1. Division of Pulmonary, Allergy, and Critical Care, Department of Medicine,
2. Department of Surgery, and
3. Division of Pulmonary, Allergy, and Critical Care, Department of Medicine, Columbia University, New York, New York;
4. Division of Pulmonary Medicine, Department of Medicine, Duke University, Durham, North Carolina;
5. Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of California, San Francisco, San Francisco, California; and
6. Department of Biostatistics, Epidemiology, and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania;
7. Department of Mathematics, West Chester University, West Chester, Pennsylvania