{ "background": "Transport maintenance depots in Ghana face systemic inefficiencies, leading to suboptimal asset availability and high operational costs. Traditional performance measurement frameworks often fail to account for the complex, multi-level variability inherent in depot operations and supply chains, resulting in unreliable yield estimates.", "purpose and objectives": "This case study aims to methodologically evaluate the application of a Bayesian hierarchical model for quantifying and improving yield within these depot systems. The objective is to assess the model's capacity to provide robust, actionable insights by formally incorporating operational uncertainty and hierarchical data structures.", "methodology": "A case study methodology was employed, analysing operational data from a network of depots. The core statistical model is a Bayesian hierarchical linear model: $y{ij} \\sim \\text{Normal}(\\alphaj + \\beta X{ij}, \\sigma^2)$, $\\alphaj \\sim \\text{Normal}(\\mu{\\alpha}, \\tau^2)$, where $y{ij}$ is the yield for observation $i$ in depot $j$, $\\alphaj$ are depot-specific intercepts, and $X{ij}$ denotes covariates. Inference was performed using Hamiltonian Monte Carlo.", "findings": "The model successfully identified significant inter-depot performance variation, with the posterior distribution for the hyperparameter $\\tau$ indicating a standard deviation of 12.7% in baseline yield between depots (95% credible interval: 9.2% to 16.1%). This quantifiable heterogeneity, previously unmeasured, highlights specific depots as primary targets for intervention. The analysis demonstrates the model's utility for probabilistic performance ranking and root-cause diagnosis.", "conclusion": "The Bayesian hierarchical model provides a statistically rigorous framework for yield analysis in maintenance depots, effectively quantifying uncertainty and isolating sources of variation. It represents a superior methodological approach for engineering management in data-scarce, high-variability environments.", "recommendations": "Implement the modelling framework as a standard diagnostic tool for depot network performance reviews.