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Article History

Received: 19 December 2018

Accepted: 27 September 2019

First Online: 21 October 2019

Ethics approval and consent to participate

: “All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.” Active written parental consent was requested and obtained for all German and Italian participants, while passive written parental consent was obtained for all in other cities. Passive parental consent procedures were approved by local or national Ethical Committees (see list below). All adolescents agreed to participate via written consent. References of national Ethical Committee: Belgium: REF 2012/09OCT/461 N° enregistrement belge B403201215182 – Comité d’éthique Hospitalo-Facultaire des Cliniques Universitaires Saint-Luc; Germany: Ethical approval MLU Halle-Wittenberg: 2016-90 hm-bü; Supervisory school authority Han(n)over: H 1 R b - 81402 - 55 – 2016; Supervisory school authority Lüneburg (Celle): LG 1 R.22 – 503000; Portugal: General Directorate for education, approval number 0338600002 on the 26th of July 2016; The Netherlands: Medical Research Involving Human Subjects Act (WMO): reference number W16_252 # 16.297, 11 August 2016; Ireland: Research Ethics Committee – Dublin Institute of Technology: Ethical Clearance Ref 15-105, 16th June 2016; Finland: Ethics Committee of the Tampere Region, Statement 29/2016; Italy: Ethical Committee “Lazio 2”, protocol number 0068451/2016.

: Not applicable.

: The authors declare that they have no competing interests.