Observations on the History of Cohort Fertility in the United States

Abstract

This article has exploited a valuable set of data: completed parity distributions for the cohorts of 1867 through 1955 for women in the US. The history is a familiar one: long-term decline with a transitory reversal about a generation ago. In considering the time series of aggregate fertility a measure of mean sibship size was introduced in order to represent fertility from the standpoint of the children rather than as is conventional from the standpoint of the parents. Understanding of the determinants of the time series of cohort total fertility is enhanced by a consideration of the time series of progression ratios for successive parities. Progression ratios beyond parity 2 show characteristics quite unlike those for the lower parities. In order to come to closer grips with theoretical issues a model of the components of parity progression has been developed. The model is 1st used to contrast the values of the fundamental demographic parameter the intrinsic rate of natural increase for all births and then for intended births. The conclusion reached is that population growth in the US over the past 8 decades has had 3 components: immigration mortality decline and unintended births. The pattern of change in the intended parity distribution shows a systematic monotonic rise in the proportion intending 2 births from 13% for the earliest cohort to 43% for the latest cohort. This transformation has been accompanied by an equally systematic decline in the mean number of intended additional births for those with at least 3 births from 3.2 at the beginning of the series to 0.5 at the end of the series. The final application of the model is to test the proposition that progression is insensitive to parity beyond parity 2. While this is true for observed progression it is not true for intended progression.