Funding for this research was provided by:
Ministry of Health, Labour and Welfare (19AA2007, H30-Policy-Designated-004)
Ministry of Education, Culture, Sports, Science and Technology (17H04141)
Text and Data Mining valid from 2019-11-06
Received: 16 July 2019
Accepted: 20 September 2019
First Online: 6 November 2019
Ethics approval and consent to participate
: The study was approved by the Institutional Review Board of the University of Tokyo. The board waived the need for informed consent, as this was a retrospective study.
: The Institutional Review Board waived the requirement for informed consent because of the anonymous nature of the data.
: The authors declare that they have no competing interests.