The Demographic Transition Model (SACE Stage 2 Geography Population Change)
“Explain the stages of the demographic transition model, analyse how birth and death rates change through development, and evaluate the model's usefulness and limits.”
The demographic transition model (DTM) describes how a country's birth and death rates change as it develops, moving through stages from high birth and death rates to low birth and death rates. SACE answers must explain each stage, analyse why birth and death rates fall at different times and what that does to population growth and structure, and evaluate how useful the model is and where it breaks down, using country examples at each stage.
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What this dot point is asking
This dot point gives the central model for Population Change. The key geographical skill is using the DTM as a tool to explain and predict population patterns, while recognising it is a generalisation rather than a law.
The stages of the model
The DTM is usually shown with four or five stages, tracking birth rate, death rate and total population over time.
- Stage 1 (high stationary): high birth and death rates, so population is low and stable. No country sits clearly here today; it describes pre-industrial societies.
- Stage 2 (early expanding): death rates fall sharply through better food, sanitation and health care, while birth rates stay high, so population grows rapidly. Many of the least developed countries, such as parts of sub-Saharan Africa, are here.
- Stage 3 (late expanding): birth rates begin to fall as education, urbanisation, contraception and the changing role of women take effect, so growth slows. Many middle-income countries are in this stage.
- Stage 4 (low stationary): low birth and death rates give a stable, often large population. Most high-income countries, including Australia, are here.
- Stage 5 (decline): birth rates fall below death rates, so population shrinks and ages. Japan and several European countries fit this stage.
The defining feature of the model is the time lag: death rates drop quickly in Stage 2 because health and food improve fast, but birth rates stay high because having many children remains culturally and economically embedded. This gap between falling deaths and still-high births is what produces the population explosion of Stage 2. Explaining the lag, not just naming the stages, is what examiners reward.
Linking the model to population structure
Each stage has a characteristic population pyramid. Stage 2 shows a wide base of children and rapid growth; Stage 4 shows straighter sides; and Stage 5 shows a narrow base and a heavy top of older people. Being able to match a pyramid shape to a DTM stage, and explain the link, connects this dot point to the skills tested in the e-exam.
Why birth and death rates change
Death rates fall with improved nutrition, clean water, sanitation, vaccination and medical care. Birth rates fall later for social and economic reasons: girls' education, women working outside the home, urban living that makes large families costly, lower infant mortality (so families have fewer children expecting them to survive) and access to contraception. These drivers connect population change to development and to the social and economic systems of Topic 2.
Evaluating the model
The DTM is a powerful framework, but evaluation must note its limits.
- It is based on the historical experience of Europe and may not fit every country's path.
- It does not include migration, which strongly shapes growth in countries such as Australia.
- It assumes development always lowers birth rates, but cultural and religious factors can keep them high.
- Some countries move through stages far faster than the European originals, helped by imported medicine and technology.
- Stage 5 (decline) was added later because the original model did not anticipate sustained below-replacement fertility.
Do not just describe the four or five stages as a list. The dot point asks you to explain why death rates fall before birth rates, link each stage to population structure and growth, and evaluate the model's usefulness and limits, including its omission of migration. Treating the DTM as a fixed prediction rather than a generalisation is the error examiners watch for.
Questions often supply data and ask you to place a country in the model. Work it in steps.
Step 1: read the birth and death rates
Note the crude birth rate and death rate from the data, for example a birth rate of 38 and death rate of 10 per 1000.
Step 2: calculate natural increase
Natural increase is birth rate minus death rate, here per 1000, or , signalling rapid growth.
Step 3: assign the stage
High births with sharply fallen deaths and fast growth place the country in Stage 2; low births and deaths place it in Stage 4. Justify with the figures.
Step 4: link to structure and explain
Match the stage to a pyramid shape (wide base for Stage 2) and explain the time lag between falling deaths and births. Justifying the stage with data and the lag is what the marks reward.
Linking it together
A complete response explains the stages of the DTM, analyses the time lag between falling death and birth rates and its effect on growth and structure, links stages to population pyramids, and evaluates the model with country examples and acknowledged limits. That structure matches the geographical skills and applications criteria the SACE Board assesses.
Exam-style questions
Questions in the style of SACE Board exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
SACE 2023-style4 marksConsider the total fertility rates for 2015-20. Explain the variation in total fertility rates between high-income and low-income countries. Refer to social and economic factors in your response.Show worked answer →
Four marks for an "explain" question, so give causes (not just description) and cover both social and economic factors, linking each to higher or lower fertility.
Low-income countries have higher fertility because:
Social: lower female education and weaker access to contraception, earlier marriage, higher infant mortality (so families have more children to ensure some survive) and cultural or religious value placed on large families.
Economic: children provide farm labour and old-age security where there are few pensions, and limited urbanisation keeps the cost of raising children low.
High-income countries have lower fertility because:
Social: high female education and workforce participation, widespread contraception and later childbearing.
Economic: high cost of raising and educating children, urban living and reliance on pensions rather than children for support.
This mirrors the demographic transition model, where development drives falling birth rates.
Practise this
Sources & how we know this
- Stage 2 Geography subject outline (2025 onwards) — SACE Board
- Stage 2 Geography: external assessment — SACE Board