Received: 12 October 2018
Accepted: 26 April 2019
First Online: 17 May 2019
Ethics approval and consent to participate
: The institutional review boards approved the study. The school authorities (headteachers and teachers) were informed about the research project and its goals, and discussed and approved the online questionnaire. The school authorities informed parents of minors about the study and obtained their consent.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.