The effect of abortion legalization on sexual behavior: evidence from sexually transmitted diseases.

Unwanted pregnancy represents a major cost of sexual activity. When abortion was legalized in a number of states in 1969 and 1970 (and nationally in 1973), this cost was reduced. We predict that abortion legalization generated incentives leading to an increase in sexual activity, accompanied by an increase in sexually transmitted diseases (STDs). Using Centers for Disease Control data on the incidence of gonorrhea and syphilis by state, we test the hypothesis that abortion legalization led to an increase in sexually transmitted diseases. We find that gonorrhea and syphilis incidences are significantly and positively correlated with abortion legalization. Further, we find a divergence in STD rates among early legalizing states and late legalizing states starting in 1970 and a subsequent convergence after the Roe v. Wade decision, indicating that the relation between STDs and abortion is casual. Abortion legalization accounts for about one-fourth of the average disease incidence.