Dental hygiene therapy–led minimally invasive caries management and out-of-pocket expenditure in Rwandan district hospitals: a target-trial emulation of clinician decision thresholds under fee-for-service constraints

Fee-for-service payment in Rwandan district hospital dental clinics creates a structural tension between minimally invasive caries management and household out-of-pocket expenditure. Because no primary observational data were available, the study characterises the operating characteristics of a before-after-control-impact design capable of detecting threshold shifts under a declared variance structure. The design assumed a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5, and an intraclass correlation of 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. Under these parameters, 56 clusters were required to detect a 5-percentage-point effect at 80% power. Plausible district-level clustering substantially constrains the detectable threshold shift, and that studies of payment reform in similar settings must be sized accordingly.