{ "background": "District hospitals in sub-Saharan Africa face systemic challenges affecting clinical care quality. Robust quantitative methods are required to evaluate health systems interventions, moving beyond descriptive reporting to causal inference.", "purpose and objectives": "This study aimed to quantify the causal effect of a multifaceted health systems strengthening intervention on clinical outcomes in district-level facilities. The primary objective was to estimate the intervention's impact on in-hospital mortality using a quasi-experimental design.", "methodology": "We conducted a controlled, longitudinal intervention study. A difference-in-differences model was employed, comparing changes in outcomes between 12 intervention and 15 matched control hospitals over multiple periods. The core estimating equation was $Y{it} = \\alpha + \\beta (Interventioni \\times Postt) + \\gammai + \\deltat + \\epsilon{it}$, where $Y{it}$ is the mortality rate, $\\gammai$ are hospital fixed effects, and $\\delta_t$ are time fixed effects. Inference was based on cluster-robust standard errors.", "findings": "The intervention was associated with a statistically significant reduction in risk-adjusted in-hospital mortality of 4.2 percentage points (95% CI: -6.1, -2.3). This represents a relative decline of approximately 18% from the pre-intervention baseline. No significant effects were detected on secondary outcomes of average length of stay or readmission rates.", "conclusion": "The implemented health systems package effectively reduced mortality in the intervention hospitals. The difference-in-differences approach provided a rigorous framework for attributing this change to the intervention within a real-world, non-randomised setting.", "recommendations": "Policy makers should consider scaling the core components of the intervention, particularly those targeting clinical decision support and essential resource availability. Future evaluations should incorporate cost-effectiveness analyses and explore mechanisms of effect through mixed-methods research.", "key words": "health systems strengthening, quasi-experimental design, causal inference, hospital mortality, sub-Saharan Africa, health policy