Measurement of Fertility

At the outset, it is necessary to differentiate between fecundity and fertility. Fecundity refers to the physiological capacity to reproduce. Fertility, on the other hand, refers to the actual reproductive performance of an individual or a group. While there is no direct measurement of fecundity, fertility can be studied from the birth statistics. The crude birth rate is an important measure of fertility for which only live births, that is, children born alive are taken into account. The crude birth rate is calculated by dividing the number of live births occurring during a calendar year in specified areas by the midyear population of that year. The crude birth rate is generally expressed per thousand of population.

The crude birth rate directly points to the contribution of fertility to the growth rate of the population. It suffers from certain limitations mainly because it has in the denominator the total population which includes males as well as very young and very old women who are biologically not capable of having babies.

There are other more refined fertility measures like the general fertility rate, the age-specific fertility rates, etc., that overcome these limitations.

General Fertility Rate: It is the number of live births per 1000 women, aged 15-49 years (child bearing age group), in a given period.

Age-Specific Fertility Rate: The number of live births occurring during a given year or reference period per 1000 women of reproductive age classified in that age group.

ASFR = (Ba/Ea)* 1000, where

Ba – number of births to women in age-group in a given year or reference period.

Ea – number of person-years of exposure in that age-group during the specified reference period.

Total Fertility Rate: The total fertility rate refers to the total number of live births that a woman would have if she lived through the reproductive age group and had the average number of babies in each segment of this age group as determined by the age-specific fertility rates for that area.