Topic 2.5 Notes – The Demographic Transition Model

What the Demographic Transition Model Is

The DTM is a model that shows how crude birth rate, crude death rate, and natural increase usually change as a country develops. The basic pattern stays the same:

• high birth rates + high death rates
• death rate drops first
• birth rate drops later
• both end up low

That middle period matters most because population grows fastest there. Births stay high while deaths fall, so the gap between them gets wide before it narrows.

Variables to know

• CBR = births per 1,000 people
• CDR = deaths per 1,000 people
• RNI = population growth from births and deaths only

$$\text{RNI} = \frac{\text{CBR} - \text{CDR}}{10}$$

• If CBR is 30 and CDR is 10, RNI is 2%.
• Natural increase does not include migration. A country can still grow if lots of people move in.

How to read the graph

In the graph, focus on the blue birth-rate line, the orange death-rate line, and the yellow total-population curve.

Demographic Transition Model graph

• x-axis shows time or development
• y-axis shows birth and death rates
• the distance between the birth-rate and death-rate lines shows natural increase
• the total population curve rises slowly, then quickly, then slows, and may level off or fall

Exam trap: a falling birth rate does not mean population decline. If births are still above deaths, population is still growing.

The Five Stages of the DTM

Stage 1

High stationary means high CBR and high CDR, both bouncing around. Growth stays low over the long run.

• Causes of high death rates include disease, famine, poor sanitation, and weak food supply.
• Causes of high birth rates include little contraception and the need for child labor.
• No whole countries are usually placed in Stage 1 today.

Stage 2

Early expanding starts when the CDR drops fast but the CBR stays high. This creates the fastest natural increase.

• Death rates fall because of clean water, sanitation, vaccines, public health, and more reliable food.
• This is the classic population explosion stage.
• A common example is parts of sub-Saharan Africa.

Stage 3

Late expanding means the CBR starts falling while the CDR stays low. Population still grows, just more slowly.

• Urbanization makes children less useful as labor.
• Contraception becomes more available.
• Women’s education and employment rise.
• Lower infant mortality reduces pressure to have many children.
• Population momentum means growth can continue because a large young population is entering childbearing years.

Stage 4

Low stationary has low CBR and low CDR. Growth is slow or close to zero.

• Often-used examples are the United States, Canada, and much of Western Europe.
• Total population can still rise because of immigration.

Stage 5

Declining means the CBR falls below the CDR.

• RNI becomes negative, so there is natural decrease.
• This is tied to below-replacement fertility, about 2.1 children per woman.
• Common examples are Japan, Germany, Italy, and China in recent years.
• Aging can push up the CDR even with great health care.

Population Pyramids and Stage Clues

Population pyramids help because they show the effects of fertility and mortality over time. The basic shapes at the top of the figure match the stage patterns, and the Angola and Japan examples show what those patterns look like in real populations.

Population pyramid types and examples

• Stage 1 has a broad base, steep narrowing, and very few elderly people.
• Stage 2 has a very wide base and huge child cohorts.
• Stage 3 has a narrowing base and a wider working-age middle.
• Stage 4 looks more column-shaped.
• Stage 5 has a narrow base and a top-heavy or urn-shaped look.

Be careful with bulges and gaps. Migration, war, epidemics, and baby booms can distort the shape, so use pyramids as evidence, not proof by themselves.

The Epidemiological Transition

The epidemiological transition explains why death rates change. The DTM shows what happens to mortality. This model explains the causes of death behind it.

• Stage 1 pestilence and famine includes infectious disease, malnutrition, childbirth risks, and environmental hazards.
• Stage 2 receding pandemics comes from sanitation, safe water, better nutrition, and vaccination. This drives the DTM death-rate drop.
• Stage 3 degenerative and human-created diseases includes heart disease, cancer, diabetes, pollution, smoking, and accidents.
• Stage 4 delayed degenerative diseases means people still face chronic disease, but medicine delays death and increases life expectancy.
• Proposed Stage 5 involves reemerging infectious disease such as drug-resistant tuberculosis, malaria, and COVID-19. This does not mean countries automatically move backward in the DTM.

Why the Model Matters and Where It Breaks Down

The DTM is useful for comparing countries, explaining population growth, and linking development to age structure, urbanization, and dependency.

Its limits matter too:

• It was based mostly on Europe and North America.
• It gives no fixed timeline.
• It does not handle migration well.
• War, pandemics, and disasters can disrupt the pattern.
• National averages can hide regional differences.
• Stage 5 is debated.

On AP questions, the best move is to use dated CBR, CDR, RNI, and pyramid evidence together, then mention migration or another complicating factor if it matters.