Text and Data Mining valid from 2019-02-01
Received: 7 September 2018
Revised: 20 January 2019
Accepted: 22 January 2019
First Online: 1 February 2019
Compliance with ethical standards
: All authors declare that they have no conflict of interest.
: The study was approved by the institutional review board and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.