The present study examines developmental differences in the interactive effects of DRD4 polymorphism and friends' drinking on alcohol use across four developmental phases: late adolescence (ages 16-18), emerging adulthood (ages 20-25), early young adulthood (ages 26-30), and later young adulthood (ages 30-35). Because the relationship between peer and own alcohol use is dynamic and involves both selection of friends with similar drinking habits and peer influence (Burk et al., 2012), we model both types of mechanisms (peer selection and socialization) across the developmental periods examined. We also include two related, yet distinct alcohol use outcomes -- levels of alcohol use (standard quantity-frequency index) and heavy episodic (or binge) drinking. By examining two alcohol phenotypes across four developmental periods, we are able to determine the developmental and phenotype-related specificity of the DRD4 by peer drinking interactions.
