8.2 Measurement of fertility

We talk about fertility when comparing the number of liveborn children with women of fertility age (usually aged 15 to 49).

Age group-specific fertility rates are generally calculated either by five-year age group or one-year age group by comparing the numbers of children born to women of a certain age with the mean female population of the same age. To make the comparison easier the figure derived is multiplied by one thousand.

Age group-specific fertility rates express women's probability to give birth at a certain age when the figure is not multiplied by one thousand. When these probabilities are added up, the sum indicates the average number of children born to women. This is called the total fertility rate.

The total fertility rate is perhaps the best describer of fertility and it is usually used when comparing the fertility of different countries. The total fertility is the sum of age group-specific fertility rates. The total fertility rate is most typically calculated using women's data by five-year age group. The figure obtained is multiplied by five because each age group has five one-year age groups.

The general fertility rate is derived by comparing the number of children born yearly with the number of women aged 15 to 49. This figure is multiplied by one thousand. The general fertility rate has not been used much in the last few years as it has been replaced by the superior total fertility rate.

Examples