Phase I is mostly seen in pre-industrialized countries (Galloway & Patrick,1986).
Most developing countries are in the Phase II of the transition. In the second phase, the state of equilibrium in the population is lost and death rate is exceeded by birth rate thereby leading to a “population explosion.” This change is subjected to the fact that better facilities such as good sanitation, nutrition, health facilities etc. are implemented. Such measures help in checking the rate of mortality and increase the lifespan. Though the death rate is lowered the birth rate remains high because most of the people looks upon children as assets who will help bring in money into the family. These growths in population triggers the next stage of transition i.e. Phase III. In this phase a decline in birth rate is seen. This decline is seen because the population is educated and use contraception. Most of the people earn more and therefore do not look upo children as assets and parents realize that children need to be looked after well (Lee, 2003,p 170).“Some of the improvement in child survival is itself a response to parental decisions to invest more in the health and welfare of a smaller number of children” (Nerlove, 1974). In phase IV, both birth and death rates reduce drastically. This is because of societal changes where too many children are looked upon as hindrance in leading a good satisfactory life and hence both fertility and birth rate falls.
According to researchers, the factors that are primarily responsible for declination in the Crude Birth rate include education among women, use of contraceptives, medical facilities which help in survival of babies thereby eliminating need for reproduction of more babies. On the other hand better health facilities, newer technologies and infrastructure, faster transport and higher earnings trigger declination in Crude Death rate.