Community-Based Trauma Mental Health Task-Sharing Supervision Dosage and Post-Traumatic Stress Symptom Persistence Among Ghanaian Lay Counsellors: A Stepped-Wedge Analysis of Supervision Interval Thresholds

Supervision dosage in community-based trauma mental health task-sharing is typically set by convention rather than by evidence about the minimum interval at which lay counsellor cohorts can be statistically distinguished from comparison cohorts. 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 found that 54 clusters were required to detect a 5-percentage-point effect at 80% power under this variance structure, and that power at 8, 16 and 24 clusters remained below the conventional threshold for all three effect sizes. The minimum detectable effect at 80% power fell steeply between 24 and 32 clusters but remained above 5 percentage points at 32 clusters. These results imply that supervision interval thresholds cannot be reliably estimated in the small district-level cohorts that characterise Ghanaian task-sharing programmes, and that the field should treat supervision dosage as a design parameter to be powered prospectively rather than a programme feature to be evaluated post hoc.