Task-Sharing Supervision Intensity and Community Mental Health Worker Diagnostic Concordance in Ugandan Primary Care: A Mixed-Methods Implementation Trial

Community mental health workers (CMHWs) in task-sharing programmes make diagnostic decisions that determine access to care, yet the supervision intensity required to sustain diagnostic concordance with specialist assessment remains unspecified. The trial was designed as a before-after-control-impact (BACI) evaluation with a declared variance structure (between-cluster SD = 6.0, residual SD = 4.5, intraclass correlation = 0.64) and power estimated across 2000 design cells. The design achieved 80% power to detect a 5 percentage-point concordance difference with 54 clusters. Quantitative concordance estimates were complemented by semi-structured interviews with CMHWs and supervisors, analysed thematically. The results indicate that concordance improved with supervision intensity but with diminishing returns beyond fortnightly contact, and that the BACI estimator was sensitive to cluster-level heterogeneity. Supervision intensity should be treated as a design parameter with a defined operating range rather than as a monotonic good, and it specifies the cluster counts and effect sizes at which BACI evaluation of supervision reforms is adequately powered.