Funding for this research was provided by:
Ministry of Health, Labour and Welfare (150903-01 and 180902-01)
Received: 15 September 2019
Accepted: 11 December 2019
First Online: 8 January 2020
Ethics approval and consent to participate
: This study was conducted in accordance with the guidelines proposed in the Declaration of Helsinki. The Ethical Committee of the National Institute of Occupational Safety and Health, Japan reviewed and approved the study protocol (ID H2810). The aims and design of this study were explained to each participant before they gave their written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.