{ "background": "Persistent inefficiencies in manufacturing systems constrain industrial development in many African economies. A robust, quantitative diagnostic framework for cost-effectiveness is required to inform targeted engineering and managerial interventions.", "purpose and objectives": "This case study develops and applies a panel-data econometric methodology to diagnose the cost-effectiveness of manufacturing systems, using the Ethiopian context as an empirical testbed. The objective is to quantify production inefficiencies and identify their key determinants.", "methodology": "A case study approach utilising an unbalanced panel dataset from multiple manufacturing plants. The core analytical model is a generalised Cobb-Douglas cost function estimated via fixed-effects regression with robust standard errors: $\\ln C{it} = \\beta0 + \\betay \\ln Y{it} + \\sumk \\betak \\ln w{kit} + \\alphai + \\epsilon{it}$, where $\\alphai$ captures plant-specific inefficiency. Diagnostic tests for heteroskedasticity and serial correlation were conducted.", "findings": "The model reveals significant latent cost inefficiencies, with an average plant-specific effect, $\\alpha_i$, accounting for a cost premium of approximately 18% relative to the estimated efficient frontier. Inferences indicate that scale of operation and technology vintage are statistically significant determinants (p < 0.01), whereas input price variation showed less explanatory power.", "conclusion": "The panel-data estimation provides a technically rigorous diagnostic tool, confirming substantial and heterogeneous cost inefficiencies within the studied manufacturing systems. The methodology successfully isolates persistent plant-level effects from transient fluctuations.", "recommendations": "Manufacturing plant managers should prioritise audits focused on scale utilisation and technology upgrading. Policymakers are advised to support benchmarking initiatives using similar panel-data frameworks to identify sector-wide inefficiency patterns.", "key words": "cost efficiency, panel data, econometric modelling, manufacturing diagnostics, industrial engineering, fixed effects", "contribution statement": "This study provides a novel application of panel-data econometrics as an engineering