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Article History

Received: 7 February 2017

Revised: 6 May 2017

Accepted: 12 May 2017

First Online: 12 June 2017

Compliance with ethical standards

:

: The scientific guarantor of this publication is Prof. Dr. Andreas G. Schreyer

: The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

: The authors state that this work has not received any funding.

: One of the authors has significant statistical expertise.

: Written informed consent was waived by the Institutional Review Board.

: Institutional Review Board approval was obtained as The Independent Ethics Committee at the Regensburg University confirmed that for this scientific project no ethical approval or commission’s opinion was necessary due to the fact that according to our applicable laws and guidelines such a retrospective study without any study-related clinical intervention or use of patients’ personal data does not have to be submitted to the ethics committee.

: No study subjects or cohorts have been previously reported.

: • retrospective• observational• performed at one institution