How can a marathon be dangerous even if you don’t run the race? Does your doctor follow medical advice any better than you do? Just how dangerous was it to go to a birthday party at the height of the pandemic? These are the kinds of questions that intrigue Dr. Bapu Jena, a rare double threat — he’s both an M.D. and a Ph.D. economist at Harvard. Each week on Freakonomics, M.D., Jena digs into fascinating research to discover the hidden side of healthcare.