Text and Data Mining valid from 2019-09-03
Received: 12 March 2019
Accepted: 20 August 2019
First Online: 3 September 2019
Compliance with ethical standards
: The authors report no conflict of interest regarding this work.
: This study was approved by our institutional ethical review board and was in accordance with the ethical standards and with the 1964 Helsinki declaration and its later amendments.
: For this retrospective study formal consent is not required.