Fertility Rate

The study of fertility is crucial to understanding the dynamics of population change. The term fertility rate refers to the actual reproduction in any given society, i.e., the number of children that are born to an individual or in a population in a given time period. This is in contrast to the term fecundity, which refers to the biological or physiological ability of individuals or couples to have children; some people in a society are unable to bear children because of disease or other biological, genetic, and environmental factors. The theoretical maximum fecundity for any given population is said to be 15 children per woman, but the actual number of children per woman rarely exceeds eight. There are several factors that explain the large gap between fecundity and the actual reproduction (fertility) and interfere with the process of human reproduction. The determinants of fertility include the value placed on children, cultural and social roles of women, and socioeconomic circumstances. For example, in less-developed societies, large families are often the norm as children contribute significantly to livelihoods and often take care of their parents in old age. More importantly, infant mortality rates are higher in these societies, as parents know that some of their babies will succumb to death. On the other hand, in highly developed societies, economic realities may deter parents from having large families.

The cultural, social, and economic determinants of fertility work indirectly to affect another set of factors, which demographer John Bongaarts termed the four proximate determinants of fertility. The four proximate determinants are the proportion married, the percent of women using contraception, the proportion of women who are infecund due to disease or prolonged breastfeeding, and the level of abortion. In highly developed regions, fertility rates are extremely low because of relatively high rates of contraception use and a low rate of marriage among women in their prime childbearing years. In the less-developed parts of the world, high fertility rates can be explained by low contraceptive usage and the promotion of early and universal marriage for women.

In developed regions, fertility rates are low because of a low rate of marriage among women in prime childbearing years.

Demographers use different types of formulae to measure the level of fertility in a given society for a given time period. Measures such as the crude birth rate, the total fertility rate, the general fertility rate, the child-woman ratio, age-specific birth rates, the gross reproduction rate, the net reproductive rate, and others have been devised to gauge the level of fertility in different societies. However, the two most commonly used and reported measures of fertility are the crude birth rate (CBR) and the total fertility rate (TFR). The CBR is expressed as the number of births per 1,000 population—a crude measure of fertility, as the denominator does not distinguish the age or sex structure of the population. In a young population there will obviously be more births than in a predominantly older population. Thus, the TFR is a more refined measure of fertility that takes [Page 662]into consideration the age and sex composition of a population. The TFR summarizes the average number of children a woman would have if she were to have children at the prevailing age-specific rates as she passed through her reproductive years.

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