The big idea: A population pyramid shows a country's age and sex structure.
- Males are on the left, females on the right. - Age groups are stacked, youngest at the bottom. - Bar length = the share of people in that group.
Read the bars (values) and the overall shape — both are tested.
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Key terms
- Age structure — how the population is split between young, working-age and old.
- Dependants — under-15s and over-65s, who rely on the working-age (15–64) population.
- Sex ratio — the balance of males to females (often per 100 females).
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The shape tells the story. Compare the youthful pyramid above with this ageing one — the base is narrow and the top is wide.
Few children, many older people — a slow-growing, ageing population.
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Shape → what it tells you
| Shape | What it means |
|---|---|
| Wide base, narrows quickly | Youthful — high birth rate, fast growth (often lower-income) |
| Narrow base, wide middle/top | Ageing — low birth rate, more elderly (often higher-income) |
| A bulge in one band | A past baby boom, or migration of working-age people |
| Longer female side at the top | Women tend to live longer — common in older age groups |
The demographic transition model (DTM): The DTM shows how a country's birth rate, death rate and natural increase change over time as it develops. Each stage gives a different population pyramid and a different dependency ratio.
Stage by stage: rates, pyramid and real countries
| Stage | Birth and death rates | Pyramid shape | Real countries today |
|---|---|---|---|
| 1 High stationary | both high, so little growth | wide base, very narrow top | no country now (a few isolated groups) |
| 2 Early expanding | death rate falls, birth rate stays high: fast growth | very wide base, concave sides | Niger, Chad |
| 3 Late expanding | birth rate falls, growth slows | base narrowing, wider middle | India, Kenya |
| 4 Low stationary | both low, growth near zero | straight sides, beehive | USA, UK |
| 5 Declining | death rate above birth rate | narrow base, wide top | Japan, Italy |
Niger (stage 2)
- Fertility about 6-7 children per woman
- Median age about 15
- Very high youth dependency
- Population growing about 3-4% a year
Japan (stage 5)
- Fertility about 1.2-1.3
- Median age about 49
- Very high elderly dependency
- Deaths have outnumbered births since the late 2000s, so the population is shrinking
Limits of the DTM
- Built on Western Europe — today's lower-income countries move through it much faster, because medicine and contraception arrive from outside.
- Ignores migration — the Gulf states or the UK can grow even with low natural increase.
- Not a forecast — a country can stall in stage 3 if girls' schooling or jobs do not improve, and the model has no stage for a recovery in births.
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Natural increase: The rate of natural increase is births minus deaths (per 1000 people per year), ignoring migration.
Positive → the population grows from within; negative → it shrinks.
Outline what is meant by the rate of natural increase.
Model answer plan
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Median age and the dependency ratio
- Median age — the age that splits the population in half: half are younger, half are older. A youthful country has a low median age (under 20); an ageing one a high median age (over 40).
- The median age falls when the birth rate rises, when young migrants arrive, or when more older people die; it rises when births fall and people live longer.
- Dependency ratio = (people aged 0-14 + people aged 65+) ÷ people aged 15-64 × 100.
- A high ratio means each worker supports more dependants: youthful countries have many young dependants, ageing countries many elderly ones.
Explain how migration can leave a place with an unbalanced ratio of males to females.
Model answer plan
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How this is tested: A population pyramid (or a median-age line graph) is the figure you read most here.
The low-mark commands
Identify [1]
The largest age group.
State or Estimate [1]
A value off the axis.
Describe [2]
The shape of the figure.
The low-mark commands stay close to the data.
Read first: Read the axis units first and always quote the figures you see.
Use this pyramid to answer the question below.
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IB-style question — read the pyramid
Using the population pyramid above: (a) identify the age group with the most people [1]; (b) estimate the percentage aged 0–14 [1]; (c) describe the shape of the pyramid [2].
How to answer each part
- (a) Identify the largest group. Find the longest pair of bars — the 0–14 group has the longest bars, so it has the most people.
- (b) Estimate 0–14. Add the male and female bars for 0–14 (≈16% + ≈15%) → about 31%.
- (c) Describe the shape. It has a wide base that narrows quickly toward the top — a youthful population with a high birth rate.
Final answer
(a) the 0–14 group; (b) ≈ 31%; (c) wide base narrowing to a small top → youthful, high birth rate.
A median-age line graph: the second figure type this micro is tested with.
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Data-response marks: Identify/State = read it straight off. Estimate = give a sensible figure from the axis. Describe = report the pattern (shape + figures), no reasons.