"background": "Waterborne diseases remain a significant public health challenge in many regions, with infrastructure resilience being a critical engineering concern. Systematic evaluation of structural and operational interventions in water treatment systems is required to quantify their effectiveness in mitigating public health risks. ", "purpose and objectives": "This case study aims to methodologically evaluate the application of a quasi-experimental difference-in-differences (DiD) model to assess the risk reduction achieved by a major rehabilitation programme applied to a subset of water treatment facilities. The objective is to demonstrate the model's utility for isolating the causal effect of engineering interventions from secular trends. ", "methodology": "A longitudinal panel dataset of facility performance and regional health outcomes was constructed. The core DiD model is specified as Y{it = \0 + \1 + \2 + \ (\) +, where Yit is the log-transformed incidence of waterborne disease. Inference is based on cluster-robust standard errors to account for serial correlation. ", "findings": "The DiD estimator \ was -0. 18, indicating a statistically significant reduction in log disease incidence attributable to the intervention. The implied average treatment effect corresponds to an approximate 16% reduction in reported cases in regions served by rehabilitated facilities relative to the control group, with a 95% confidence interval of -0. 31, -0. 05. ", "conclusion": "The difference-in-differences approach provides a robust methodological framework for causal inference in post-hoc evaluation of engineering infrastructure projects, effectively controlling for common temporal shocks. ", "recommendations": "Engineering project evaluations should incorporate quasi-experimental designs like DiD where randomised control trials are impractical. Practitioners should prioritise the collection of longitudinal data from both intervention and control facilities to enable such analyses. ", "key words": "causal
Mwangi et al. (Fri,) studied this question.