Funding for this research was provided by:
The Ministry of Education, Culture, Sports, Science and Technology, Japan (17H04141)
Ministry of Health, Labour and Welfare (H29-ICT-General-004 and H30-Policy-Designated-004)
Received: 4 July 2019
Accepted: 2 December 2019
First Online: 12 December 2019
Ethics approval and consent to participate
: The present study was approved by the University of Tokyo Institutional Review Board. Due to the anonymous nature of the database, the standard requirement for informed consent was waived for this study.
: Not applicable
: The authors declare that they have no competing interests.