Innovation Diffusion and Physician Networks: Keyhole Surgery for Cancer in the English NHS

We examine the effect of a physician network on medical innovation using novel matched patient-physician-hospital panel data. The data include every relevant physician and all patients in the English NHS for 15 years and physicians' workplace histories for more than 20. The dynamic network arising from physician mobility between hospitals over time allows us to separate unobserved physician and hospital heterogeneity from the effect of the network. We build on standard peer-effects models by adding cumulative peer behaviour and allow for particularly influential physicians ('key players'), whose identities we estimate. We find positive effects of peer innovation take-up, number of peers, and proximity in the network to both pioneers of the innovation and key players. Counterfactual estimates suggest that early intervention targeting young, connected physicians with early take-up can significantly increase aggregate take-up."