1. Department of Epidemiology and Biostatistics, College of Public Health and Health Informatics; King Saud bin Abdulaziz University for Health Sciences; Riyadh Saudi Arabia
2. Department of Mathematics and Statistics; Air Force Institute of Technology; 2950 Hobson Way, WPAFB OH 45433 U.S.A.
3. Department of Biostatistics, School of Medicine, Box 980032; Virginia Commonwealth University; Richmond VA 23298 U.S.A.