1. Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Iowa, Iowa City, Iowa
2. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Albany Medical College, Albany, New York
3. Slone Epidemiology Center at Boston University, Boston, Massachusetts
4. Department of Pulmonary Medicine, Respiratory Institute, Cleveland Clinic, Cleveland, Ohio; and
5. Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of California, San Francisco, San Francisco, California