Text and Data Mining valid from 2019-10-29
Received: 10 July 2019
Accepted: 17 October 2019
First Online: 29 October 2019
Ethics approval and consent to participate
: The study was approved by the Institutional Review Board in Gunma University. Appropriate consents, permissions and releases were obtained.
: Not applicable.
: The authors declare that they have no competing interests.