Article History
Received: 31 May 2018
Accepted: 18 December 2018
First Online: 14 January 2019
Compliance with ethical guidelines
:
: A. Lau, J. Schwarz and O. Stoll declare that they have no competing interests.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1975 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.