1. Palliative and Advanced Illness Research Center, University of Pennsylvania, Philadelphia
2. Division of Pulmonary, Allergy, and Critical Care, Department of Medicine, University of Pennsylvania, Philadelphia
3. Department of Medical Ethics and Health Policy, University of Pennsylvania, Philadelphia
4. Corporal Michael J. Crescenz VA Medical Center, Philadelphia, Pennsylvania
5. Tulane University School of Medicine, New Orleans, Louisiana
6. Department of Biostatistics, Vanderbilt University, Nashville, Tennessee
7. Department of Biostatistics, Epidemiology and Informatics, University of Pennsylvania, Philadelphia