Peer-Led Community Mental Health Screening Fidelity and Detection of Depression Among Zimbabwean Adults: A Target-Trial Emulation of Supervision-Intensity Exposure

Peer-led community mental health screening programmes in low-resource settings depend on supervision to sustain fidelity, yet the intensity of supervision required to detect depression reliably is unknown. the present analysis characterises the operating characteristics of a before-after-control-impact design for estimating the effect of supervision intensity on depression detection by peer screeners in Zimbabwe. No observational data were used; the analysis is a design and power evaluation under a declared variance structure with 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 effect sizes of 3, 5 and 8 percentage points. The analysis indicates that 52 clusters are required to detect a 5 percentage point effect at 80% power, and that minimum detectable effects fall steeply as cluster counts rise from 8 to 32. The intraclass correlation of 0.64 dominates the design's sensitivity, so that even large effects are poorly detected with fewer than 24 clusters. The contribution is a design template that makes supervision-intensity effects estimable in peer-led screening programmes without overstating what small district-level evaluations can detect.