Why has Nigerias neonatal mortality decline stalled? An ecological analysis of public health financing and macroeconomic instability, 1990-2024

Background. Nigeria carries one of the world's largest burdens of neonatal death and remains far from the Sustainable Development Goal target. Whether health financing and macroeconomic instability are associated with newborn survival has rarely been examined for neonatal mortality specifically. Methods. We conducted an ecological time-series analysis of national annual data, covering 1990-2024 for macroeconomic models (n = 35) and 2000-2023 for health-financing models (n = 24), the periods for which published data exist; no values were imputed. Neonatal mortality came from the UN Inter-agency Group for Child Mortality Estimation 2025 round with 90% uncertainty intervals, and other series from the World Development Indicators. The primary model regressed log neonatal mortality on government health expenditure per capita (purchasing power parity), out-of-pocket share and currency instability, with a linear trend, a post-break trend spline and Newey-West standard errors; first differences without trend terms were the main sensitivity analysis. The break was located by segmented regression; currency instability was tested under four constructions. Results. The decline broke around 2010, the trend moving from -0.74 to +0.14 deaths per 1,000 annually (F = 145.4, p < 0.001). The subsequent rise fell within estimation uncertainty (2012: 37.6, 90% interval 33.9-41.5; 2022: 39.3, 33.4-46.4), supporting stagnation rather than reversal; Demographic and Health Surveys concur, reporting 42 per 1,000 for the five years preceding the 1990 survey and 41 preceding the 2024 survey. Government health expenditure per capita was inversely associated with neonatal mortality (-0.040, 95% CI -0.051 to -0.029, p < 0.001; first differences -0.016, p = 0.033) and was the only expenditure measure surviving both specifications; share-of-GDP measures did not (p = 0.196 and 0.889) and correlated positively in raw terms. Currency instability showed no association under any construction (p = 0.65-0.83). Public expenditure per capita moved non-monotonically, peaking in 2005, falling by 2010 and recovering by 2023 to a level still below the 2005 peak. Conclusions. Neonatal mortality in Nigeria is ecologically associated with public health expenditure per capita, but not with commonly used share-based measures, nor with currency instability. Rising public spending accompanied stalled progress, directing attention toward how health resources are converted into services. Annual modelled mortality estimates could not support year-to-year inference, a limitation relevant to comparable studies