Text and Data Mining valid from 2018-02-17
Received: 10 November 2017
Accepted: 13 February 2018
First Online: 17 February 2018
Compliance with ethical standards
: All data generated or analyzed during this study are included in this published article (and its supplementary information files).
: The authors report no conflict of interests.
: Ethical approval for this study was not needed.
: This study included only already published data.