Text and Data Mining valid from 2018-09-14
Received: 10 July 2018
Accepted: 4 September 2018
First Online: 14 September 2018
Ethics approval and consent to participate
: The study protocol was approved by the ethics committee of the University of Cologne (Ref. no. 12-162).
: Not applicable.
: The authors declare that they have no competing interests.
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