Text and Data Mining valid from 2019-02-11
Received: 8 November 2017
Accepted: 1 February 2019
First Online: 11 February 2019
Ethics approval and consent to participate
: Ethics approval was obtained from the Ethics Committee of the University of Hokkaido (reference number 17–75). The participant consent was verbal. We received ethics committee approval for verbal consent. All participants were informed of the purpose of the study. They were entirely voluntary and were assured that the data would be treated with confidentiality and anonymity.
: Not applicable.
: The authors declare that they have no competing interests.
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