Footnotes

• Contributors The authors undertook all research for this article and had access to all data. IAS conceived the idea for the article and wrote the first draft; LCG, JHM, PIP and CAM critically reviewed the manuscript, suggested amendments and provided additional references.

• Competing interests All authors except IAS declared that the answer to the questions on the competing interest form are all NO and therefore have nothing to declare. IAS has declared he was a recipient of a grant from the Princess Alexandra Hospital Private Practice Research Fund.

• Guarantor IAS as the principal investigator had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.