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Article History

Received: 5 November 2018

Accepted: 11 January 2019

First Online: 18 January 2019

Ethics approval and consent to participate

: <i>NinJa</i> database is managed, operated, and organized by National Hospital Organization (NHO) Sagamihara hospital. The <i>NinJa</i> study protocol was reviewed and approved by the Ethics Committee of NHO Sagamihara hospital (2014031816) as well as by the ethics committee of each participating institution (NHO Hokkaido Medical center, NHO Asahikawa Medical Center, NHO Awara Hospital, University of Toyama Hospital, NHO Minami-Okayama Medical Center, Kurashiki Medical Center, NHO Beppu Medical Center, NHO Fukuoka National Hospital, NHO Kyushu Medical Center, NHO Ureshino Medical Center, NHO Miyakonojo Medical Center, Kumamoto Shinto General Hospital, Japanese Red Cross Kagoshima Hospital, Northern Okinawa Medical Center, Japanese Red Cross Kumamoto Hospital, NHO Kochi National Hospital, NHO Osaka Minami Medical Center, NHO Himeji Medical Center, Kyoto University hospital, NHO Toneyama National Hospital, Hyogo College of Medicine Hospital, Amagasaki Medical COOP Hospital, NHO Nagoya Medical Center, NHO Morioka National Hospital, Tsugaru General Hospital, NHO Shimoshizu National Hospital, NHO Chiba-East National Hospital, NHO Tokyo Medical Center, Tokyo Metropolitan Tama Medical Center, Tokyo Metropolitan Bokuto General Hospital, The University of Tokyo Hospital, Tokyo Medical University hospital, Tokyo Medical and Dental University Medical Hospital, Wakaba Hospital, Saitama Medical University Hospital, Yokohama Rosai Hospital, NHO Yokohama Medical Center, Niigata Rheumatic Center, Marunouchi Hospital, Teikyo University Chiba Medical Center, University of Tsukuba Hospital, Ogawa Red Cross Hospital, Tokyo Medical University Hachioji Medical Center, Kitasato University Hospital, St. Luke’s International Hospital).

: Not applicable.

: The authors declare that they have no competing interests.

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