1. Department of General Medicine and Primary Care, University of Tsukuba Hospital, Tsukuba, Japan.
2. Kamisu Clinical Education and Training Center, Faculty of Medicine, University of Tsukuba, Kamisu, Japan.
3. Primary Care and Medical Education, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.
4. Department of Biostatistics, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.