THE CONSEQUENCES OF TEENAGE CHILDBEARING: CONSISTENT ESTIMATES WHEN ABORTION MAKES MISCARRIAGE NON-RANDOM

Miscarriage, even if biologically random, is not socially random. Willingness to abort reduces miscarriage risk. Because abortions are favourably selected among pregnant teens, those miscarrying are less favourably selected than those giving birth or aborting but more favourably selected than those giving birth. Therefore, using miscarriage as an instrument is biased towards a benign view of teen motherhood, whereas ordinary least squares (OLS) on just those giving birth or miscarrying has the opposite bias. We derive a consistent estimator that reduces to a weighted average of OLS and IV when outcomes are independent of abortion timing. Estimated effects are generally adverse but modest.