Dental hygiene therapy–delivered oral-health education and dental caries incidence in Ugandan refugee settlements: a cluster-randomised trial of lay-cadre task-shifting

Task-shifting oral-health education to lay cadres supervised by dental hygiene therapists has been proposed as a means of extending caries prevention into Ugandan refugee settlements, but the cluster-randomised designs used to evaluate such programmes are rarely powered with explicit attention to the intraclass correlation induced by settlement-level clustering. 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 caries incidence at 80% power, a requirement that exceeds the cluster counts typically available to settlement-level trials. Minimum detectable effect curves and coefficient plots show that the before-after-control-impact interaction is sensitive to cluster count at small effect sizes and that estimates at 8 clusters carry confidence intervals wide enough to span the null. The contribution is a design-stage quantification of what lay-cadre task-shifting trials in refugee settings can and cannot establish, and a specification of the cluster counts at which such trials become informative.