However, demographic transition has not followed the same course in all parts of the world (Figures 8.3-8.5). In the developed countries it took a very long time for mortality and fertility to decline and since the changes in both of them were slow, they did not experience a population explosion (i.e., a very high rate of growth of population). In less developed countries mortality remained high till the middle of the twentieth century and declined suddenly in the third quarter of the century. In the absence of a corresponding decline in fertility, which is taking much longer time, they experienced a very rapid growth rate of population, often exceeding three percent, implying a doubling time of 23 years. It is easy for any state to work effectively towards reducing death rates and improving health facilities that everyone welcomes, but it is difficult to change reproductive behaviour which requires sustained motivation on the part of individual couples.