The total fertility rate is the sum of the age specific fertility rates of women in each five-year age group from 15 to 44 or 49.
The procedure for computing the total fertility rate is illustrated in Table 8.1 and may be explained as follows: Age specific fertility rates for the sample area in Calcutta city during 1967-68 are given in column 4 of Table 8.1.
The sum of these age specific fertility rates (467.15), given at the bottom of the Table, is multiplied by 5 because each age group consists of women of 5 different ages (for example, the age group 15-19 consists of women of 15, 16, 17, 18 and 19 years).
As the total fertility rate is generally expressed per woman, the product (after multiplying the sum of the age specific fertility rates by 5) is divided by 1,000. Thus in Table 8.1, the total fertility rate observed for women in the sample area of Calcutta city during 1967-68 was 2.34.
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The total fertility rate is a hypothetical rate indicating “the total number of children that would ever be born to a (hypothetical) group of women, if the group passed through its reproductive span of life with these birth rates in each year of age.”
The total fertility rate assumes that the women in this hypothetical cohort or group would survive till they reach the end of the reproductive period.
As the total fertility rate is not affected by the age structure of the women under study, it is an effective summary rate for describing the frequency of child-bearing in a year.
It is also useful when comparisons between the reproductive performances of two groups of women are made, for it is standardised for age and is just one summary measure.