1 Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA 52242, USA.
2 Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA 52242, USA; Obesity Research and Education Initiative and Fraternal Order of Eagles Diabetes Research Center, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA. Electronic address: wei-bao@uiowa.edu.