Data extraction and quality assessment
Two authors independently screened all entries (KG and BD). Where protocols had been published, study characteristics, proposed methodology and consensus methods were recorded. The quality of published COS protocols was assessed using the COS-STAP.(13) Where authors had published systematic reviews, the study characteristics, methodology and results were collated. If a COS was published, study characteristics, methodology for potential core outcome identification, consensus methods used to determine final COS were collated. The methodological and reporting quality of the COS development process was assessed using the COS-STAD and the COS-STAR.(14, 15). A green rating was given when all criteria in the specific domain were achieved, red where they were not fulfilled and yellow if fulfilment was unclear. Emails were sent to registered authors if no publications could be found to identify potential grey literature, or if the milestones proposed by the authors during the COMET initiative registration process had passed.