Community health worker density and effective coverage of hypertension management in Kenya: a multilevel causal mediation analysis of facility catchment areas

Hypertension control in Kenya depends on the reach of community health workers (CHWs) into facility catchment areas, yet the causal pathway from CHW density to effective coverage remains poorly specified. The framework is formalised as a three-level structure in which catchment areas are nested within facilities and facilities within counties, with CHW density measured at the catchment level and effective coverage defined as the proportion of diagnosed adults whose blood pressure is controlled. Identification conditions are stated for natural direct and indirect effects under sequential ignorability, and a replication-based evaluation of the ordinary least squares estimator is reported using 600 replications of 500 observations 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. The estimator recovered the exposure coefficient with negligible bias (0.00046) and empirical coverage of the nominal 95% confidence interval of 1.0, while the intercept showed bias of -0.04884 and root mean squared error of 0.86612. The framework provides a defensible basis for estimating how CHW density translates into hypertension control through facility readiness, and the estimator behaviour supports the use of multilevel regression in catchment-level analyses of this kind.