"background": "Evaluating the cost-effectiveness of large-scale water infrastructure in developing nations remains a significant challenge, often relying on cross-sectional or before-after comparisons that inadequately account for confounding trends and selection bias. ", "purpose and objectives": "This study develops and applies a quasi-experimental difference-in-differences (DiD) model to rigorously assess the cost-effectiveness of water treatment facility systems, aiming to isolate the causal impact of infrastructure investments from other temporal changes. ", "methodology": "A panel dataset was constructed for treatment and control groups of communities. The core DiD model is specified as Y{it = \0 + \1 + \2 + \ (\) +, where Yit is the cost-per-cubic-metre metric. Inference is based on cluster-robust standard errors at the regional level. ", "findings": "The DiD estimator (\) indicates a statistically significant reduction in average unit costs of 18. 2% (95% CI: 12. 5% to 23. 9%) attributable to the new infrastructure programme, after controlling for underlying trends common to both groups. ", "conclusion": "The DiD framework provides a more robust methodological approach for cost-effectiveness analysis in civil engineering projects than conventional methods, effectively accounting for unobserved confounders that evolve linearly over time. ", "recommendations": "Infrastructure planning authorities should adopt quasi-experimental evaluation designs, particularly DiD models, for the ex-post assessment of major capital projects to inform future investment prioritisation and improve accountability. ", "key words": "cost-benefit analysis, quasi-experimental design, infrastructure evaluation, water treatment, econometric modelling", "contribution statement": "This paper provides the first application of a difference-in-differences model to evaluate the cost-effectiveness of water treatment infrastructure in a
Tadesse et al. (2014) studied this question.