This dissertation investigates various health behaviors, weight, binge drinking, and breastfeeding related to social interactions and trends in various group settings.

The first chapter examines the effect of peers on weight through the tolerance effect and eating behavior effect by measuring the effect of relative weight, while controlling for absolute weight. A cross sectional study of high school students reveals that students surrounded by heavier peers will see themselves as thinner and want to lose weight less often at any given weight. Peer is defined as individuals in the same grade and of the same gender as the student. This peer effect in high school students represents a self fulfilling prophecy of the upward trend in obesity in adolescents.

The second chapter examines the causality of fraternity and sorority membership on binge drinking in college students which is an important health concern. We employ a nonparametric approach which is believed to be a better fit to model binge drinking due to the parametric model being misspecified. The results suggest, contrary to previous research, that fraternity and sorority membership does not have a causal relationship with binge drinking. Binge drinking is more closely related to other types of risky behavior, including risky sexual behavior. Policies to reduce binge drinking should be aimed at these students rather than all students associated with Greek membership.

The third chapter investigates the relationship between breastfeeding, weight, and returning to work. I examine the role of types of work on breastfeeding initiation and duration while also controlling for mother fixed effects. Many medical associations promote breastfeeding; however, many women are also part of the labor force. Results suggest that returning to work in six weeks and three months has a negative effect on breastfeeding initiation, and returning to work at three, six, and twelve months has a negative effect on duration. As well, job category has a significant effect on breastfeeding initiation and duration. Being overweight also has negative effects on breastfeeding, but is not consistent across fixed effects models.