1. Department of Statistics, North Dakota State University, Fargo, ND, USA
2. Department of Public Health, North Dakota State University, Fargo, ND, USA
3. Department of Health, Nutrition, and Exercise Sciences, Fargo, ND, USA
4. Fargo VA Healthcare System, Fargo, ND, USA
5. San Francisco Coordinating Center, California Pacific Medical Center Research Institute, San Francisco, CA, USA
6. Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA