Public financing, external assistance and household health payments: a causal machine learning analysis of 173 countries, 2000–2023

Background Out-of-pocket (OOP) payments remain the dominant health financing mechanism in many countries while development assistance for health is contracting. Existing cross-country evidence on financing composition and household payments is weakened by an accounting identity linking regressors to the outcome and by the allocation of financing to high-burden settings. Methods We analyzed 4,141 country–year observations from 173 countries (2000–2023) using the WHO Global Health Expenditure Database and Sustainable Development Goal (SDG) indicators. Government and external shares of current health expenditure (CHE) were entered jointly, so each effect represents a reallocation from domestic private financing. The primary outcome was per capita real out-of-pocket spending. Double machine learning was applied across three specifications, culminating in a within-country design with three-year lags, pre-treatment covariates, and a baseline adjustment. Inference was country-cluster-robust. Results Within countries, reallocating 10 percentage points from private to government financing was associated with 11.4% lower out-of-pocket spending per capita (95% confidence interval [CI: 7.9–14.8]), and reallocating to external financing was associated with 14.7% lower spending (11.2–18.0); the difference was not significant ( p = 0.075). Conventional specifications overstated these effects by 2.6–2.9-fold. Share-based estimates matched the value implied by the accounting identity. Results were robust across all sensitivity analyses. No effects on tuberculosis, Human Immunodeficiency Virus (HIV), or maternal mortality were detected, and regional estimates did not support a policy typology. Conclusion Shifting financing toward pooled government or external sources is associated with lower household payments, but by far less than cross-country estimates suggest. Financing targets and assessments of aid withdrawal should rely on evidence from within the country.