Unmarried births: Accounting and equilibrium analysis, 1960-1995

The share of births to unmarried women in the U.S. rose well above 30% in the 1990s, despite unmarried women having greater access to abortion and improved birth control. We show that an equilibrium matching model in which unmarried couples behave co-operatively can explain 97% of the rise in the UMB ratio as the response to a combination of well-documented shocks: rising divorce rates, access to abortion, and improved contraception. Equilibrium interactions among these factors are important; had the marital surplus remained constant, very little change in unmarried births would have occurred. We also find that reforms reversing accessibility of birth control or abortion would on their own do little to reverse these social trends.