ABSTRACT
This chapter reviews some methods that have been developed in recent years for isolating the sources of variation in natural fertility. In trying to account for variation in fertility, one might be tempted to catalog every single factor potentially affecting reproduction, including socioeconomic variables such as religious affiliation or wife's educational background, behavioral variables such as coital frequency, and a host of physiological variables ranging from maternal nutritional status to the frequency of ovulation or the viability of sperm. Such a catalog, even if possible to compile, would tell us little about which of these variables are likely to be most important in explaining fertility variation. Fecundability is determined by several behavioral and physiological factors, only two of which are explicitly recognized by Bongaarts. In assessing the fertility-reducing effects of breastfeeding, account must be taken not only of the prevalence of breastfeeding but also of the average amount of time that it adds to the birth interval.
