The Demographic Transition Model and Development

Demographers use specific formulas to measure these changes:

• Natural Change (per 1,000): $BR - DR$
• Natural Increase Rate (as %): $\frac{BR - DR}{10}$
• Dependency Ratio: $\frac{(\% \text{under } 15 + \% \text{over } 65)}{\% \text{working age (15–64)}} \times 100$

Worked Example: Calculating Natural Increase Rate

A country has a birth rate of 20 per 1,000 and a death rate of 8 per 1,000. Calculate the natural increase rate as a percentage.

Step 1: Write down the formula.

• $\text{Natural Increase Rate} = \frac{BR - DR}{10}$

Step 2: Substitute the known values.

• $BR = 20$
• $DR = 8$
• $\text{Rate} = \frac{20 - 8}{10}$

Step 3: Calculate the final answer with units.

• $\text{Rate} = \frac{12}{10} = 1.2\%$

Stages 1 and 2: Pre-Industrial to LICs

The vast majority of human history was spent in Stage 1 of the DTM, yet today, not a single entire country remains there. In Stage 1 (High Fluctuating), both birth and death rates are extremely high and fluctuating (around 35–40 per 1,000) due to disease, famine, and no contraception. Natural change is virtually zero, keeping the total population low and stable. Today, this stage only applies to isolated groups, such as tribes in the Amazon rainforest.

Stage 2 (Early Expanding) is typical of Low-Income Countries (LICs) with a GNI per capita of $1,135 or less, such as Afghanistan and The Gambia. The birth rate remains high and steady, but the death rate falls rapidly to approximately 15–20 per 1,000. This widening gap triggers a "population explosion" with a very high rate of natural increase. A population pyramid for a Stage 2 country has a wide base (reflecting the high birth rate), a narrow apex (showing low life expectancy), and straighter sides than Stage 1.

Analysing the link to development, the death rate drops in Stage 2 because of investments in basic healthcare (like vaccinations for polio) and improved sanitation (safe water reduces cholera outbreaks). Birth rates stay high because children are economic assets for manual labour on farms (primary sector). Furthermore, a high Infant Mortality Rate (IMR) means families have "replacement" children to ensure some survive to adulthood.

Stage 3: The Shift to NEEs

When countries undergo rapid industrialisation, their populations transform just as quickly as their economies. Stage 3 (Late Expanding) features countries transitioning into Newly Emerging Economies (NEEs), such as India, Brazil, Nigeria, and Bangladesh.

In this stage, the birth rate finally falls rapidly (e.g., Bangladesh dropped from 7 children per woman in 1970 to around 2.1 today), while the death rate continues to decline slowly. Natural increase remains high, but the rate of growth begins to slow down.

This demographic shift correlates directly with economic development. As countries move from primary agriculture to secondary manufacturing, rapid urbanisation occurs. In cities, children become an economic liability rather than an asset. Simultaneously, improvements in female emancipation provide women with better education and career opportunities, leading to later marriage. Widespread access to family planning and a lower IMR further reduce the need for large families.

Stages 4 and 5: HICs and Declining Populations

In some advanced economies, the population is actually shrinking naturally, forcing them to rely heavily on migration. Stage 4 (Low Fluctuating) is typical of High-Income Countries (HICs) like the UK and USA. Both birth rates (10–13 per 1,000) and death rates (8–10 per 1,000) are low and fluctuating. Natural change is very slow, resulting in a high, stable total population. The population pyramid for a Stage 4 country takes on a "barrel" shape, with a narrow base and straight sides.

Stage 4 birth rates are driven down by the high cost of childcare, women prioritizing careers, and the widespread use of birth control. For example, in the UK, the average age for a first-time mother is 30.9 years, and the fertility rate is 1.56. This is well below the Replacement Level of 2.1 children per woman.

Stage 5 (Natural Decrease) occurs in advanced HICs with extreme social and economic pressures, such as Japan, Germany, and Italy. Here, the birth rate falls below the death rate. Interestingly, the death rate shows a slight increase due to an ageing population (a higher proportion of elderly people). This results in negative growth, causing the total population to officially decline. The population pyramid for a Stage 5 country becomes "top-heavy", with a narrower base than the middle or top sections.

Limitations of the DTM

Does a theoretical model based on 18th-century Europe truly reflect the modern world? The DTM is incredibly useful, but it has several critical limitations that you must evaluate in an exam.

Firstly, the DTM does not account for migration. A Stage 4 or 5 country, like the UK, may still see its total population increase due to immigration, even if its natural change is zero or negative.

Secondly, the model is highly Eurocentric. It is based on the UK's historical transition from 1760. Modern LICs may transition through the stages much faster today because they can "import" advanced medical technology rather than waiting to invent it. Finally, the standard DTM ignores sudden, catastrophic events that cause sharp spikes in death rates, such as major conflicts or the HIV/AIDS epidemic.