1. Clinical Epidemiology Unit, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand
2. Department of Nursing, Uttaradit Hospital, Uttaradit 53000, Thailand
3. Department of General Surgery, Nakhon Sawan General Hospital, Nakhon Sawan 60000, Thailand
4. Department of General Surgery, Uttaradit General Hospital, Uttaradit 53000, Thailand
5. Department of General Surgery, Lampang General Hospital, Lampang 52000, Thailand
6. Clinical Epidemiology Society, Chiang Mai 50200, Thailand