{ "background": "Public health surveillance is a cornerstone of effective health systems, yet its methodological rigour and efficiency in resource-constrained settings require systematic assessment. In Nigeria, numerous interventions have aimed to strengthen surveillance, but a consolidated quantitative synthesis of their impact is lacking.", "purpose and objectives": "This meta-analysis aims to methodologically evaluate the application of difference-in-differences (DiD) models in assessing the efficiency gains of public health surveillance interventions in Nigeria and to synthesise the pooled effect estimates from these studies.", "methodology": "A systematic search identified peer-reviewed studies and grey literature employing DiD designs to evaluate surveillance system interventions. Studies were assessed for methodological quality. The primary pooled effect was estimated using a random-effects meta-analysis model. The core DiD model for included studies is formalised as $Y{it} = \\beta0 + \\beta1 \\text{Treat}i + \\beta2 \\text{Post}t + \\delta (\\text{Treat}i \\times \\text{Post}t) + \\epsilon_{it}$, where $\\delta$ is the key parameter of interest. Heterogeneity was quantified using the I² statistic.", "findings": "The synthesis of estimates indicates a statistically significant positive effect of methodological improvements on surveillance efficiency. The pooled estimate for timeliness of outbreak reporting showed a mean reduction of 3.2 days (95% CI: -4.1 to -2.3). However, considerable heterogeneity was observed (I² = 78%), suggesting variability in intervention effectiveness and implementation contexts.", "conclusion": "The application of DiD models provides robust evidence for efficiency gains in surveillance systems, though effect sizes are heterogeneous. Methodological rigour in design and reporting of such evaluations requires strengthening to enhance comparability and generalisability.", "recommendations": "Future evaluations should pre-specify DiD model assumptions and report parallel trends tests. Policymakers should invest in integrated digital reporting platforms, as these were a common component in