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RELATIVE INFLUENCES ON RECENT CHANGES IN THE FIRST BIRTH RATIO IN THE UNITED STATES
ROSALIND BERKOWITZ KING a1 a1 Demographic and Behavioral Sciences Branch, Center for Population Research, National Institute of Child Health and Human Development, National Institutes of Health, US Department of Health and Human Services, USA
Researchers in psychology have focused a great deal of attention on the potential greater predisposition to achievement among first-born children relative to their siblings. Focusing on the United States as an example, a time series of the first birth ratio is used to show how the changing prevalence of first births relative to higher order births has altered the composition of birth cohorts, and the ratio is decomposed into four factors. Results show that the ratio increased significantly in the 1960s and early 1970s, but changed only slightly in the following decades. While more recent birth cohorts are composed of larger proportions of first-born children, the majority of children are still born as siblings. Contrary to expectations, the primary source of change was the proportion childless rather than decreasing higher order birth rates.