Population change and structure
The demographic transition model
The demographic transition model [demographic transition model: A measure of population change over time which tracks birth and death rates. ] shows population change over time. It studies how birth rate and death rate affect the total population of a country.
The five stages of the demographic transition model
- Total population is low but it is balanced [balanced: A population is in balance when birth rates equal death rates. ] due to high birth rates and high death rates.
- Total population rises as death rates fall due to improvements in health care and sanitation. Birth rates remain high.
- Total population is still rising rapidly. The gap between birth and death rates narrows due to the availability of contraception and fewer children being needed to work - due to the mechanisation of farming. The natural increasenatural increase: The natural growth of a population due to the number of births exceeding deaths. is high.
- Total population is high, but it is balanced by a low birth rate and a low death rate. Birth control is widely available and there is a desire for smaller families.
- Total population is high but going into decline due to an ageing population. There is a continued desire for smaller families, with people opting to have children later in life.
As a country passes through the demographic transition model, the total population rises. Most LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] are at stage 2 or 3 (with a growing population and a high natural increase). Most MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ] are now at stage 4 of the model and some such as Germany have entered stage 5.
The demographic transition model
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 divergediverge: Move away from each other., as the death rate falls relative to the birth rate. In stage 3 they converge [converge: Move towards each other. ] 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.
Limitations of the model
- The model was developed after studying the experiences of countries in Western Europe and North America. Conditions might be different for LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] in different parts of the world.
- The original model doesn't take into account the fact that some countries now have a declining population and a 5th stage. Most texts will now show this stage as it is relevant to an increasing number of MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ] in the 21st century.