1
Department of Biostatistics and Demography, 2
Department of Epidemiology, Faculty of Public Health, 4
Cancer Unit, 5
Department
of Pediatrics, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand, 3
Clinical Trial Service Unit and Epidemiological
Studies Unit, University of Oxford, Oxford, United Kingdom *For correspondence: supannee@kku.ac.th