An Economic Model of Teen Motherhood: Opportunity Costs, Biological Constraints and the Timing of First Birth

and seminar participants at various universities for helpful comments and suggestions. 2 ABSTRACT This paper uses data from the National Longitudinal Survey of Youth to evaluate an economic model of the timing of first birth. We estimate a Tobit-type model, in which a woman chooses her age of first birth based on economic factors subject to the biological constraint that the birth must occur after physical maturity. This model fits the empirical distribution of first birth across a wide range of women. Biological constraints are important, with late maturity associated with low birth rates by age 17 and high birth rates in the later teen years. School achievement, as measured by the Armed Forces Qualification Test (AFQT), accounts for all of the racial differences in timing of first birth and predicts a 10-fold difference in teen-motherhood between top and bottom deciles of achievement. Finally, we find that the model is consistent with self-reports about expected age of first birth and whether a pregnancy was wanted.