Population Composition & Modelling (HL IB ESS OLD COURSE - IGNORE)

Revision Note

Human Population Models

Age-sex pyramids

  • The composition of human populations can be modelled and compared using age–sex pyramids

    • These are sometimes referred to as population pyramids, age-gender pyramids or age structure diagrams

  • An age–sex pyramid is a graphical representation of a population's age and sex structure

    • It displays the percentage or number of individuals in each age group and gender within a given population

    • They typically show data for a particular country or region

  • The age–sex pyramid is usually represented as a horizontal bar graph

    • The age groups are displayed along the vertical axis

    • The percentage or number of individuals in each age group is displayed along the horizontal axis

    • The left side of the graph displays the male population

    • The right side shows the female population

  • The shape of the age–sex pyramid can provide insights into the demographic characteristics of a population

    • For example, a pyramid with a broad base and a narrow top indicates a young population with high fertility rates and low life expectancy

    • Whereas a pyramid with a narrow base and a broad top indicates an ageing population with low fertility rates and high life expectancy

Diagram showing an example of a population pyramid
An example of a population pyramid
  • Age–sex pyramids are used by policymakers and economists to:

    • Understand population trends

    • Forecast future population growth

    • Plan for social and economic policies

  • They are also used in fields such as public health, education and social welfare to plan for the needs of specific age groups within a population

    • This means that governments can estimate and plan for spending

  • An age–sex pyramid can be used to identify the following groups:

    • Young dependents

    • Old dependents

    • Economically active (working population)

Population structures of LICs and HICs

Diagram showing an age–sex pyramid for Niger
Age–sex pyramid for Niger
  • Low-income countries (LICs) like Niger typically have a concave pyramid shape

  • This indicates:

    • High birth rate

    • Low life expectancy

    • High death rate

    • High infant mortality rate

    • Young dependent population dominates

Diagram showing an age–sex pyramid for Nepal
Age–sex pyramid for Nepal
  • More developed LICs like Nepal typically have a pyramid shape with a taller base, like the one shown above

  • This indicates:

    • Decreasing birth rate 

    • Increasing life expectancy

    • Decreasing death rate

    • Decreasing infant mortality

    • Decreasing young dependents and increasing economically active population

Diagram of an age–sex pyramid for USA
Age–sex pyramid for USA
  • High-income countries (HICs) such as the USA typically have a column shape

  • This indicates:

    • Low birth rate 

    • High life expectancy

    • Low death rate 

    • Low infant mortality

    • Large working age population

Worked Example

An age–sex pyramid is shown below.

What does the shape of the pyramid tell you about the population structure of the country?

5YVJ9dns_population-pyramid-italy-worked-example

Answer

  • The narrow base means a low birth rate

  • A low birth rate means a low number of young dependents

  • A reasonably broad top means high life expectancy

  • The majority of the population is between 40 and 60

  • This means there will be a large number of elderly dependents in the future

Worked Example

The figure below shows age–sex pyramids for Mexico in 1980 and 2010.

Describe the changes in Mexico's population structure between 1980 and 2010.

002acb54-af1b-48cb-8a3b-4451f2bcaf32

Answer

  • In 2010 there are:

    • More economically active / working / 15-64 year-olds

    • More elderly / old dependents / 65+ year-olds

    • More young dependents in total / bands up to 19 become more even

Examiner Tips and Tricks

Remember—when interpreting an age–sex pyramid, you need to look at four key areas:

  • Younger population - is the birth rate high or low?

  • Working population - are there enough people of working age to support the young and old dependents?

  • Elderly population - is it large or small? (if it is large, then life expectancy is high)

  • Male/female split - are there any noticeable differences between the numbers of males and females?

Demographic transition model (DTM)

  • The DTM is a model that shows how a population transitions over time:

    • From a pre-industrial stage, with high crude birth rates and high crude death rates

    • To an economically advanced stage, with low or declining crude birth rates and low crude death rates

  • The DTM illustrates five generalised stages that countries pass through as they develop

  • It shows how the birth and death rates change and how this affects the overall population of the country

Demographic Transition Model graph showing birth and death rates per 1000 people across five stages over time. Birth rates (red), death rates (green), and total population (purple) vary by stage.
The Demographic Transition Model

Stage 1

  • The total population is low 

  • High birth rates due to lack of contraception and family planning 

  • High death rates due to poor healthcare, poor diet and famine

  • High infant mortality, which leads people to have more children so that some children survive to adulthood

Stage 2

  • The total population starts to rise rapidly

  • Birth rates remain high as people continue to have large families

  • Death rates decrease as a result of improved diets, better healthcare, lower infant mortality and increased access to clean water

Stage 3

  • The total population continues to increase but the rate of growth begins to slow

  • Birth rate begins to fall rapidly due to increased birth control, family planning, increased cost of raising children and low infant mortality rate 

  • Death rate still decreasing but at a slower rate as improvements in medicine, hygiene, diet and water quality continue

Stage 4

  • The total population is high and is increasing slowly 

  • Birth rate is low and fluctuating due to accessible birth control and the choice of having fewer children as well as delaying the age women start to have children

  • Death rate is low and fluctuating

Stage 5

  • The total population starts to slowly decline as the death rate exceeds the birth rate 

  • Birth rate is low and slowly decreasing

  • Death rate is low and fluctuating

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