There are several possible reasons for the strong relationship between peer alcohol use and adolescent alcohol use. Peers may influence adolescent drinking behaviour by serving as role models and by influencing attitudes towards alcohol. They can also facilitate access to and encouragement of alcohol use [10,11]. Alternatively, given that adolescents are involved actively in selecting and maintaining friendships, they may select friends with similar drinking habits to themselves (peer selection [12,13]). It is likely that the association between friends' and adolescent alcohol use is due to both peer selection and peer influence. Other factors, including cultural norms, neighbourhood influences, school and larger peer networks, will also have an impact [5,14,15].
