Text and Data Mining valid from 2019-01-11
Received: 7 June 2017
Accepted: 19 December 2018
First Online: 11 January 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: All procedures performed in studies involving retrospective anonym data of human beings 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.