Community Mental Health Service Peer-Support Worker Caseload Composition and Psychiatric Emergency Relapse in Ghanaian Community Teams: A Target-Trial Emulation of Relapse Surveillance Exposure

Peer-support workers have become a routine component of community mental health teams in Ghana, yet the design of their caseloads remains unstandardised and the surveillance function they perform is rarely modelled explicitly. the present analysis treats peer-support caseload composition as a form of relapse surveillance exposure and asks how the before-after-control-impact (BACI) estimator, widely used to evaluate team-level caseload reforms, behaves when the outcome is a rare psychiatric emergency relapse and the exposure is assigned at the cluster level. No observational data are used or claimed. The analysis characterises the operating characteristics of the BACI design under a declared variance structure with a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.64. Power was estimated across 2000 design cells spanning cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Under this variance structure, 52 clusters are required to detect a 5 percentage point reduction in relapse at 80% power, a requirement that exceeds every cluster count examined. The surveillance-exposure framing clarifies why caseload reforms in Ghanaian community teams are difficult to evaluate with the designs currently in use, and it specifies the conditions under which a BACI evaluation of peer-support caseload composition would yield interpretable estimates.