A Quantitative Theory of the HIV Epidemic

The paper presented in this Research Seminar develops a novel empirical approach to identify the effectiveness of policies against a pandemic. The essence of the author's approach is the insight that epidemic dynamics are best tracked over stages, rather than over time. They use a normalization procedure that makes the pre-policy paths of the epidemic identical across regions. The procedure uncovers regional variation in the stage of the epidemic at the time of policy implementation. This variation delivers clean identification of the policy effect based on the epidemic path of a leading region that serves as a counterfactual for other regions. The authors apply their method to evaluate the effectiveness of the nationwide stay-home policy enacted in Spain against the Covid-19 pandemic. They find that the policy saved 15.9% of lives relative to the number of deaths that would have occurred had it not been for the policy intervention. Its effectiveness evolves with the epidemic and is larger when implemented at earlier stages.