Text and Data Mining valid from 2019-01-07
Received: 4 September 2018
Accepted: 17 December 2018
First Online: 7 January 2019
Ethics approval and consent to participate
: All procedures performed in studies involving human participants 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. As a retrospective study in Germany, a separate approval is waived.
: Not applicable.
: The authors declare that they have no competing interests.
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