[2] A major purpose of demography is to inform government and business planning of the resources that will be required as a result of population changes.
Infant mortality was high for various reasons such as ignorance, insufficient health facilities, and sometimes lack of food.
Occasionally, farmers were unable to produce enough food for the population, resulting in death from starvation.
However more recently, and especially in the 20th and 21st centuries, due to growth in technology, education, and medical care, the world population has increased rapidly, as many more people have survived to child-bearing age.
[4] In many countries, fertility rates have declined, due to better education, better available birth control, better pension provision reducing economic dependence on one's children in old age, and in response to lower infant mortality.