Community Health Worker Oral Hygiene Instruction Dose and Early Childhood Caries Incidence Among Malawian Preschoolers: A Target-Trial Emulation of Home-Visit Saturation Thresholds

Home-visit oral hygiene instruction delivered by community health workers is a plausible lever against early childhood caries in Malawi, but the visit dose at which a cluster-randomised programme becomes reliably detectable has not been 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 at 80% power under the declared variance structure, and that the minimum detectable effect at 80% power falls steeply as cluster count rises from 8 to 32. The intraclass correlation of 0.64 dominates the design problem: at this level of clustering, the effective sample size is a small fraction of the nominal one, and the visit-dose contrast must be carried by between-cluster variation rather than by the number of children examined. The contribution is a design specification that makes the saturation threshold estimable rather than assumed, and that identifies the cluster count at which a Malawian home-visit trial would be informative.