Dental hygiene therapy radiograph referral authority and caries diagnostic yield in Ghanaian polyclinics: a stepped-wedge evaluation of delegated prescribing

Ghanaian polyclinics have begun delegating dental radiograph referral authority to dental hygiene therapists, but the diagnostic yield of that delegation cannot be estimated credibly from small, clustered facility samples without knowing the design's operating characteristics. the present analysis evaluates the before-after-control-impact (BACI) estimator for a stepped-wedge evaluation of delegated prescribing, using a replication-based design study rather than observational data. Under a declared variance structure with between-cluster standard deviation 6.0, residual standard deviation 4.5 and intraclass correlation 0.64, 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.54 clusters are required to detect a 5-percentage-point effect at 80% power, that the minimum detectable effect falls steeply as clusters increase from 8 to 32, and that the BACI interaction remains estimable at the upper cluster counts despite the high intraclass correlation. The contribution is a design-based calibration of what a Ghanaian polyclinic evaluation of delegated radiograph referral can and cannot detect, and a demonstration that the BACI estimator's power profile, not the substantive effect, governs whether the policy question is answerable at all.