1. Division of Clinical Epidemiology, Research Center for Medical Sciences, The Jikei University School of Medicine , 3-25-8 Nishishimbashi, Minato-ku, Tokyo, 105-8461 , Japan
2. Section of Clinical Epidemiology, Department of Community Medicine, Graduate School of Medicine, Kyoto University , 54 Kawahara-cho, Syogoin, Sakyo-ku, Kyoto, 606-8507 , Japan
3. Department of General Medicine, Okinawa Chubu Hospital , 281 Miyazato, Uruma City, Okinawa, 904-2293 , Japan