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Article History

Received: 14 June 2018

Accepted: 10 April 2019

First Online: 3 May 2019

Compliance with ethical standards

:

: The authors declare that they have no conflict of interest.

: All procedures performed in this study were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study proposal was approved by the Ethics Committee of the University of Regensburg (10-101-0010, Feb 19, 2010).

: For this type of study, informed consent is not required.