Accounting for aid: estimating the impact of United States' global health investments on mortality among women of reproductive age using synthetic control and Bayesian methods.

Background: The United States government (USG) is a key global actor in preventing mortality and supporting lifesaving health services among women and children in low- and middle-income countries (LMICs). Since the Foreign Assistance Act of 1961, USG has funded global health programmes targeting specific conditions and strengthening health systems for the delivery of essential services via the United States Agency for International Development (USAID) and other USG agencies. However, directly quantifying and attributing the impact of USG health investments is challenging due to the inability of conducting randomised control trials for such large programmes at scale. In this study, we compared two quasi-experimental impact evaluation approaches to estimate the effects of sustained USG health investments on mortality among women of reproductive age (WRA). Methods: We employed synthetic control analysis and a Bayesian alternative to synthetic control to estimate the impact of USG's global health investments on WRA mortality rate across 16 LMICs that received sustained, multifaceted, and above-average USAID global health funding levels from 2005 to 2019. Results: Countries receiving sustained, multifaceted, and above-average USAID global health funding had a reduction in the annual WRA mortality rate by 0.65 deaths per 1000 WRA throughout the post-treatment period. For the years (i.e. 2009-2019) where the effect estimates are statistically significant (P < 0.001), the reduction in WRA mortality rate was 0.80 deaths per 1000 WRA. Sensitivity analyses and Bayesian modelling supported the robustness of these findings. We conservatively estimated that about 1.0-1.3 million WRA deaths were averted in study countries between 2009 and 2019 as a result of USG health investments. Conclusions: Our results suggest that well-funded donor initiatives can substantially reduce WRA mortality rates beyond what would have been achieved without such investments. Sustained donor investments significantly reduce WRA mortality, underscoring the transformative potential of well-funded global health initiatives. Our study also demonstrates that synthetic control and Bayesian models are valuable tools for evaluating the impact of large-scale global health financing.