1. Harvard Business School, Boston, MA 02163, USA.
2. Ariadne Labs at Brigham and Women's Hospital and the Harvard T. H. Chan School of Public Health, Boston, MA 02215, USA.
3. Dana-Farber Cancer Institute, Boston, MA 02215, USA.
4. Harvard Program in Therapeutic Science, Harvard Medical School, Boston, MA 02115, USA.
5. Harvard Kennedy School, Cambridge, MA 02138, USA.
6. National Bureau of Economic Research, Cambridge, MA 02138, USA.