Which factors mediate the effect of childhood socioeconomic disadvantage on mental health in young adulthood? A protocol for a target trial emulation using linked administrative data from New South Wales, Australia.

introductionEarly-life socioeconomic status (SES) increases the risk of poor mental health outcomes in adulthood. However, the mechanistic pathways underlying this relationship remain poorly understood. While addressing socioeconomic inequalities remains a long-term goal, identifying specific mediating pathways could reveal more immediate opportunities for effective interventions. METHODS AND ANALYSIS: Using linked administrative data from New South Wales, Australia (1990-2022), we will emulate a target trial examining the relationship between SES at birth and acute mental health admissions and presentations between the ages of 18 and 25 years. An interventional mediation analysis will be used to examine the effect of multiple mediating pathways, including education, housing stability, child protection contact, parental incarceration and justice system involvement, on the outcome. The analysis will estimate direct and indirect interventional effects, quantifying how much of the SES-mental health relationship could be modified by interventions on specific mediators. ETHICS AND DISSEMINATION: This study has received ethics approval from the University of Newcastle (H-2024-0015) and Aboriginal Health and Medical Research Council (2265/24) Human Research Ethics Committees. All dissemination activities will be conducted in accordance with data access agreements and following approval from all relevant data custodians (New South Wales Health System Data Services). Key findings will be communicated to relevant government agencies and policymakers through policy briefs and stakeholder meetings, and publication in appropriate academic journals.