Text and Data Mining valid from 2019-02-26
Received: 18 December 2018
Revised: 10 February 2019
Accepted: 12 February 2019
First Online: 26 February 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants or animals performed by any of the authors.
: This study was approved by the medical ethics committee of each participating center; the requirement for informed consent was waived.