Article History
Received: 31 August 2018
Revised: 27 December 2018
Accepted: 7 January 2019
First Online: 15 January 2019
Compliance with ethical standards
: This cross-sectional study was approved by the ethics committee of the Medical Faculty of the Heinrich-Heine University Düsseldorf, Germany.
: The authors declare that they have no conflict of interest.
: 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 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.
: Informed consent was obtained from all individual participants in the study.