Text and Data Mining valid from 2018-12-12
Received: 27 September 2018
Revised: 4 November 2018
Accepted: 12 November 2018
First Online: 12 December 2018
Compliance with ethical standards
: The study has been approved by the appropriate ethics committee and has therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. All persons included into the study gave their informed consent prior to their inclusion in the study.