4.6 Demographic Transition and Age Structure

Notes

The demographic transition model describes how birth and death rates change as a country develops.

• Stage 1: high birth and high death rates; population stable and small.
• Stage 2: death rates fall (better food, medicine) while birth rates stay high; rapid growth.
• Stage 3: birth rates fall; growth slows.
• Stage 4: low birth and low death rates; population stable or slowly growing.
• Some countries are in a later stage with birth rates below death rates, so the population shrinks.
• Age structure diagrams: a wide base (many children) means rapid growth; a narrow base with a large older population means slow or negative growth. Population momentum means a young population keeps growing for decades even after fertility falls.
• Example: a country with high birth rates and falling death rates is in stage 2.