Modelling Diffusion Effects in Fertility Transition

Abstract In this article we use a simple mathematical model to study the implications for fertility transition of the diffusion of birth-control practices through social interaction. The model proposed is dynamic and deterministic. The simulations demonstrate that interaction diffusion can make potentially large contributions to fertility declines. These contributions tend to be larger under more restrictive demand and supply conditions and, not surprisingly, in populations characterized by higher levels of social interaction about reproduction. Moreover, if social interaction is intense enough, fertility differentials fade away and fertility change resembles an imitation process. A direct implication of the model, clearly illustrated by the simulations, is that reduction in birth-control costs can stimulate greater demand for birth control. The simulations also illustrate the effects of geographical and social distances on fertility differentials, the pace of fertility transition, and the timing of the onset of transition. The strength of social-interaction diffusion is heavily conditioned by two sets of factors, which thus assume great significance as determinants of the course of fertility transition: the development of communication and transport networks, and the patterns of customary social interaction permitted by the social structure.