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Contributors CH wrote the first draft and KRM provided edits and intellectual input. Both authors approved the final draft.
Competing interests CH and KRM are supported by the NIHR School for Primary Care Research Evidence Synthesis Working group (NIHR SPCR ESWG project 390). CH is also supported by the NIHR Oxford Biomedical Research Centre, is an NIHR Senior Investigator and Editor in Chief of BMJ Evidence-Based Medicine. KRM is an Associate Editor of BMJ EBM.
Patient consent for publication Not required.
Provenance and peer review Commissioned; internally peer reviewed.