Another summary measure for measuring current fertility is the Gross Reproduction Rate. While the total fertility rate refers to the total number of children cohort of women is expected to have, the gross reproduction rate is restricted only to the number of female children.

If data on births by sex are available for each age group in the reproductive age group, the age specific fertility rates may be computed for female children.

While the gross reproduction rate may be computed by summing up such age specific fertility rates, multiplying the sum by 5, and finally dividing the product by 1,000.

The data on births by sex, however, is usually not available. In such cases, the gross reproduction rate is computed simply by multiplying the total fertility rate by the factor 0.49.

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This factor is arrived at by assuming that the sex ratio at birth is 105 male babies per 100 female babies.

Thus the proportion of females in the total number of births is 100 h- 205 which is approximately 0.49. The gross reproduction rate for the sample area in Calcutta city is therefore 2.34 x 0.49 = 1.15.

From this, it is obvious that the gross reproduction rate is essentially a total fertility rate, with the (modification that it is computed only for female births.

It may also be observed that the value of the gross reproduction rate is about one half of that of the total fertility rate. As in the case of the total fertility rate, the gross reproduction rate, too, assumes that women in the reproductive age groups would survive till the end of their child-bearing period.

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In brief, the gross reproduction rate indicates the number of daughters each woman can bear by the time she passes out of the reproductive period, if she continues to have children, according to a particular schedule of age specific fertility rate, throughout her reproductive period. This rate is generally used while comparing the current fertility of various groups.

The gross reproduction rate is an important measure in the study of replacement, which is concerned with the extent to which a group replaces its own number by the natural processes of fertility and mortality.

The gross reproduction rate indicates the number of daughters a cohort of women is expected to produce, if there is no attrition in the cohort due to mortality.

As it is not realistic to assume that all the women in the cohort will survive up to the end of the child-bearing period, a refinement in the gross reproduction rate is introduced by taking into account the mortality of the women, and the net reproduction rate is computed.

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(Thus the gross reproduction rate is an intermediate step in computing the net reproduction rate). The net reproduction rate indicates the number of daughters ever born to a cohort of women, if they give birth according to the fixed schedule of age specific fertility rates and experience fixed age specific mortality rates up to the end of their child-bearing period.

The net reproduction rate thus measures the extent to which a cohort of newly born girls will replace their mothers under pre-determined schedules of fertility and mortality.