While computing the crude birth rate, the denominator includes the total mid-year population.
It is obvious that everyone in the total population is not exposed to the risk of pregnancy and that all males as well as females below the age of 15 and above the age of 44 or 49 need to be excluded from the denominator, for they cannot produce children.
Hence, the first refinement of the crude birth rate is introduced by relating the number of births to the number of women in the child- bearing age (15 to 44 or 49).
The rate thus computed is known as the General Fertility Rate and may be defined as the ratio of total live births in some specified year in a particular area to the number of women in the child-bearing age, multiplied by 1,000. It is computed as follows:
The general fertility rate of 86.61 indicates that, in 1967-68, in the sample area of Calcutta city, there were 86.61 births per 1,000 women in the child-bearing age group.
Though the general fertility may be considered as a forward step in the direction of the refinement of fertility measures, it must be noted that it is not a very effective refinement, for it is related to all the women in the child-bearing age group.
But it is well known that fecundity that is, the physiological capacity to bear children during the child-bearing years is not uniformity distributed. The hypothetical fecundity curve as well as the average age specific fertility rates for 72 countries.
It may be observed that the rate of child-bearing is low in the younger age groups (15-19), reaches its peak at ages between 20 and 29 when the majority are married and fecundity is as its maximum and then it tapers off, slowly in some countries and rapidly in others, till at the age of 50 it reaches at the zero mark.
The fact that the fecundity of women is not the same during the entire span of the child-bearing period tends to be lost sight of, when the general fertility rate is computed.
For this reason, this rate is not considered to be a very effective refinement. Further refinement in the measurement of fertility is incorporated when age specific fertility rates are computed.