Text and Data Mining valid from 2019-02-04
Received: 4 March 2018
Accepted: 24 December 2018
First Online: 4 February 2019
<!--Emphasis Type='Bold' removed-->Compliance with ethical standards
: Zheng Bobo, Wang Xin, Li Jiang, Wang Quan, Bi Liang, Deng Xiangbing and Wang Ziqiang have no conflicts of interest or financial ties to disclose.