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Funding This project was funded by the Center for Tobacco Products of the US Food and Drug Administration (FDA).
Disclaimer The findings and conclusions in this report are those of the authors and do not represent FDA or Centers for Disease Control and Prevention positions or policies.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Correction notice This paper has been amended since it was published Online First. Owing to a scripting error, some of the publisher names in the references were replaced with ’BMJ Publishing Group'. This only affected the full text version, not the PDF. We have since corrected these errors and the correct publishers have been inserted into the references.