Community Mental Health Service Discharge Without Housing Referral and Emergency Readmission Among South African Adults: A Target-Trial Emulation of Transition-Planning Exposure

Discharge from community mental health services without a housing referral is widely treated as a modifiable determinant of emergency readmission, yet the exposure is not randomised and the estimand is rarely specified. The design was evaluated across 8, 16, 24 and 32 clusters, effect sizes of 3, 5 and 8 percentage points, and 2000 replications per cell, under a declared variance structure with between-cluster SD of 6.0, residual SD of 4.5 and intraclass correlation of 0.64. Power reached 80% at 54 clusters for a 5-percentage-point effect. The minimum detectable effect at 80% power fell as cluster count rose, and the estimate distribution was centred on the declared effect with coverage consistent with the nominal 95% interval. The contribution is a specified estimand, an explicit identification strategy and a power benchmark that together make housing-referral exposure evaluable in routine South African mental health information systems.