Received: 3 July 2019
Accepted: 4 November 2019
First Online: 18 December 2019
Ethics approval and consent to participate
: The research project was approved by a suitably constituted Ethics Committee of the University of Lübeck on 9 October 2017, reference number 17–267. All study participants gave informed consent. Consent to participate was obtained in written form.
: Not applicable.
: The authors declare that they have no competing interests.