Population Composition & Modelling (DP IB Environmental Systems & Societies (ESS))

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

• 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

• 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

• 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

• 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

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

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