ESSAYS IN DEMOGRAPHIC ECONOMICS

In the ¯rst of the essays, I reassess the relationship between premarital cohab-itation and marital instability both theoretically and empirically. It has become astylized fact that premarital cohabitation is positively correlated with the likelihood ofmarital dissolution. This is counterintuitive because economists expect that coupleslearn about each other during cohabitation and would only get married if they antic-ipated a successful marriage. One prominent explanation for the antithetic empiricalevidence is self-selection of individuals with lower prospects of successful marriagesinto premarital cohabitation. Using U.S. data from 1988 to 2002 and duration mod-els, I demonstrate that the positive relationship between premarital cohabitation andmarital instability has weakened over time, and that the two are no longer associatedwith each other. A strong decline in this association within the group of more edu-cated women drives the result. I hypothesize that a decline in the bene¯ts of marriagehas led to greater cohabitation and hence less self-selection within this group. Causalmodeling using matching and panel models uncovers a negative e®ect of cohabitationon marital instability.In the second essay, I investigate the e®ect of teenage childbearing on high schoolcompletion, and why alternative sets of instruments result in di®ering coe±cientestimates. The three main reasons for these discrepancies are defective instruments,treatment e®ect heterogeneity, and multiple mechanisms by which instruments a®ectthe treatment. I use two instruments, age at menarche and the occurrence of amiscarriage, to investigate which of these is likely to hold. While I do not ¯ndsigni¯cant treatment e®ect heterogeneity, I ¯nd some indications that there may beproblems with the instruments' validity. Furthermore, miscarriage disproportionatelya®ects very young teenagers which are in turn more likely to drop out of high school.This may explain di®erences in instrumental variable estimates if age at birth is anadditional explanatory variable.