The crude birth rate, as has been pointed out earlier, is not a useful measure for analytical purposes for it is affected by the age and sex distribution of the population.
A rate, therefore, which would eliminate the effects of the demographic composition, is required when the fertility of two populations is to be compared.
The total fertility rate and the gross reproduction rate are useful for such purposes. The effects of the age-sex structure of the population on the crude birth rate can be reduced to the minimum by computing the sex-age adjusted birth rate.
The United Nations has defined the sex-age adjusted birth rate “as the number of births per 1,000 of a weighted aggregate of numbers of women in the various five-year age groups from 15 to 44.
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The United Nations has recommended a standard set of weights in computing this aggregate. These are 1, 7, 7, 6, 4, 1, which correspond to the average pattern of age specific fertility rates for the five-year age groups, 15-19, 20-24, 25-29, 30-34, 35- 39 and 40-44 respectively.
The weights are “roughly proportional to the typical relative fertility rates of various age groups” and have been derived from a study of the data from 52 countries, of which 15 had comparatively high fertility and 37 had low fertility.