1. Section for Clinical Epidemiology and Biostatistics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand
2. Department of Surgery, The University of Mississippi Medical Center, Jackson, MS 39216, USA
3. Centre for Clinical Epidemiology and Biostatistics, The University of Newcastle, Newcastle, NSW 2300, Australia
4. Department of Biostatistics, Faculty of Public Health, Mahidol University, Bangkok 10400, Thailand