1. a Department of Environmental and Radiological Health Sciences , Colorado State University , Ft. Collins, Colo, USA
2. b Department of Public Health and Health Care , Yerevan State Medical University , Yerevan, Armenia
3. c Institute for Rural and Environmental Health, Department of Occupational and Environmental Health, The College of Public Health , The University of Iowa , Iowa City, Iowa
4. d Department of Biostatistics , The College of Public Health, The University of Iowa , Iowa City, Iowa