demonstrating that parental smoking is a risk factor for adolescent smoking (59,65). However, one study found that the effect of parental disapproval both in smoking and nonsmoking parents was stronger and more robust than that of parental smoking and even attenuated the effect of peer smoking, suggesting that parental disapproval makes adolescents more resistant to peer smoking (66). However, it remains unclear to what extent this is pure environment and passive gene-environment correlation. The presence of gene-environment correlation would imply that non-smoking parents pass on their “non-smoking” genes but also create a non-smoking environment. Siblings also influence the initiation and escalation of cigarette use, such that having older siblings who smoke increases a child’s risk of smoking even after adjusting for parents’ smoking (67). Risk of initiation increases substantially as the number of smokers in an adolescent’s environment increases, with adolescent females more likely to smoke than adolescent males (57,68). Besides their smoking behavior, social connectedness between siblings appears to moderate shared environmental influences on smoking frequency and any subsequent changes on smoking frequency (69). Given that few longitudinal studies have examined how these family influences shape cigarette use following experimentation and initiation, information that could inform the development of
