Funding for this research was provided by:
Received: 7 June 2017
Accepted: 24 August 2017
First Online: 2 September 2017
Ethics approval and consent to participate
: The study was approved by the University of Freiburg Ethics Committee (EK 358/15) and informed consent was waived.
: Not applicable.
: The authors declare that they have no competing interests.
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