The developmental pathways linking early conduct problems (CP) to later psychological distress (PSYD) remains insufficiently understood, particularly mediating role of peer problems (PP). This study examines how CP influence adolescent PSYD directly and indirectly through PP using longitudinal data from an Australian cohort. Data were drawn from Waves 6-8 (ages 10-15) and Wave 9C2 (ages 17-18) of the Longitudinal Study of Australian Children (LSAC), including 1850 participants with complete data. CP and PP were assessed using the Strengths and Difficulties Questionnaire (SDQ), while PSYD was measured via the Kessler PSYD Scale (K10). Structural Equation Modelling (SEM) with Weighted Least Squares Mean and Variance Adjusted (WLSMV) estimation tested direct and indirect pathways, with PP as a mediator. Adolescents with persistent or severe CP and PP were more likely to report severe PSYD at ages 17-18. SEM showed that PP significantly mediated the relationship between CP and PSYD, with direct effects of CP largely nonsignificant. The strongest indirect effect was observed for severe CP at Wave 8 (β̂ = 0.147, p=0.004), followed by borderline CP at Wave 8 (β̂ = 0.107, p=0.006), severe CP at Wave 7 (β̂ = 0.094, p=0.004), and borderline CP at Wave 6 (β̂ = 0.027, p=0.006). PP also showed strong temporal stability across waves. Findings underscore the role of PP in the developmental trajectory from early CP to later PSYD, highlighting the need for early intervention targeting behavioural and peer-related difficulties.

Social anxiety disorder (SAD) frequently co-occurs with major depressive disorder (MDD). We examined the prevalence and clinical correlates of SAD across three heterogeneous MDD cohorts. Secondary analyses were conducted in adult (CO-MED: n=482; GSRD: n=1398) and late-life (IRL-GREY: n=438) patients. SAD was assessed dimensionally (PDSQ) and categorically (MINI; SCID-1). Cohort-specific instruments were used to assess depressive severity (QIDS; MADRS), suicidality (CHRT; MADRS; SIS) and hypomanic symptoms (ASRM; YMRS). In late-life depression, neurocognitive tests were administered. Multivariate models were adjusted for depression and anxiety levels. SAD prevalence varied markedly by samples and diagnostic definitions (CO-MED: 46.7% with PDSQ≥6; 17.0% with PDSQ>12; GSRD: 3.0%; IRL-GREY: 8.7%). Across cohorts, SAD was associated with earlier MDD onset (CO-MED: p<0.001 d=-0.36; GSRD: p=0.014 d=-0.39; IRL-GREY: p=0.002 d=-0.54) and greater anxiety comorbidity (CO-MED: GAD: p<0.001 d=1.24; panic: p<0.001 d=1.29; GSRD: GAD: p<0.001; panic: p<0.001; IRL-GREY: agoraphobia: p<0.001). After controlling for depression and anxiety levels, SAD was linked to higher suicide risk in both adult cohorts (CO-MED: OR 1.04 (1.01-1.08); GSRD: OR 1.29 (1.04-1.64)) and to lower 6-week remission in CO-MED cohort (OR 0.51 (0.29-0.91)). In MDD, SAD has consistent associations with earlier illness onset and anxiety burden, modest associations with suicidality and antidepressant outcomes, and reduced impact in late life.