1. Department of Medicine, Division of Sleep Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA
2. Department of Medicine, The Pulmonary Center, Boston University School of Medicine, Boston, MA
3. Veterans Affairs Boston Healthcare System, West Roxbury, MA
4. Department of Biostatistics, Johns Hopkins University
5. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD
6. Department of Medicine, Division of Sleep Medicine, Brigham and Women's Hospital and Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA