A microsimulation model of human fertility : theory and applications to the Yoruba of Western Nigeria

Abstract

The thesis falls naturally into two parts, with the first being concerned with the construction and validation of a model and the second with the use of the model as an experimental tool. In the first part, comprising Chapters One to Four, an examination of historical and contemporary models of population growth led to the decision to study changes in fertility by means of a biological microsimulation model. This model was tested against Hutterite data after the reasons for using such a model had been discussed, and after the "best" input data had been selected and variations in these data tested on the model. The main emphasis of the second part of the thesis, comprising Chapters Five to Eight, was the testing of the effect on Yoruba fertility of variations in the duration of the post partum period of non-susceptibility to conception and in the level of infant and child mortality rates; further simulations were performed to discover the impact on fertility of the use of contraception to attain different family sizes both with and without the additional effect of infant and child mortality. The model was also used to test the efficiency of the Brass method of estimating childhood survivorship rates under different levels of fertility and mortality. Low fertility simulations were performed to assess the effect of different spacing strategies on ultimate family size. The simulations quantified our notions of the extent to which the Westernisation of the Yoruba is capable of producing an increase in average parity, one facet of this Westernisation being the widespread abandonment of long periods of post partum sexual abstinence without the compensatory adoption of efficient contraception. Declines in the infant mortality rate were also seen as an aspect of "modernisation" which has contributed to increased fertility, and suggestions were made for further simulations to test the magnitude of the increases which could be expected to occur through decreased levels of adult morbidity and mortality. As one would neither want morbidity and mortality rates to revert to former levels, nor be able to reinstate the post partum taboo to its previous level of importance, suggestions are presented for the institution of effective family planning programmes. Bearing in mind, also, the results of the low fertility simulations of the penultimate chapter, some indication is given of the desirable progression of the rationale for the use of contraception.