Footnotes

• Contributors All authors had carefully read the article by McCarthy et al and analyzed their methods and data. CL, PW and CN suggested comment points and drafted this manuscript. CL critically revised comment points and this manuscript and is the author responsible for this paper. PW and CN revised comment points and this paper. All authors had seen and approved the final manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.