Text and Data Mining valid from 2018-02-07
Received: 21 September 2017
Accepted: 1 February 2018
First Online: 7 February 2018
Compliance with ethical standards
: Tetsuya Yoshizaki, Daisuke Obata, Yasuhiro Aoki, Norihiro Okamoto, Hiroki Hashimura, Chise Kano, Megumi Matsushita, Atsushi Kanamori, Kei Matsumoto, Masahiro Tsujimae, Kenji Momose, Takaaki Eguchi, Shunsuke Okuyama, Hiroshi Yamashita, Mikio Fujita, Akihiko Okada have no conflicts of interest or financial ties to disclose.