Marriage, Depression, and Mortality Across the Life-Span

This dissertation addresses the causal influence of marital formation and marital dissolution on depression and risk of early mortality, including suicide. Although many studies have shown that marriage is correlated with fewer physical and mental health problems, the causal role of marriage in producing these favorable outcomes is uncertain. Spouses provide support, which may be one reason why marriage has been found to be beneficial. However, healthier people may select into marriage more frequently than unhealthy people, minimizing the causal role of marriage. The general research questions addressed include: (1) Does marrying decrease the severity of adults’ depression over the lifespan? (2) Does becoming widowed increase the severity of adults’ depression in late adulthood? (3) Does divorce increase the risk of early mortality, especially by committing suicide? The overall hypothesis tested in this dissertation is the following: Marriage is a protective factor against depression and mortality across the marital lifespan.

This dissertation extends prior work on the benefits of marriage by using several longitudinal twin samples to parse genetic and environmental selection from the potential causal influences of marriage. By adjusting for genetic and environmental selection factors that make twins similar to one another, twin designs provide the closest approximation to random assignment to within-family environmental “conditions” in nonexperimental research.

Three longitudinal twin studies were conducted to test the protective role of marriage over the lifespan. The first study addressed whether entering marriage predicts lower severity in subsequent measures of depression over the lifespan, using data from the National Longitudinal Study of Adolescent Health (Add Health) twin sample and data from the Swedish Adoption/Twin Study on Aging (SATSA) sample. The second study addressed whether becoming widowed predicts increases in subsequent depression during the second half of the lifespan, using five waves of data from the SATSA sample. Additionally, twins who were discordant for becoming widowed were used to test whether depression mediated the association between widowhood and risk of early mortality. The third study addressed whether divorce raises the risk of early mortality, particularly by suicide, using twins’ birth records, death records, and marital histories from two cohorts in the Swedish Twin Registry (STR).