They included fixed effects for hospitals and surgeons: "To test whether our findings were affected by including both hospital and surgeon fixed effects in the

They included fixed effects for hospitals and surgeons: "To test whether our findings were affected by including both hospital and surgeon fixed effects in the same regression models." [1] Perhaps the link could be changed to the paper itself? [1] https://www.bmj.com/content/371/bmj.m4381 https://www.bmj.com/content/371/bmj.m4381