1. Department of Medicine, University of Washington, Seattle, WA, USA
2. Department of Health Services Research and Development, Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA
3. Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena, CA, USA
4. Pulmonary and Critical Care Medicine Section, VA Boston Health Care System, Boston, MA, USA
5. Harvard Medical School, Boston, MA, USA
6. Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA