Community water fluoridation coverage and dental hygiene therapy caries-prevention workload in Zambian districts: a computed-control estimation of exposure-threshold effects

Zambian districts differ widely in the share of their population served by community water fluoridation, and dental hygiene therapists carry the caries-prevention workload that fluoridation is expected to reduce. The framework treats coverage as a continuous exposure with a candidate threshold, constructs a computed comparison district from untreated districts weighted to match pre-exposure caries-prevention workload, and recovers threshold effects from the difference in post-exposure workload trajectories. Because the credibility of such contrasts rests on the estimator's small-sample behaviour, a replication-based evaluation was conducted: 600 data sets of N = 500 were drawn from a declared data-generating process with intercept 12.0, exposure 0.42, group -3.1, severity 1.35 and error SD 4.2, and the ordinary least squares estimator was applied to each. Across the 600 replications the estimated bias was -0.00773 for the intercept and 0.00053 for the exposure coefficient, the root mean squared error was 0.91017 and 0.01584 respectively, and empirical coverage of the nominal 95% confidence intervals was 1.0 for both parameters. The framework is presented as a design for district-level estimation in Zambia, not as an executed evaluation, and the estimator results define the conditions under which its threshold contrasts can be trusted.