Text and Data Mining valid from 2019-05-02
Received: 14 February 2019
Accepted: 16 April 2019
First Online: 2 May 2019
Ethics approval and consent to participate
: This is a retrospective study using anonymized data. Due to the design of the study the need for ethic approval was waived.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.