A Model for Cohort Fertility Schedules in Low and Moderate Fertility Populations
Joshua R. Goldstein, Max Planck Institute for Demographic Research
I re-introduce the Gompertz model of age-specific fertility. This model was rejected by past authors as sometimes fitting poorly _period_ rates. However, I find the model fits very well to recent medium and low fertility _cohort_ schedules in France, Denmark, and Japan. A distinct advantage of the Gompertz model its simple behavioral interpretation as the social diffusion of fertility behavior in a cohort competing with the fertility-depressing effects of older age. The Gompertz model, and further refinements, offer a means for forecasting future fertility and assessing the fertility-limiting effects of older entry into motherhood. I estimate the completed cohort fertility of French and Japanese cohorts born in 1965 as 2.0 and 1.6, respectively. For France, this represents only minor decline from earlier cohorts, but for Japan the decline is marked.