Text and Data Mining valid from 2018-03-30
Received: 3 December 2017
Accepted: 21 March 2018
First Online: 30 March 2018
Compliance with ethical standards
: Drs. Hitoshi Harada, Shingo Kanaji, Hiroshi Hasegawa, Masashi Yamamoto, Yoshiko Matsuda, Kimihiro Yamashita, Takeru Matsuda, Taro Oshikiri, Yasuo Sumi, Tetsu Nakamura, Satoshi Suzuki, and Yoshihiro Kakeji have no conflicts of interest or financial ties to disclose.