1. Department of Epidemiology, University of Nebraska Medical Center, Omaha, NE, USA.
2. Kinesiology and Sport Sciences Department, University of Nebraska at Kearney, Kearney, NE, USA.
3. Department of Biostatistics, University of Nebraska Medical Center, Omaha, NE, USA.
4. Department of Health Promotion, University of Nebraska Medical Center, Omaha, NE, USA.