1. Department of Anesthesiology and Pain Medicine, Yonsei University College of Medicine, Seoul, Korea.
2. Biostatistics Collaboration Unit, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Anesthesiology and Pain Medicine, Chung-Ang University Hospital, Seoul, Korea.
4. Anesthesia and Pain Research Institute, Yonsei University College of Medicine, Seoul, Korea.