1. Department of Anesthesiology and Pain Medicine, Harborview Medical Center, University of Washington, Seattle, Washington.
2. Department of Biostatistics, University of Washington, Seattle, Washington.
3. Division of Pulmonary, Allergy, and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania.
4. Division of Medical Ethics and Health Policy, University of Pennsylvania, Philadelphia, Pennsylvania.
5. Department of Biostatistics, University of Florida, Gainesville, Florida.
6. Division of Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, Washington.