The demographic transition model (DTM) is a model showing how birth rates and death rates typically change as a country develops economically and socially. These changes determine the rate of natural population increase. It is core content for SL and HL in IB ESS subtopic 8.1, Human populations.
The model treats a population as a system. Births are inputs and deaths are outputs; the difference between them produces natural increase or natural decrease. Migration is not directly represented by the standard DTM.
| Stage | Birth and death rates | Population change and explanation |
|---|---|---|
| 1 | High birth rate; high, fluctuating death rate | Little long-term growth. Disease, food shortages, and limited healthcare keep mortality high. |
| 2 | High birth rate; rapidly falling death rate | Rapid growth. Sanitation, food supply, and healthcare improve before fertility declines. |
| 3 | Falling birth rate; low death rate | Growth slows. Urbanization, education, contraception, and changing opportunities for women reduce fertility. |
| 4 | Low birth rate; low death rate | Population is large but stable or grows slowly. |
| 5 | Very low birth rate; low or rising death rate | Natural decrease and population ageing may occur, although this stage is not universal. |
For example, Niger displays characteristics associated with an earlier DTM stage, including high fertility and rapid population growth. Germany displays later-stage characteristics, including low fertility and an ageing population. Comparing two named countries in different DTM stages is HL-only syllabus content.
A common misconception is that every country follows the DTM in exactly the same way. It is a simplified model, so migration, government policy, conflict, epidemics, cultural values, and unequal development can produce exceptions. Policies affecting education, healthcare, reproductive rights, or migration also raise questions of perspective and social justice.
Exam technique: For “describe,” state the trends in both birth and death rates. For “explain,” connect each change to causes such as healthcare, urbanization, or female education. When evaluating the DTM, identify both its usefulness for comparing population change and its limitations as a generalized model.