{ "background": "Process-control systems are critical for the operational efficiency and safety of civil engineering infrastructure, yet rigorous, field-based evaluations of their cost-effectiveness in developing economies are scarce. Policy decisions regarding their adoption are often made without robust empirical evidence tailored to local contexts.", "purpose and objectives": "This policy analysis article develops and demonstrates a novel quasi-experimental methodology to diagnose the cost-effectiveness of process-control systems in a West African context. It aims to provide a replicable framework for generating evidence to inform procurement and maintenance policies.", "methodology": "A difference-in-differences design is employed, comparing cost and performance metrics between treatment groups (infrastructure with new process-control systems) and control groups (infrastructure with legacy systems) before and after intervention. The core statistical model is a fixed-effects regression: $Y{it} = \\alpha + \\beta (Treatmenti \\times Postt) + \\gamma X{it} + \\deltai + \\lambdat + \\epsilon_{it}$, where robust standard errors are clustered at the facility level to account for serial correlation.", "findings": "The diagnostic application indicates a statistically significant reduction in operational expenditure, with a point estimate suggesting an average decrease of approximately 18% (95% CI: 12% to 24%) for treated facilities relative to controls. However, the analysis reveals substantial heterogeneity in effectiveness linked to pre-existing maintenance regimes.", "conclusion": "The quasi-experimental design provides a technically sound and policy-relevant framework for evaluating engineering systems in real-world settings. It confirms that while process-control systems can be highly cost-effective, their benefits are not automatic and are contingent on complementary institutional factors.", "recommendations": "Policy for engineering system procurement should mandate pilot evaluations using such quasi-experimental diagnostics prior to large-scale rollout. Investment should be coupled with capacity-building programmes to standardise maintenance protocols, thereby ensuring realised benefits align with projected outcomes.", "key words": "cost-effectiveness, process control, quasi-experimental design, infrastructure policy, difference-in