Text and Data Mining valid from 2018-05-21
Received: 10 June 2017
Revised: 8 May 2018
Accepted: 10 May 2018
First Online: 21 May 2018
Compliance with ethical standards
: The authors declare that they have no financial conflicts of interest regarding this study.
: The ethical committee of the Canton of Zurich waived our study since they decided that it did not need formal approval according to the regulations of the law on human research in Switzerland (KEK-ZH 2014-0400).
: Informed consent was not deemed since the data were fully anonymous.