District Hospital Trauma Mental Health Screening Uptake After Community Health Worker Home Visit Intervals and Post-Traumatic Stress Disorder Detection in Malawian Clinics: A Stepped-Wedge Implementation Trial

Stepped-wedge and before–after–control–impact (BACI) designs are increasingly proposed for evaluating health-system interventions in low-resource settings, yet their operating characteristics are rarely characterised before fieldwork begins. No observational data were used or claimed. The analysis characterised the operating characteristics of the BACI estimator 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 0.640. 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 indicated that 54 clusters would be required to detect a 5-percentage-point effect at 80% power. The intraclass correlation of 0.64 dominated the variance budget, and the minimum detectable effect at 80% power fell steeply as cluster count rose from 8 to 32. The results imply that the planned trial as originally conceived is underpowered at feasible cluster counts and that the design should be re-specified before implementation.