Why do some countries rapidly adopt policies suggested by scientific consensus while others are slow to do so? Through a mixed methods study, we show that the institutional political economy of countries is a stronger and more robust predictor of health policy adoption than either disease burden or national wealth. Our findings challenge expectations in scholarship and among many international actors that policy divergence is best addressed through greater evidence and dissemination channels. Our study of HIV treatment policies shows that factors such as the formal structures of government and the degree of racial and ethnic stratification in society predict the speed with which new medical science is translated into policy, while level of democracy does not. This provides important new insights about the drivers of policy transfer and diffusion and suggests new paths for practical efforts to secure adoption of “evidence-based” policies
