Received: 25 February 2020
Accepted: 28 May 2020
First Online: 25 June 2020
Ethics approval and consent to participate
: The study protocol was approved by the ethics committee of Saarland University (no. 16–2). All respondents gave written informed consent before they participated in the study in accordance with the Declaration of Helsinki .
: Not applicable.
: The authors declare that they have no competing interests.