Text and Data Mining valid from 2018-08-02
Received: 13 February 2018
Accepted: 11 July 2018
First Online: 2 August 2018
Ethics approval and consent to participate
: The study protocol followed the guidelines for Epidemiological Studies in accordance with the Declaaration of Helsinki and was reviewed by the institutional review board at Waseda University.
: Not applicable.
: The authors declare that they have no competing interests.
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