Protocol for a systematic review of the development of depression among adolescents and young adults: psychological, biological, and contextual perspectives around the world

Background: Depression is a leading contributor to disability-adjusted life-years because of early onset and chronicity throughout the lifecycle. It is crucial to identify early predictors of depression among adolescents and young people to effectively target prevention. A gap in the literature is a comprehensive systematic review of predictors of depression among adolescents around the globe, especially in low- and middle-income countries LMICs. This review aims to identify evidence for biological, psychological, and contextual risk factors for the development of depression among adolescents and young adults (10-24 years of age) in high-income countries (HICs) and LMICs, ultimately contributing to (a) identification of potential mechanisms underlying depression development, (b) selection of common risk and protective factors as targets for detection, and (c) refinement of risk models that can be evaluated through existing cohorts in HICs and LMICs. Methods: This review will follow the Population, Exposure, Comparison, Outcome (PI(E)C0) model and adheres to the PRISMA-P guidelines. A search strategy was developed by a multidisciplinary research consortium. Seven databases (MEDLINE via Ovid, PsycINFO, Cochrane Database of Systematic Reviews, Web of Science, Lilacs, African Journals Online, Global Health) will be searched to identify articles. Independent raters will screen and retrieve articles for inclusion, conduct quality ratings, and extract data. The Systematic Assessment of Quality in Observational Research adapted for Cultural Psychiatry Epidemiology (SAQOR-CPE) will be used to assess quality of observational studies. We will assess for publication bias using funnel plots and statistical methods. We will use narrative synthesis to present results, addressing the study's objectives following the Cochrane Handbook guidelines. Meta-analyses will be used to report summary statistics for association of risk factors with development of depression. Discussion: This systematic review will summarize evidence-based research that examines the psychological, biological, and contextual factors contributing to the onset of depression in adolescents across the globe. Results will support the development of a model that can be evaluated in existing cohorts around the world.