Text and Data Mining valid from 2018-12-11
Received: 13 July 2018
Accepted: 6 December 2018
First Online: 11 December 2018
Compliance with Ethical Standards
: The authors declare that they have no competing interests.
: This study was approved by the ethical review board of the Canton Zurich, Switzerland, and was performed in full accordance with the Declaration of Helsinki (2015-0322).
: All parents provided written informed consent after study procedures and aims had been explained in detail. All children provided verbal assent, while adolescents older than 14 years of age also provided written informed consent.