Insights from a Sequential Hazard Model of Entry into Sexual Activity and Premarital First Births

Lawrence L. Wu, New York University
Steven P. Martin, New York University

This paper discusses a model that supposes that women become at risk of a premarital first birth only after becoming sexually active. We use the resulting sequential hazard framework to further decompose the probability of a premarital first birth into components reflecting: (1) differences in exposure to risk via earlier or later sexual onset and (2) differences in risks following onset. Our empirical analyses, using data from the 1979 National Longitudinal Survey of Youth, replicate previous findings that socioeconomic disadvantage is associated with earlier sexual onset and higher premarital first birth risks. However, results from our decompositions show that group differences in onset timing have far a smaller influence on premarital first birth probabilities than do group differences in risks following onset. We conclude by speculating on the possible substantive and policy implications of these results, particularly with respect to ongoing debates between proponents and critics of abstinence education.