2.4 Population Composition

Population Pyramids

A population pyramid graphs age and sex structure of a country, with age cohorts on the y-axis and percent/number of males and females on either side of the x-axis. Shape reveals stage of the demographic transition model (DTM): a wide base means high birth rates (Stage 2), a rectangular shape means low birth/death rates (Stage 4-5).

Dependency Ratio & Sex Ratio

The dependency ratio compares the number of economically dependent people (under 15, over 64) to the working-age population (15-64); a high ratio strains resources. The sex ratio compares males to females in a population, affected by factors like war, labor migration, or cultural preferences such as son preference.

Cohorts and Composition Uses

A cohort is a group of people born in the same time period, tracked as they age through a population pyramid. Analyzing population composition (age, sex, and other traits) helps planners predict future needs for schools, healthcare, jobs, and pensions.

Key terms

Population pyramid

A graph showing the age and sex composition of a population, used to infer stage of the DTM.

Dependency ratio

Ratio of dependents (under 15, over 64) to the working-age population (15-64).

Sex ratio

The relative number of males to females in a population, affected by migration, war, or cultural factors.

Cohort

A group of people born within the same time period, tracked as they age together.

Population composition

The structure of a population based on traits like age, sex, ethnicity, or occupation, used for planning resources.

Try an AP-style question

This indicates…

1. low fertility
2. an aging population
3. zero growth
4. high birth rates