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Unlock This CourseTwo countries can have the same total population but be very different places. One may be full of children and teenagers. The other may have lots of grandparents. Population structure is the make-up of a population by age and sex. It is shown on a population pyramid, also called an age-sex pyramid. The demographic transition model showed how birth and death rates change over time. A pyramid shows the result: who actually lives in the country now.
Key terms:
Every pyramid has the same layout:
Then look at the overall shape. The base shows the youngest people. The top shows the oldest. A bulge is a bar that sticks out more than the ones around it. An indent is a bar that is shorter than the ones around it.
The spec names two factors: natural increase and net migration.
A high birth rate gives a wide base, because there are lots of children. A longer life expectancy gives a wider top, because more people live to old age. A low birth rate gives a narrow base. A time when many people died, for example from disease or conflict, leaves an indent in the pyramid.
Migrants are mostly young adults looking for work. A country with high net migration gets a bulge in the working ages, roughly 20 to 39. If most migrants are men, the male bars are longer. Qatar and the United Arab Emirates have many more men than women because of migrant workers. A country that people leave gets an indent in those ages.
Remember that natural increase is the birth rate minus the death rate, and net migration is the difference between the number of people moving in and the number moving out.
| Shape | What it looks like | Typical country | Why |
|---|---|---|---|
| Wide-based, triangular | Very wide base, sides slope sharply inwards, narrow top | LICs, such as Niger | High birth rate and a fairly short life expectancy |
| Straight-sided, almost rectangular | Base only a little narrower than the middle, bars fall away slowly with age | MICs and many HICs | Birth rate has fallen and most people now survive to older ages |
| Narrow base, wide top | Narrow base, widest in the middle or upper ages | HICs with very low birth rates, such as Japan | Very low birth rate and a high life expectancy |
As a country develops, its pyramid usually changes from the first shape towards the third. The next lesson, Youthful and Ageing Populations, looks at the causes and impacts of the two ends of this range.
You may be given a table and asked to complete or draw a pyramid. Here is made-up data for Country Q, as a percentage of the total population.
| Age group | Males (%) | Females (%) |
|---|---|---|
| 60+ | 4 | 6 |
| 45-59 | 7 | 9 |
| 30-44 | 10 | 10 |
| 15-29 | 12 | 12 |
| 0-14 | 15 | 15 |
Country Q has a base wider than its top. The 60+ bar is only 4% for males and 6% for females, so there are few old people. Women live longer than men on average, which is why the female bar at the top is longer.
Dependants cannot earn much, so the working population has to support them through taxes and in families. The dependency ratio shows how big that task is:
Dependency ratio = (number aged 0-14 + number aged 65 and over) ÷ (number aged 15-64) × 100
Country Z has 3.0 million people aged 0-14, 6.0 million aged 15-64 and 1.0 million aged 65 and over.
So there are about 67 dependants for every 100 people of working age.
A high ratio means each worker supports more people. A low ratio means each worker supports fewer.
Fig. 1.1 shows made-up data for Country R, as a percentage of its total population.
| Age group | Males (%) | Females (%) |
|---|---|---|
| 60+ | 2 | 3 |
| 45-59 | 6 | 7 |
| 30-44 | 10 | 10 |
| 15-29 | 14 | 13 |
| 0-14 | 18 | 17 |
(a) Identify the age group with the highest percentage of males. [1 mark]
(b) Calculate the percentage of the total population aged 0-14. [1 mark]
(c) Describe the shape of the population pyramid for Country R. [2 marks]
(d) Explain why Country R has a wide base. [3 marks]
(e) Explain how natural increase and net migration can change a country's population structure. [6 marks]
(a) 0-14 (1).
(b) 18 + 17 = 35% (1).
(c) The pyramid has a very wide base, with 35% of the population under 15 (1). The bars get shorter with each older age group, so it is narrow at the top, with only 5% aged 60 and over (1).
(d) The birth rate is high, so many babies are born each year (1). Many of these children grow up and have children of their own, so the base stays wide (1). A reason for the high birth rate, such as high infant mortality so parents have more children, or little access to family planning (1).
(e) Level 3 answer: Natural increase is the birth rate minus the death rate. A high birth rate means many children and a wide base. A low birth rate gives a narrow base. A longer life expectancy means more people reach old age, so the top of the pyramid gets wider. Net migration also changes the structure. Migrants are mostly young adults, so a country with high immigration gets a bulge in the working ages, such as 20 to 39. If more men than women migrate, as in Qatar, the male bars are longer. A country with high emigration gets an indent in those ages. In short, natural increase mainly changes the very young and very old ends, while net migration mainly changes the working ages and the balance of males and females.
In a 'Describe' question use numbers from the table. In an 'Explain' question, say what the shape shows and then give the reason for it, such as 'high birth rate, so a wide base'.