Funding for this research was provided by:
Ministry of Health, Labour and Welfare (H28-Kankaku-Ippan-001)
Text and Data Mining valid from 2019-06-28
Received: 16 January 2019
Accepted: 22 June 2019
First Online: 28 June 2019
Ethics approval and consent to participate
: Only guardians for whom written informed consent were obtained were included in the study, and the study was approved by the ethics committee of the University of Tokyo (IRB number: 11316).
: Not applicable.
: The authors declare that they have no competing interests.