Footnotes

• Contributors PL designed the study. FJL undertook data collection. PL and FJL analysed the data and prepared the manuscript.

• Funding The study was partly funded by the National Institute for Health Research Newcastle Biomedical Research Centre based at Newcastle Hospitals Foundation Trust and Newcastle University, UK.

• Competing interests None.

• Ethics approval Newcastle University ethics committee.

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