Fertility, Measures of

Birthrate

Birthrates, also known as crude birthrates, represent the actual number of live births per 1,000 population per year. It is mathematically represented by the following equation:

where n represents the number of live births in that year and p is the population size in that year.

Similarly, the general fertility rate is the number of live births per 1,000 women of reproductive age (usually ages 15 to 44 or 15 to 49) in a given year.

Age-Specific Fertility Rate

The ASFR is a measure of the average number of births per year per 1,000 women in specific age groups (generally ages 15 to 19, 20 to 24, etc.). The following equation represents the calculation of ASFR:

where ni represents the number of live births during a given year by women in age group i, and wi represents the number of women in age group i:

Total Fertility Rate

The TFR measures the average number of children who would be born alive to a woman completing her childbearing years based on ASFRs in a given year. Thus, TFR is not an actual rate of live births but an estimate based on the assumption that women will continue childbearing at the ASFR in that year. Mathematically, TFR is calculated from ASFR:

where ASFRi represents the fertility rate for the ith age group and x is the number of years in the interval of age group i:

TFR is often referred to in the context of replacement-level fertility, the TFR necessary to sustain current population size. In industrialized nations, a TFR of 2.1 indicates a level of fertility where each couple bears only enough children to replace themselves in a population, representing equilibrium between birth and death rates. Replacement-level fertility in developing countries is less defined, particularly due to varying death rates in the context of HIV/AIDS.

Other Measures

Other measures of fertility include the following:

• Completed Fertility Rate. The actual number of children born to a cohort of women at the end of their childbearing years.
• Gross Reproduction Rate. The average number of live female births that would be born during a woman's lifetime if she passed through her reproductive years conforming to ASRF in a year.
• Marital Fertility Rate. The actual number of live births to married women per 1,000 women of reproductive age in a year.