1. Department of Health Services Research, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
2. Health Services Research & Development Center, University of Tsukuba, Tsukuba, Japan
3. Department of General Internal Medicine, Eastern Chiba Medical Center, Togane, Japan
4. Health Services Center, Human Personnel Group, Sumitomo Heavy Industries, Ltd, Yokosuka, Japan
5. Faculty of Political Science and Economics, Waseda University, Tokyo, Japan