Funding for this research was provided by:
Bundesministerium für Bildung und Forschung (01EL1422B)
Received: 23 July 2018
Accepted: 15 October 2018
First Online: 23 October 2018
Ethics approval and consent to participate
: The study protocol was approved by the Ethics Committee of the University Bremen on April 17, 2018. All participants receive written and oral information about the study and give written informed consent for study participation and use of their data.
: Not applicable.
: The authors declare that they have no competing interests.
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