Fecundability and the Frequency of Marital Intercourse: A Critique of Nine Models

The biological and demographic literature on the effects or frequency of intercourse on fecundability is reviewed in this paper. While empirical work and model-building results agree well on the effect of change from low to moderate coital frequencies, inconsistencies emerge when increase from moderate to high coital frequencies is considered. Of the models considered, it may be argued that the explicit provision for unfavourable cycles makes Schwartz's model an improvement over Barrett and Marshall's, Lachenbruch's and Trussell's. Moreover, even though he used a very different approach, Bongaarts obtained results that are much closer to those of Schwartz et al. than the others. Bongaarts's model is used as a starting point for new modelling, to be reported in the next issue, which deals with these inconsistencies by taking into account the ageing of gametes.