Understanding Social Influence of Non-Suicidal Self-Injury: The Interplay of Peer Networks and Adolescent Behavior.

Adolescents' non-suicidal self-injury (NSSI) could be influenced by their friends' NSSI and by their own social position within peer networks. However, prior research has examined these effects separately and has primarily focused on middle-to-late adolescence. It remains unclear how friends' NSSI relates to adolescents' NSSI under different social positions and how these effects differ across different age stages. This study examined both the independent and interactive effects of the number of friends engaging in NSSI, the number of claiming friends, and the extent of bridging different peer groups on adolescents' NSSI behaviors within classroom-based social networks. The sample included 9581 Chinese adolescents (44.6% girls, Mage = 13.72, SD = 1.87) from 221 classroom-based friendship networks, comprising 4248 early adolescents and 5333 middle-to-late adolescents. Social network analyses were used to extract network-related indicators, while general linear mixed models were employed to test the hypotheses. Results revealed that adolescents with more friends engaging in NSSI faced a higher risk of engaging in NSSI themselves; however, this risk decreased for adolescents with more claiming friends, irrespective of age. Adolescents who acted as bridges between different peer groups and had an above-average number of claiming friends were more likely to engage in NSSI, but this was only the case in early adolescence. These findings suggest NSSI can spread through friendship networks, with social connections influencing how likely adolescents are to be affected. Incorporating social network assessments into mental health screenings might facilitate early identification and prevention of NSSI among youth.