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Contributors DC wrote the first draft and KR contributed in the revision of the draft.
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.
Competing interests DC and KR have received support from the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre, British Heart Foundation and the Oxford Martin School. The views expressed are those of the authors and not necessarily those of the National Health Service, the NIHR or the Department of Health and Social Care.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.
Provenance and peer review Commissioned; internally peer reviewed.
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