The association may not be causal and could be explained common underlying factors for smoking and SRB. Thus, it is important to enhance the understanding of the role of familial factors, such as childhood environment or dispositional genetic factors, which might underlie these relationships. One approach is to study these associations among discordant twin pairs. By design, this approach controls for potential familial confounds shared by the twins such as family structure, socioeconomic status, and medical history. The first aim of this study was to examine the developmental relationships of early–onset tobacco use in adolescence with SRB (intentional self-injury, suicidal ideation) in young adulthood. The second aim was to test whether these relationships are replicated when controlling for shared genetic and other familial influences.
