"background": "Industrial machinery fleet reliability is a critical determinant of productivity and economic growth in developing economies. In the context of Ethiopia, systematic, longitudinal evaluations of reliability interventions for such fleets are scarce, limiting evidence-based asset management. ", "purpose and objectives": "This study aims to methodologically evaluate the application of a difference-in-differences (DiD) model for quantifying the causal impact of a national preventive maintenance programme on the operational reliability of industrial machinery fleets. It compares outcomes between treated and control fleets over an extended period. ", "methodology": "A comparative DiD analysis was conducted using panel data from machinery fleets in the cement and textile manufacturing sectors. The core statistical model is Y{it = \0 + \1 + \2 + \ (\) +, where Yit is the monthly reliability index. Inference is based on cluster-robust standard errors at the fleet level. ", "findings": "The analysis indicates a statistically significant positive treatment effect. The DiD estimator, \, shows that the programme increased the mean reliability index by 17. 3 percentage points (95% CI: 12. 1 to 22. 5). The parallel trends assumption, tested using lead variables, was not violated. ", "conclusion": "The DiD framework provides a robust methodological approach for isolating the causal effect of engineering interventions on fleet reliability in an observational setting. The significant positive result underscores the efficacy of structured preventive maintenance. ", "recommendations": "Policymakers and industrial asset managers should adopt quasi-experimental evaluation designs like DiD for programme assessment. The preventive maintenance protocol studied should be considered for broader national rollout, with continuous data collection to refine the model. ", "key words": "difference-in-differences; machinery reliability; preventive maintenance; causal inference; industrial engineering
Assefa et al. (Thu,) studied this question.
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