1. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA
2. Center for Genes, Environment, and Health, National Jewish Health, Denver, Colorado, USA
3. Department of Geology, Brigham Young University, Provo, Utah, USA
4. Department of Epidemiology, Colorado School of Public Health, Aurora, Colorado, USA
5. Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado Denver, Aurora, Colorado, USA
6. Denver Veterans Affairs Medical Center, Denver, Colorado, USA
7. Department of Statistical Sciences, University of Toronto, Toronto, Ontario, Canada
8. Department of Statistics, North Carolina State University, Raleigh, North Carolina, USA
9. Division of Biostatistics and Bioinformatics and Department of Immunology and Genomic Medicine, National Jewish Health, Denver, Colorado, USA