Quasi-Experimental Diagnostics of Water Treatment System Efficiency Gains in Senegal: A Case Study (2000–2026)

{ "background": "Evaluating the performance of large-scale water treatment infrastructure in developing regions presents significant methodological challenges. Traditional engineering assessments often lack robust counterfactuals, making it difficult to attribute changes in operational efficiency to specific interventions or management practices.", "purpose and objectives": "This case study aims to demonstrate the application of a quasi-experimental design to rigorously diagnose efficiency gains in a national water treatment system. The primary objective is to quantify the causal impact of a major rehabilitation and operator training programme on plant performance metrics.", "methodology": "A difference-in-differences (DiD) framework was employed, comparing treated plants with a matched control group of facilities not undergoing the intervention. The core statistical model is $Y{it} = \\alpha + \\beta (Treati \\times Postt) + \\gammai + \\deltat + \\epsilon{it}$, where $Y_{it}$ is the log of output per unit energy input for plant $i$ in period $t$. Robust standard errors were clustered at the plant level to account for serial correlation.", "findings": "The intervention yielded a statistically significant positive effect on system efficiency. The DiD estimator $\\beta$ was 0.18 (95% CI: 0.12, 0.24), indicating an approximate 18% increase in output per unit energy input attributable to the programme. Diagnostic tests supported the parallel trends assumption underlying the causal inference.", "conclusion": "The quasi-experimental approach provided a rigorous, evidence-based method for attributing efficiency improvements to a targeted engineering and capacity-building intervention, moving beyond descriptive performance monitoring.", "recommendations": "Adopt quasi-experimental designs for the ex-post evaluation of major infrastructure projects. Integrate the establishment of control groups and baseline data collection into the planning phases of future rehabilitation programmes to facilitate robust impact assessment.", "key words": "quasi-experimental design, difference-in-differences, water treatment efficiency, infrastructure evaluation, causal inference, Senegal", "contribution statement":