Age of entry into marriage and the date of the initiation of voluntary birth control.

It is widely known that modern economic development has been accompanied by the initiation and spread of effective limitation of fertility, and that generally the populations which experienced development at a late date also had a belated reduction in childbearing. Here a surprising relation is found between (and within) broad regions: the areas in which traditional age of entry into marriage was late were the areas in which marital fertility was reduced first.