Period and Cohort Effects in Nonmarital Childbearing in the United States, 1970-2009

Paula Fomby, University of Colorado at Denver
Stella Min, University of Colorado at Denver

We test two hypotheses to explain the rise in nonmarital childbearing in the United States since the 1970s. The cohort hypothesis posits that the historical rise in nonmarital childbearing resulted from changing norms about premarital sex, cohabitation, and single parenthood that successive cohorts of young adults have introduced and reinforced over time. The period hypothesis asserts that social change works not just through cohorts of young adults, but also through historical circumstances that affect all birth cohorts simultaneously. In the case of nonmarital childbearing, supporters of the period hypothesis point to structural changes during the last forty years that have reduced women’s and men’s incentives to marry regardless of their cohort membership. We use the age-period-cohort (APC) intrinsic estimator method to test our research hypotheses. Data come from six repeated cross-sections of the National Survey of Family Growth (NSFG), designed and administered by the National Center for Health Statistics.