Developmental timing and cumulative exposure: a longitudinal cohort study investigating the mediating effect of negative life events in the association of parent-child separation typologies and adolescent depression in southwest China (Preprint)

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BACKGROUND In China, the predominant form of parent-child separation stems from rural-to-urban labor migration, resulting in a substantial population of left-behind children (LBC). This phenomenon is most prevalent in China's economically underdeveloped southwestern regions. These children typically display more depressive symptoms compared to their non-separated peers. The association between parent-child separation and adolescent depressive symptoms demonstrates complex temporal dynamics, with both the developmental timing ("early" or "late" childhood) and cumulative duration ("short-term" or "prolonged" separation) serving as critical moderators. Early separation experiences not only elevate depression risks but further correlate with increased exposure to negative life events during adolescence. Despite growing interest, the tripartite relationship between separation experiences, negative events, and depressive symptoms remains under-characterized in current research. OBJECTIVE This longitudinal cohort study aims to investigate the mediating role of negative life events in the association between nine parent-child separation typologies—categorized by cumulative duration (<1, 1-5, ≥5 years) and initial separation age (<3, 3-6, ≥6 years old)—and depressive symptoms among adolescents in Southwest China. METHODS Drawing data from the Children's Psychological Health Guardian Project (CPHG) – established in 2022 by the Sichuan Provincial Civil Affairs Bureau as Southwest China's largest pediatric mental health cohort – this investigation systematically collects data through 569 standardized sites (schools, clinics, etc.). Certified personnel implement data collection using a custom-developed multiplatform application (Android/iOS) incorporating data validation algorithms, integrating real-time digital monitoring with offline follow-ups. We implemented counterfactual mediation analytical frameworks using longitudinal data from two assessment waves (baseline and 6-month follow-up) involving 25,428 middle school students across Nanchong, Sichuan Province. RESULTS Of 25,428 participants, 36.98% experienced parent-child separation for more than six months (left-behind children). The marginal distribution of depression score indicated that longer separation and an earlier separation age were associated with higher depression scores. Significant mediation effects emerged across 8 typologies (ACMEs range: 0.31-0.89, p<0.05). early-onset separation (<3 years old) with intermediate duration (1-5 years) exhibited the strongest mediation effect (ACME=0.89, 95% CI: 0.43-1.38; Proportion Mediated = 66%, 95% CI: 36%-69%), followed by early-onset separation with prolonged duration (≥5 years) (ACME=0.72, 95% CI: 0.46-0.97; Proportion Mediated = 44%, 95% CI: 31%-61%). CONCLUSIONS Our findings demonstrate negative life events as a critical pathway linking early and prolonged parent-child separation to adolescent depression. Screening for negative life events combined with early psychological support and interventions should prioritize children separated before age 3 with ≥1 years exposure. CLINICALTRIAL Not applicable.