Footnotes

• Contributors All authors conceptualised and designed the study; JD conducted statistical analyses and drafted the manuscript; CM, KE, JB and DR provided advice on data analysis and interpretation and critically reviewed the manuscript; all authors approved the final version.

• Funding The study was funded by SA Government.

• Competing interests None.

• Ethics approval Ethics approval was provided by the University of Adelaide Human Research Ethics Committee.

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