Funding for this research was provided by:
National Research Foundation of Korea (2016R1A4A1010796, 2018M3A7B4071235)
Text and Data Mining valid from 2019-03-04
Received: 2 November 2018
Accepted: 13 February 2019
First Online: 4 March 2019
Compliance with ethical standards
: The author(s) declare that they have no competing interests.