Footnotes

• Handling editor Runjan Chetty.

• Contributors SSK, SKL and BFR: substantial contributions to the conception or design of the work, or the acquisition, analysis or interpretation of data. SSK, SKL and DSC: drafting the work or revising it critically for important intellectual content. SSK and DSC: final approval of the version published. All authors: agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

• 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.

• Disclaimer The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of Southern California Permanente Medical Group.

• Competing interests None declared.

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