Footnotes

• Funding The study was funded by Health Research Council of New Zealand.

• Competing interests None.

• Ethics approval The study was approved by the Madrid and Lugo hospital ethics committees, The Regional Committees for Research Ethics in Eastern and Southern Norway, Multi-region Ethics Committee and the Lower South Ethics Committee of New Zealand, the Lewisham Hospital and Guy's and St Thomas' Hospitals local research ethics committees, The Oxford Research Ethics Committee.

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