Population Composition
Introduced| English | Meaning |
|---|---|
| population composition/ˌpɒpjʊˈleɪʃn ˌkɒmpəˈzɪʃn/ | The make-up of a population by age and sex. |
| population pyramid/ˌpɒpjʊˈleɪʃn ˈpɪrəmɪd/ | A diagram showing a population's age and sex structure in horizontal bars. |
| dependency ratio/dɪˈpendənsi ˈreɪʃɪəʊ/ | The size of younger and older age groups relative to the working-age group, commonly comparing ages under 15 and 65 or over with ages 15 to 64. |
The make-up of a population
- Population composition 人口构成 is the make-up of a population by age and sex.
- It is shown on a population pyramid 人口金字塔 — back-to-back bar charts.
- The shape of the pyramid tells you the story of a country.
The make-up of a population by age and sex is population ____.
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Population composition is shown on a population pyramid.
Reading the shape
- A wide base = many young people = high birth rate = rapid growth.
- Straight sides = slow, stable growth.
- A narrow base = few young people = an ageing, shrinking population.
Schematic age structures, not forecasts: age rises upwards; bar width represents relative cohort size
What does the pyramid shape mean?
Sort each pyramid shape by what it tells you about growth.
A population pyramid with a very wide base shows...
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A wide base = many young people = high birth rate = rapid growth.
Match each pyramid shape to its meaning.
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Wide = growing; straight = stable; narrow = ageing.
The dependency ratio
- The dependency ratio 抚养比 compares dependents to working-age people.
- Dependents are the young (under 15) and the old (over 64).
- A high ratio strains the workers who must support everyone else.
The dependency ratio counts the young and the old as dependents.
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Dependents = under 15 and over 64; the working-age support them.
A country has 30 million dependents and 60 million working-age people. What is the dependency ratio, as dependents per 100 workers?
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30/60 = 0.5, so 50 dependents per 100 workers.
A wide base is not always good. It means rapid growth, which can strain schools, jobs, food, and services. A narrow base is not simply "bad" either — it means an ageing society with its own challenges. Read the shape, do not judge it.
Niger has a wide-based pyramid: about half its people are children. Japan has a narrow-based, top-heavy pyramid: many elderly, few children. Same chart type, opposite stories — one faces rapid growth, the other rapid ageing.
Population composition (age and sex) is shown on a population pyramid. A wide base = rapid growth; straight sides = stable; narrow base = ageing. The dependency ratio compares the young + old to working-age people.
Write from a dependency ratio of 25
- A country has 20 million dependents and 80 million working-age people.
- The lesson country has 30 million dependents and 60 million workers, a ratio of 50.
What is the dependency ratio per 100 workers?
Dependents per 100 working-age people is the dependency ratio.
What is this dependency ratio?
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20 is one quarter of 80, which is 25 per 100. Other options — 50 (the lesson ratio); 20 million (the dependent count).