{ "background": "The selection of process-control system methodologies for industrial infrastructure in developing economies is often based on theoretical models or vendor specifications, with limited empirical evidence from field trials to guide cost-effectiveness decisions.", "purpose and objectives": "This study aimed to empirically compare the cost-effectiveness of three prevalent process-control system methodologies—centralised, distributed, and hybrid architectures—within the context of industrial infrastructure projects.", "methodology": "A randomised field trial was conducted across multiple infrastructure sites. Projects were randomly assigned a control methodology. Cost-effectiveness was measured as a function of capital expenditure (CAPEX), operational expenditure (OPEX) over a defined period, and system uptime. The primary analysis used a generalised linear model: $\\text{Cost-Effectiveness Index}i = \\beta0 + \\beta1 \\text{Methodology}i + \\beta2 \\text{Project Scale}i + \\epsilon_i$, with inference based on robust standard errors.", "findings": "The distributed control system architecture demonstrated superior cost-effectiveness, with a statistically significant 18.7% lower combined CAPEX and OPEX compared to the centralised approach (95% CI: 12.3% to 25.1%). The hybrid methodology showed intermediate performance, not statistically different from the distributed system in overall cost but with higher variability in maintenance costs.", "conclusion": "For the industrial infrastructure context studied, distributed control architectures offer a more cost-effective solution than traditional centralised systems, primarily through reduced operational expenditures.", "recommendations": "Project planners and engineers should prioritise distributed control system methodologies for similar medium-scale industrial infrastructure. Further research should investigate the scalability of these findings to larger, more complex installations.", "key words": "process control, industrial automation, cost-benefit analysis, randomised controlled trial, infrastructure engineering, systems engineering", "contribution statement": "This study provides the first randomised field-trial evidence comparing the real-world cost-effectiveness of major process-control methodologies in an African industrial infrastructure setting