1. Palliative Care Center and Department of Family Medicine, Korea University Guro Hospital, Seoul, South Korea
2. Department of Family Medicine, Gil Medical Center, Gachon University College of Medicine, Incheon, South Korea
3. Department of Statistics, Dongguk University, Seoul, South Korea
4. Palliative Care Center, Korea University Guro Hospital, Seoul, South Korea
5. Department of Medicine, Korea University College of Medicine, Seoul, South Korea