1. Department of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada
2. Department of Medicine and Center for Sleep and Circadian Neurobiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
3. Department of Medicine, Corporal Michael J. Crescenz VA Medical Center, Philadelphia, Pennsylvania
4. Sleep Medicine and Research Center, St. Luke's Hospital, Chesterfield, Missouri
5. Department of Psychiatry, Stanford University, Palo Alto, California
6. Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland