Funding for this research was provided by:
Ministry of Health, Labour and Welfare (H29-Policy-Designated-009 and H29-ICT-General-004)
Article History
Received: 22 December 2017
Accepted: 4 June 2019
First Online: 18 June 2019
Ethics approval and consent to participate
: Written informed consent was not required because of the anonymous nature of the data. The need for written consent was formally waived by the ethics committee. The Institutional Review Board at The University of Tokyo approved the study. All authors obtained permission to use the national inpatient database.
: Not applicable.
: The authors declare that they have no competing interests.