[1] Division of Pulmonary, Allergy and Critical Care Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA
[2] Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
[3] Leonard Davis Institute for Health Economics, University of Pennsylvania, Philadelphia, PA
[4] Division of Pulmonary and Critical Care Medicine, University of North Carolina, Chapel Hill, NC
[5] CRISMA Laboratory (Clinical Research, Investigation and Systems Modeling of Acute Illness), Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA
[6] ZD Associates, Perkasie, PA
[7] Division of Pulmonary and Critical Care, University of Michigan, Ann Arbor, MI