{ "background": "The operational efficiency of industrial machinery fleets is a critical determinant of productivity and economic output in developing industrial sectors. Current diagnostic approaches often rely on aggregate metrics or single-level analyses, which fail to account for the hierarchical structure of fleet data and contextual operational factors, leading to imprecise efficiency estimates.", "purpose and objectives": "This article presents a novel multilevel regression framework designed to provide robust efficiency diagnostics for industrial machinery fleets. The primary objective is to delineate a methodology that partitions variance in machinery performance across different organisational levels, thereby isolating controllable efficiency drivers from systemic or contextual factors.", "methodology": "The proposed methodology employs a three-level linear mixed model. Level-1 units are individual machinery operational cycles, nested within specific machines (Level-2), which are in turn nested within distinct industrial sites or companies (Level-3). The core model is specified as: $y{ijk} = \\beta{0jk} + \\beta{1}x{1ijk} + ... + e{ijk}$, where $\\beta{0jk} = \\gamma{000} + u{0jk} + v_{00k}$. Parameter estimation uses restricted maximum likelihood, with inference based on profile likelihood confidence intervals for variance components.", "findings": "Application of the framework to a case study dataset demonstrates its diagnostic capability. A key finding is that approximately 65% of the variance in fuel consumption per output unit was attributable to differences between sites (Level-3), highlighting the dominant influence of site-specific management practices over individual machine characteristics. The 95% confidence interval for this intraclass correlation was (0.58, 0.71).", "conclusion": "The multilevel regression framework provides a statistically rigorous method for diagnosing efficiency in machinery fleets, moving beyond descriptive averages to quantify the sources of performance variation. It offers a superior analytical tool for engineers and managers seeking to target interventions effectively.", "recommendations": "Practitioners should adopt this hierarchical modelling approach for fleet efficiency analysis to ensure