Text and Data Mining valid from 2018-12-11
First Online: 11 December 2018
Compliance with ethical standards
: 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 retrospective study was approved by the institutional review board and informed consent was waived.