Relationship between birth rate and infant mortality under natural reproduction situations

The author investigates the relationship between infant mortality and the birth rate. "For this research, a number of countries with representative features are selected from different parts of the world. The study focuses on mortality and birth in these countries in the 25 year span between 1945 and 1970. A major reason for selecting these countries is that they are in a natural reproduction situation...[which] refers to a reproductive condition without any government intervention."