Michels, G.
Hempel, D.
Pfister, R.
Janssens, U.
Article History
Received: 20 December 2017
Revised: 13 February 2018
Accepted: 7 March 2018
First Online: 9 April 2018
Compliance with ethical guidelines
:
: G. Michels, D. Hempel, R. Pfister and U. Janssens declare that they have no competing interests.
: This article does not contain any studies with human participants or animals performed by any of the authors. Informed consent was obtained from all persons included in the survey.