01 / 21

Population
Composition

Explore how age, sex, and demographic structure shape societies and influence policy decisions around the world.

AP Human Geography

What Is Population Composition?

Population composition describes the structure of a population broken down by characteristics such as age, sex, ethnicity, education, and income. Geographers use these breakdowns to understand how a society functions and what challenges it may face.

Core Demographic Measures

Sex Ratio
The number of males per 100 females in a population. A ratio above 100 means more males; below 100 means more females.
Dependency Ratio
Compares the non-working-age population (under 15 and over 64) to the working-age population (15 to 64).
Age Distribution
The proportional share of each age group within the total population, often visualized on a population pyramid.

Why Composition Matters

1
Economic planning: A youthful population needs schools and jobs; an aging population needs healthcare and pensions.
2
Migration policy: Countries with shrinking working-age cohorts may encourage immigration to fill labor gaps.
3
Social services: Dependency ratios reveal how many workers must support each non-worker, directly affecting tax burdens.
4
Political power: Age and sex structures influence voting patterns, policy priorities, and representation.

The Population Pyramid

A population pyramid is a back-to-back bar chart showing the distribution of a population by age (vertical axis) and sex (horizontal axis). Males are conventionally on the left, females on the right.

AGE 80+ 70-79 60-69 50-59 40-49 30-39 20-29 10-19 0-9 Males Females

Three Pyramid Shapes

Expansive
Wide base, narrow top. High birth rates and low life expectancy. Typical of Stage 1-2 DTM countries (e.g., Nigeria, Afghanistan).
Stationary
Roughly even bars throughout. Birth rates and death rates are balanced. Typical of Stage 3-4 DTM countries (e.g., U.S., France).
Constrictive
Narrow base, wider middle. Low birth rates, aging population. Typical of Stage 4-5 DTM countries (e.g., Japan, Germany).

The Dependency Ratio

The result tells you how many dependents (youth + elderly) exist for every 100 working-age people. A ratio of 70 means 70 dependents per 100 workers.

Youth Dependency
\(\frac{\text{Pop 0-14}}{\text{Pop 15-64}} \times 100\). High in developing countries with large young cohorts.
Elderly Dependency
\(\frac{\text{Pop 65+}}{\text{Pop 15-64}} \times 100\). High in developed countries with aging populations.

The Sex Ratio

Globally the sex ratio at birth is about 105 males per 100 females. But the ratio shifts with age because females tend to have higher life expectancy. Cultural practices, migration, and conflict also affect it.

1
Ratio > 100: More males than females (common in Gulf states due to male labor migration).
2
Ratio < 100: More females than males (common in aging European countries due to female longevity).

Youth vs. Elderly Dependency

Youth Dependency Elderly Dependency
Age group 0 to 14 65+
Typical where? Sub-Saharan Africa, South Asia Europe, Japan, South Korea
Policy needs Schools, pediatric care, jobs Pensions, geriatric care, housing
DTM stage Stage 1-2 Stage 4-5
Economic effect Large future labor force if educated Shrinking labor force, higher taxes

How to Read a Population Pyramid

1
Identify the shape: Is the base wide (expansive), even (stationary), or narrow (constrictive)?
2
Check for bulges or indentations: A bulge in the 20-34 range may indicate a baby boom generation or heavy in-migration of workers.
3
Compare male vs. female bars: Significant differences suggest sex-selective migration, conflict losses, or cultural practices.
4
Estimate dependency ratios: Visually compare the top + bottom thirds (dependents) to the middle third (workers).
5
Link to DTM stage: The shape correlates directly with where a country sits on the Demographic Transition Model.

Example: Calculating Dependency Ratio

Country X has: Population 0-14: 30 million, Population 15-64: 60 million, Population 65+: 10 million.

This means there are approximately 67 dependents for every 100 working-age people. This is a moderately high ratio, suggesting significant social service demands.

Example: Interpreting Sex Ratio

Qatar has approximately 2.7 million males and 0.8 million females.

A sex ratio of 337.5 means there are roughly 3.4 males for every female. This extreme imbalance results from massive labor in-migration of young male workers in the construction and petroleum industries.

Example: Reading Japan's Pyramid

80+ 70-79 60-69 50-59 40-49 30-39 20-29 10-19 0-9 Japan: Constrictive Pyramid

The Demographic Dividend

When a country transitions from high birth rates to lower birth rates, the working-age share temporarily bulges. If these workers are educated and employed, the country experiences accelerated economic growth: the demographic dividend.

High Birth Rate Many young dependents Dividend Window Large workforce, few dependents Aging Society Many elderly dependents Time Stage 2 Stage 2-3 Stage 4-5

Common Mistakes

✕ Confusing Ratio Direction
The dependency ratio compares dependents to workers, not workers to dependents. A higher number means more burden on workers.
✕ Ignoring Context for Sex Ratio
A high sex ratio does not always mean sex-selective practices. In Gulf states, it is driven by labor migration, not cultural norms.
✕ Equating Shape with Wealth
A constrictive pyramid does not always mean "rich." Some countries have low birth rates due to economic hardship, not prosperity (e.g., post-Soviet states).

Summary of Key Concepts

Concept Definition AP Connection
Population Pyramid Age-sex distribution chart Visualize DTM stages
Dependency Ratio Dependents per 100 workers Economic planning, policy
Sex Ratio Males per 100 females Migration, cultural practices
Demographic Dividend Growth from large workforce share Development, investment link
Expansive Pyramid Wide base, rapid growth Stage 1-2, youth bulge
Constrictive Pyramid Narrow base, aging Stage 4-5, population decline

Question 1 of 5

A country has 25 million people aged 0-14, 50 million aged 15-64, and 25 million aged 65+. What is its total dependency ratio?

Question 2 of 5

An expansive population pyramid is most characteristic of a country in which stage of the Demographic Transition Model?

Question 3 of 5

Qatar has a sex ratio of approximately 338. Which factor best explains this extreme imbalance?

Question 4 of 5

A country experiencing a demographic dividend would most likely show a population pyramid with which characteristic?

Question 5 of 5

Which statement about the elderly dependency ratio is most accurate?