accordingly.
Dependency ratios: This is a ratio that compares the percentage of population available for work (15-64) and those economically inactive.
You can work it out: (All children 14 and under plus those aged 65 and over) divided by (number of adults aged 15-64).
The higher the ratio the more potential problems for the future.
Population structures: This is the age/sex balance that exists.
This is very closely linked to the demographic transition model and migration. You could be asked to talk about the population structure of an area and the implications of that structure for the future. In English, what is the percentage of males and females, how old are they and why does it matter.
The usual way to show this is with a population pyramid. This is simply a combination bar graph showing the percentage of males at different ages and the percentage of females at different ages. It can however tell us a lot about a country and its development.
Pyramid 1: Here the base is very wide indicating a very high birth rate. The width drops off very quickly. This means people must be dying. Very few reach old age. Few countries are still in this stage today but some rainforest populations would display this pattern.
Implications: Clear need for investment into water supplies, health care, food supplies and housing to reduce death rates.
Pyramid 2: Still a large base so high birth rate but also a wider and taller pyramid as more people are living to older ages. This is stage two of the demographic transition model and includes many countries in Africa such as Kenya.
Implication: Probable need to invest in education about family planning to reduce birth rate. Possibly indicates that women are undervalued in society so this could be tackled.
Pyramid 3: Note the more 'domed' shape. It means many people are living to older ages as quality of life improves. There are also proportionately fewer births. This is stage three of the demographic transition model. Chile would be a good example.
Implication: As the population becomes increasingly older there may be a need to invest in facilities and services for them. Still a need for continued investment in family planning.
Pyramid 4: Very small base due to the very low birth rates and death rates displayed in the wide top. This would be representative of Australia that has recently come through stage three of the demographic transition model.
Implication: Should the situation continue there are serious implications about providing for the elderly population (increasing cost of health care, state pensions) especially as the working population becomes proportionally smaller. This is a major concern in much of the developed world.
Population pyramids can also be influenced by:
Migration: Likelihood of extra young males as these are likely to migrate.
Famines: Clear drops in population especially among the very young as these are most likely to suffer.
War: Clear drop off in male populations of fighting age.
Make sure you can read data from a pyramid - try the one in the questions section.