1. Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, Iowa, USA
2. Department of Biostatistics, College of Public Health, University of Iowa, Iowa City, Iowa, USA
3. Department of Computer Science, University of Iowa, Iowa City, Iowa, USA
4. Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA