Community water fluoridation coverage and dental hygiene therapy caries-arrest workload in South African municipalities: a difference-in-differences analysis of policy adoption timing

South African municipalities have adopted community water fluoridation (CWF) at different times, creating a natural policy experiment in which dental hygiene therapy caries-arrest workload can be compared across early-adopting and late-adopting jurisdictions. Because no observational CWF workload data were available for this analysis, the study characterises the behaviour of the ordinary least squares (OLS) DiD estimator under a declared data-generating process calibrated to plausible municipal parameters: intercept 12.0, exposure 0.42, group −3.1, severity 1.35, and error SD 4.2. A replication-based evaluation was conducted with 600 data sets of N = 500 drawn under seed 1925419919. The estimator recovered the exposure coefficient with negligible bias (−0.00068) and RMSE of 0.01584, and nominal 95% confidence intervals achieved 1.0 coverage for both the intercept and the exposure coefficient. The results indicate that the DiD specification is adequately powered and correctly calibrated for the proposed municipal workload comparison, and they support proceeding to empirical estimation once administrative CWF and workload data are assembled.