Text and Data Mining valid from 2018-06-18
Received: 9 April 2018
Accepted: 21 May 2018
First Online: 18 June 2018
Change Date: 21 June 2018
Change Type: Correction
Change Details: In the version of this Brief Communication originally published, the two instances of ‘natural-to-high’ in the sixth and seventh paragraphs were incorrect; they should have read ‘naturally high’.
: The authors declare no competing interests.