Funding for this research was provided by:
Japan Society for the Promotion of Science (JP26590267, JP15H03516)
Received: 30 October 2018
Accepted: 25 October 2019
First Online: 13 November 2019
Ethics approval and consent to participate
: All performed procedures were in accordance with the ethical standards and approved by the institutional research committees of the first (17002) and the third author (A2016-035). The principals of the two elementary schools agreed to participate in the study. Only the data that were obtained through an opt-out consent process from the students’ parents were analyzed.
: Not applicable.
: The authors declare that they have no competing interests.