1. Laboratory of Emergency Medical Services, Seoul National University Hospital Biomedical Research Institute, Seoul, Korea.
2. Department of Social & Preventive Medicine, Inha University School of Medicine, Incheon, Korea.
3. Department of Emergency Medicine, Seoul National University College of Medicine, Seoul, Korea.
4. Department of Epidemiology & Biostatistics, Texas A&M University, College Station, TX, USA.
5. Department of Preventive Medicine, Graduate School of Public Health, Seoul National University, Seoul, Korea.