Similarities in adolescent siblings' substance use: Testing competing pathways of influence

Objective: An accumulating body of work indicates that siblings uniquely influence each other's alcohol and substance use behaviors during adolescence. The mechanisms underlying these associations, however, are unknown because most studies have not measured sibling influence processes. The present study addressed this gap by exploring the links between multiple influence processes and sibling similarities in alcohol and substance use. Method: The sample included one parent and two adolescent siblings (earlier born age: M = 17.17 years, SD = 0.94; later born age: M = 14.52 years, SD = 1.27) from 326 families. Data were collected via telephone interviews with parents and the two siblings. Results: A series of logistic regressions revealed that, after parents' and peers' use as well as other variables including parenting was statistically controlled for, older siblings' alcohol and other substance use was positively associated with younger siblings' patterns of use. Furthermore, sibling modeling and shared friends were significant moderators of these associations. For adolescents' alcohol use, the links between sibling modeling and shared peer networks were interactive, such that the associations between modeling and similarity in alcohol use were stronger when siblings shared friends. Conclusions: Future research should continue to investigate the ways in which siblings influence each other because such processes are emerging targets for intervention and prevention efforts.