Text and Data Mining valid from 2019-07-22
Received: 2 January 2019
Accepted: 15 July 2019
First Online: 22 July 2019
Ethics approval and consent to participate
: This study has been approved by ethics committee of the medical faculty of the University Duisburg-Essen (05-2803).
: Not applicable.
: The authors declare that they have no competing interests.