Community Mental Health Team Co-Location With Primary Care and Detection of Psychosis Among South African Adults: A Target-Trial Emulation of Referral-Pathway Exposure

Co-locating community mental health teams with primary care is widely promoted as a way to shorten untreated psychosis, yet the referral-pathway exposure it creates is difficult to evaluate because teams are placed where need and infrastructure already differ. the present analysis treats co-location as a point exposure embedded in a referral pathway and specifies a target-trial emulation that estimates its effect on detection of first-episode psychosis among South African adults. The estimand is the counterfactual difference in one-year detection under immediate co-location versus no co-location, with eligibility, treatment strategies, assignment, time zero, follow-up and outcome defined explicitly. Because no observational data are analysed here, the design's operating characteristics are characterised under a declared variance structure: between-cluster standard deviation 6.0, residual standard deviation 4.5 and intraclass correlation 0.64. Power was estimated across 2000 replications per design cell for cluster counts of 8, 16, 24 and 32 and effects of 3, 5 and 8 percentage points. Under this structure, 52 clusters are required for 80% power at a 5-percentage-point effect. The contribution is a pre-specified, auditable protocol that separates the causal question from the clustering that dominates cluster-referral designs, and that names the conditions under which co-location effects can and cannot be identified.