On the first day of each semester, I ask my students to state the important factors accounting for improved population health. Eventually someone says, "Nutrition!" Others rapidly follow with "sanitary sewage disposal," "clean water," "better education," and "increased incomes!" When asked to list medical advances improving population health, there are many false starts until "asepsis," "improved surgical technique," "anesthesia," "antibiotics," "vaccines," "prescription pharmaceuticals," "fluoride," and the like. David Kindig reminds us of the importance of population health and how little we know of the health effects of modern medicine, in the tradition of Sigismund Peller, Thomas McKeown, and A. L. Cochrane.