1. Department of Epidemiology, Emory University Rollins School of Public Health, Atlanta, GA 30322, USA
2. Department of Medicine, Division of Pulmonary, Allergy & Critical Care Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
3. Vietnam Era Twin Registry, VA Epidemiologic Research & Information Center & Department of Epidemiology, University of Washington School of Public Health, Seattle, WA 98195, USA
4. Department of Biomedical Informatics, Emory University School of Medicine, Atlanta, GA 30322, USA