Funding for this research was provided by:
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (406740-139309)
Received: 20 November 2017
Accepted: 23 March 2018
First Online: 20 April 2018
Ethics approval and consent to participate
: The study was declared exempt from ethics review by the Zurich Cantonal Ethics Board (KEK-StV-Nr. 23/13). Participants were informed about the study in a cover letter. Questionnaire return was considered to imply consent to participate.
: Not applicable.
: The authors declare that they have no competing interests.
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