1. Division of Pulmonary, Allergy, and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, Alabama.
2. Division of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.
3. Division of Pulmonary and Sleep Medicine, University of Alabama at Birmingham, Birmingham, Alabama.
4. Mel and Enid Zuckerman College of Public Health and the Arizona Respiratory Center, University of Arizona, Tucson, Arizona.