1. Department of Environmental, Agricultural and Occupational Health, College of Public Health, University of Nebraska Medical Center, Omaha, NE, USA
2. Department of Epidemiology, College of Public Health, University of Nebraska Medical Center, Omaha, NE, USA
3. Department of Biostatistics, College of Public Health, University of Nebraska Medical Center, Omaha, NE, USA
4. School of Community Health Sciences, University of Nevada, Reno, Nevada, USA