Task-shifting preventive dental therapy to community health workers and untreated caries progression in rural Ugandan parishes: a stepped-wedge estimation of hygiene-therapy coverage thresholds

Task-shifting preventive dental therapy to community health workers (CHWs) is promoted as a route to extending caries control in rural African parishes, yet the coverage threshold at which such delegation produces detectable reductions in untreated caries progression has not been formally characterised. 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 54 clusters are required to detect a 5-percentage-point reduction in untreated caries progression at 80% power, and that the minimum detectable effect falls steeply as cluster count rises from 8 to 32. Kernel density and coefficient plots show that power estimates are stable across replications but that the BACIP interaction is sensitive to cluster-level heterogeneity at small cluster counts. The results imply that parish-level task-shifting trials in this setting must be powered for at least 54 clusters if a 5-percentage-point threshold is the target, and that coverage thresholds below this magnitude cannot be reliably distinguished from intraclass-correlation-driven noise at feasible cluster counts.