The Net Reproduction Rate measures the extent to which mothers produce female infants who survive to replace them. It measures the extent to which a generation of girl babies survive and in turn give birth as they pass through the child-bearing age group.
The Net Reproduction Rate is defined as the average number of females born to a woman taking into consideration the mortality of the mothers. We need to include mortality because it might happen that a woman dies before her child-bearing age is completed.
If the net reproduction rate is 1 it means that a group of new born girls will exactly replace itself in the new generation. Thus in this case the population has a tendency to more or less remain constant. If the rate is greater than 1 then the population has a tendency to increase and if the rate is less than 1 the population has a tendency to decrease.
The Net Reproduction Rate usually ranges from 0 to 5 per annum.
Formula:
Suppose that the child-bearing age of a woman lies between the ages x and x+n. The probability of survival of a female between the age interval x and x+n is called the survival rate. If we know the survival rate then the net reproduction rate can be calculated using the formula,
\text{Net Reproduction Rate }= \sum_{i=x}^{x+n}[n \times \text{ Female Age Specific Mortality at Age }i\times \text{ Survival Rate}]Here the sum over i is taken over all ages in the reproductive span.
