Depression as a Predictor Between Social Isolation and Risky Behaviour Among Out-of-School Adolescents

Out-of-school adolescents represent a globally vulnerable population whose mental health and behavioural outcomes remain under-mapped in the evidence base. This scoping review synthesised available evidence on whether depression functions as a predictor or mediator in the relationship between social isolation and risky behaviour among out-of-school adolescents aged ten to nineteen years. The review followed the Arksey and O'Malley five-stage framework, enhanced by Levac and colleagues and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews. Four electronic databases (PubMed, PsycINFO, CINAHL and Scopus) were searched for peer-reviewed publications between 2014 and 2025, supplemented by hand-searching of reference lists and grey literature. Two reviewers independently screened records and charted data using a standardised form. Fifty-four studies met the inclusion criteria, spanning twenty-eight countries across low, middle and high-income settings. Thematic synthesis identified four interrelated domains: measurement heterogeneity for social isolation; high prevalence of depression among socially isolated out-of-school youth; clustering of risky behaviours including substance use, sexual risk-taking, delinquency and self-harm; and consistent statistical evidence that depression operates as a mediator or predictor in the isolation-behaviour pathway. Longitudinal studies provided temporal evidence supporting the predictive role of depression, while cross-sectional studies predominantly demonstrated mediating effects. Moderating factors included sex, age subgroup, family connectedness, peer network characteristics and neighbourhood safety. The evidence base is constrained by definitional variability, reliance on self-report measures and limited representation of low and middle income country contexts. The findings indicate that targeted screening and management of depression among socially isolated out-of-school adolescents may reduce engagement in risky behaviours, and that integrated adolescent mental health programmes should be prioritised within national public health strategies.