Funding for this research was provided by:
Text and Data Mining valid from 2018-11-01
Received: 14 June 2018
Revised: 19 October 2018
Accepted: 22 October 2018
First Online: 1 November 2018
Compliance with ethical statements
: The authors declare that they have no conflict of interest.
: For this type of study, formal consent is not required. Informed consent was obtained from all individual participants for whom identifying information is included in this article. The ethical board of the University of Cologne declared no ethical concerns (No. 17-057).