Text and Data Mining valid from 2019-01-23
Received: 1 July 2018
Revised: 23 October 2018
Accepted: 22 November 2018
First Online: 23 January 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This study was approved by the Institutional Review Board of Keio University. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
: Informed consent was obtained from all individual participants included in the study.