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Stud Fam Plann. 1982 Jun-Jul;13(6-7):179-89.

The fertility-inhibiting effects of the intermediate fertility variables.


Based on the application of an aggregate reproductive model, this study demonstrates that a small number of intermediate fertility variables are responsible for most of the variation in fertility levels of populations. Four variables--proportion married, contraception, induced abortion, and postpartum infecundability--are generally the most important determinants of fertility; the other intermediate factors are of less interest except in unusual circumstances. These four factors explain 96 percent of the variance in the total fertility rate in a sample of 41 populations that include developing and developed countries as well as historical populations. In the last section, the average fertility effect of the principal intermediate fertility variables is estimated for groups of contemporary populations with different total fertility rates.


This paper demonstrates that differences in the fertility levels of populations are largely determined by variations in only 4 intermediate variables: proportion married, contraception, induced abortion, and postpartum infecundability. To determine the predictrive value of these 4 variables, the observed total fertility rates of 41 populations that included developed and developing countries as well as historical populations were compared with the model estimates of total fertility rates. Good agreement was found between these 2 fertility levels. The 4 intermediate fertility variables explained 96% of the variation in the observed fertility rate, confirming the general validity of the model. In addition, estimates of the fertility effects of these factors and of the levels of general fertility, marital fertility, and natural fertility were made for contemporary populations at various stages in the fertility transition. The data indicate that the transition from natural to controlled fertility is accompanied by a shortening of postpartum infecundability, a large increase in contraceptive use, and a decline in the proportion married.

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