Dependency Ratio & Population Momentum (HL) (DP IB Environmental Systems & Societies (ESS))

Dependency Ratio & Population Momentum

Dependency ratio

• Population structures and age-sex pyramids can be divided into three age-group categories

• These categories depend on level of economic activity:

  • Young dependents = from 0-14 years

    • They rely on their economically active parents to support them

    • High in countries with high fertility rates (e.g. Nigeria)

  • Economically active = from 15-64 years

    • They are the working population who earn income, pay taxes and contribute to the support of the young and elderly

  • Elderly dependents = from 65 years onwards

    • They are no longer economically active and so rely on support from the state and younger family members

    • High in countries with ageing populations (e.g. Japan)

• The dependency ratio shows the relationship between a the working population (people who are economically active or independent) and non-working population (people who are economically inactive or dependent)

  • In other words, the dependency ratio is a way to measure the amount that the young and elderly people in a population depend on the economically active people in that population

• A low dependency ratio means more workers relative to dependents

  • This supports economic growth

Dependency ratio = ((young dependents + old dependents) ÷ economically active) × 100

or

Population momentum

• Population momentum is the tendency for population growth to continue even after fertility rates decline

• Why it happens:

  • A large population of young people means more women will enter reproductive age in the future

  • This causes population growth even with low fertility rates

Key factors

• Age structure:

  • A youthful population leads to sustained growth over decades

    • E.g. countries like India have significant population momentum due to a large number of young people

• Declining fertility:

  • Growth slows gradually as smaller generations replace larger ones

    • E.g. after the one-child policy in China (1980-2016), fertility rates (TFR) dropped

    • Despite this, the population continued growing (more and more slowly) for decades before stabilising

Negative population momentum

• Negative population momentum can also occur

• This is when, despite an increase in TFR, the number of people of reproductive age has shrunk

  • This results in fewer people having children

  • E.g. Japan has relatively few women of reproductive age, so the population momentum is decreasing