IB Syllabus focus:
‘The DTM outlines stages as death then birth rates fall, producing growth, stabilization, and possible decline; characteristic age–sex pyramids align with stages.’
The Demographic Transition Model (DTM) is a framework used to describe how populations change over time as societies develop. It links birth rates, death rates, and growth.
The Concept of the Demographic Transition Model
The DTM is a theoretical model that outlines population changes through distinct stages of social and economic development. It shows how death rates fall first, followed later by birth rates, producing a temporary surge in population growth before eventual stabilisation or decline. A key feature of the model is the relationship between population dynamics and age–sex pyramids, which illustrate population structure.
A labelled demographic transition diagram showing birth rate and death rate trajectories across stages, with the widening and narrowing gap indicating population growth phases. This directly supports the idea that mortality declines precede fertility declines and that growth later stabilises or reverses. Source.
The Stages of the Demographic Transition Model
Stage 1: High Stationary
Both birth rates and death rates are high and fluctuating.
Population growth is minimal due to balance between inputs and outputs.
Societies are typically pre-industrial, reliant on subsistence farming, and prone to famine, disease, and high infant mortality.
Age–sex pyramid is broad-based and steep-sided, indicating a large proportion of children.
Infant Mortality Rate: The number of infant deaths (under age 1) per 1,000 live births in a given year.
Stage 1 is largely theoretical in modern times, as almost all societies have transitioned beyond this phase.
Stage 2: Early Expanding
Death rates fall rapidly due to improvements in food supply, sanitation, and basic healthcare.
Birth rates remain high, leading to rapid population growth.
Common in societies at the start of industrialisation.
Age–sex pyramid has a wide base and gradually expanding middle, reflecting high fertility and improving survival rates.
Stage 3: Late Expanding
Birth rates begin to decline due to changing social values, urbanisation, access to contraception, and improvements in women’s education and status.
Death rates continue to fall but more slowly.
Population growth slows as the gap between births and deaths narrows.
Age–sex pyramid shows a narrower base and expanding middle-aged cohorts.
Fertility Rate: The average number of children a woman is expected to have during her reproductive years.
Stage 3 illustrates the impact of indirect development policies such as investment in education and healthcare, which influence demographic change.
Stage 4: Low Stationary
Birth rates and death rates are both low.
Population growth stabilises at a low or zero growth rate.
Associated with highly industrialised or post-industrial societies.
Age–sex pyramid shows a rectangular shape, with a balanced distribution across age groups and lower dependency ratios.
Dependency Ratio: The proportion of dependents (young and elderly) compared to the working-age population, usually expressed as a percentage.
Stage 5: Declining? (Debated)
Not part of the original DTM but often included to describe current trends in some developed nations.
Birth rates fall below death rates, producing natural decrease.
Population begins to shrink and age rapidly, leading to social and economic challenges such as labour shortages and increased healthcare demands.
Age–sex pyramid becomes top-heavy, with a narrowing base and expanding elderly population.
Links Between the DTM and Age–Sex Pyramids
Age–sex pyramids provide a visual representation of population structure and are closely aligned with the DTM stages. Each stage has distinctive pyramid characteristics:
Stage 1: Very wide base, steeply tapering sides, high youth dependency.
Stage 2: Wide base, broadening lower middle, indicating rapid growth.
Stage 3: Narrower base, wider middle, reflecting declining fertility and ageing.
Stage 4: Almost rectangular, showing stability with balanced cohorts.
Stage 5: Narrow base, bulging top, indicating ageing and declining population.
These diagrams are essential tools for planners to understand dependency ratios, growth pressures, and future demographic needs.
A comparative panel of age–sex pyramid shapes for DTM Stages 1–5, from wide-base expansive structures to top-heavy forms with narrow bases. This visual supports interpretation of growth patterns and dependency through changing population structure across the transition. Source.
Criticisms and Limitations of the DTM
Although widely used, the DTM has limitations:
It is Eurocentric, based on Western historical experience, and may not fully apply to other regions.
Assumes all societies will pass through the same stages, but cultural, religious, political, and economic factors may lead to different outcomes.
Does not account for the impact of migration, which can alter population dynamics independent of birth and death rates.
The potential Stage 5 remains debated, as not all low-fertility countries follow the same patterns.
Importance of the DTM in Environmental Systems and Societies
The DTM is critical for understanding:
Population pressures on resources such as food, water, and energy.
Urbanisation trends and infrastructure demands.
Links between development policies and demographic change.
Planning for healthcare, education, housing, and employment based on shifting population structures.
The relationship between population change and sustainability, as rapidly growing populations place stress on ecosystems, while ageing populations present different challenges.
By examining the stages of demographic transition alongside age–sex pyramids, students can better appreciate how population growth, stabilisation, and decline shape societies and their interaction with the environment.
FAQ
Economic development typically drives societies from Stage 2 to Stage 3, as improved income levels reduce mortality and later influence fertility decisions.
As wealth increases:
Families invest more in education rather than large families.
Women enter the workforce, lowering birth rates.
Access to healthcare and nutrition extends life expectancy, pushing death rates down.
These shifts help explain why more developed nations stabilise at Stage 4 or move into Stage 5.
Stage 1 describes high, fluctuating birth and death rates seen in pre-industrial societies. Very few modern societies remain in this stage due to global improvements in medicine, sanitation, and food supply.
Anthropologists sometimes use the model to describe isolated indigenous groups, but in practice, almost all nations have moved beyond Stage 1.
Stage 3 is marked not just by falling birth rates but also by major social shifts:
Increased female education and employment opportunities.
Greater urbanisation, reducing reliance on large families for labour.
Widespread availability of contraception and family planning.
These factors combine to reshape cultural norms around family size.
Governments use DTM projections to allocate resources and anticipate challenges:
Stage 2–3 countries: Plan for rapid population growth, education, and job creation.
Stage 4–5 countries: Prepare for ageing populations, healthcare demands, and pension pressures.
By linking age–sex pyramids to DTM stages, policymakers can adapt strategies to demographic realities.
Although the DTM focuses on births and deaths, migration can significantly alter demographic patterns.
High immigration can counteract low fertility in Stage 4 or 5, slowing population decline.
Emigration from Stage 2 or 3 countries may reduce growth but increase dependency ratios.
This demonstrates why some critics argue the DTM oversimplifies population dynamics by excluding migration trends.
Practice Questions
Question 1 (2 marks)
State two key demographic changes that occur between Stage 2 and Stage 3 of the Demographic Transition Model (DTM).
Mark Scheme:
1 mark for identifying the decline in death rates that has already occurred in Stage 2.
1 mark for identifying the subsequent decline in birth rates that begins in Stage 3.
(Other valid answers: slowing of population growth, increasing life expectancy, reduced fertility.)
Question 2 (5 marks)
Explain how age–sex pyramids illustrate the different stages of the Demographic Transition Model (DTM).
Mark Scheme:
1 mark for stating that age–sex pyramids show population structure by age and gender.
1 mark for describing Stage 1: broad base, steep sides, high youth dependency.
1 mark for describing Stage 2: wide base, broadening lower middle, rapid growth.
1 mark for describing Stage 3: narrower base, wider middle-aged cohorts, slowing growth.
1 mark for describing Stage 4 or Stage 5: rectangular or top-heavy, indicating stability or ageing.
(Maximum 5 marks. Candidates may earn full marks through accurate descriptions of at least four different stages linked to pyramid shapes.)
