It studies how birth rate and death rate affect the total population of a country. It shows marked differences between LEDCs and MEDCs.
As a country passes through the demographic transition model, the total population rises.
Most LEDCs are at stage 2 or 3 (with a growing population and a high natural increase).
Most MEDCs are now at stage 4 of the model and some such as Germany have entered stage 5.
As populations move through the stages of the model, the gap between birth rate and death rate first widens, then narrows.
In stage 1 the two rates are balanced. In stage 2 they diverge, as the death rate falls relative to the birth rate.
In stage 3 they converge again, as the birth rate falls relative to the death rate.
Finally in stage 4 the death and birth rates are balanced again but at a much lower level.
Stage 1: Total population is low but it is balanced due to high birth rates (36/37 per 1,000) and high death rates (36/37 per 1,000). Countries at this stage will usually be undeveloped.
Stage 2: Total population will start to rise because the death rates will start to fall (to around 18/19 per 1,000). Birth rates will remain high. Death rates fall due to:
Stage 3: Total population is rising rapidly. The gap between birth and death rates will narrow. Natural increase is high. Death rates will now remain low and steady (to 15 per 1,000) but birth rates will fall quickly (down to around 18 per 1,000). Birth rates fall due to:
Stage 4: Total population is high and growing slowly. It is balanced by a low birth rate (15 per 1,000) and a low death rate (12 per 1,000). Contraception is widely available and there is a social desire to have smaller families.
Stage 5: Total population is still high but starting to decline due to the birth rate falling (to 7 per 1,000) below the death rate (9 per 1,000). The population will start to fall as it is no longer replacing itself. The population is ageing and will gradually be dominated by older people.