Funding for this research was provided by:
Text and Data Mining valid from 2018-07-11
Received: 1 December 2017
Accepted: 5 July 2018
First Online: 11 July 2018
Compliance with ethical standards
: The research was performed in accordance with the ethical standard laid down in the 19964 Declaration of Helsinki and its later amendments.
: The authors declare that they have no conflict of interest.