The demographic transition model (DT) is the transition from high birth

Birth rate

Crude birth rate is the nativity or childbirths per 1,000 people per year . Another word used interchangeably with "birth rate" is "natality". When the crude birth rate is subtracted from the crude death rate, it reveals the rate of natural increase...

 and death rates to low birth and death rates as a country develops from a pre-industrial to an industrialized economic system

Economic system

An economic system is the combination of the various agencies, entities that provide the economic structure that defines the social community. These agencies are joined by lines of trade and exchange along which goods, money etc. are continuously flowing. An example of such a system for a closed...

. The theory is based on an interpretation of demographic

Demography

Demography is the statistical study of human population. It can be a very general science that can be applied to any kind of dynamic human population, that is, one that changes over time or space...

 history developed in 1929 by the American demographer Warren Thompson (1887–1973). Thompson observed changes, or transitions, in birth and death rates in industrialized societies over the previous 200 years.
Most developed countries are in stage 3 or 4 of the model; the majority of developing countries have reached stage 2 or stage 3.