4.2 Reporting standards of included COSs
For the COS-STAR checklist, only 34.1% of studies can identify in the title that the paper reports the development of a COS. The compliance rates of 8 criteria belonging to ”introduction” and ”discussion” sections were greater than 85%, and the compliance rates of 9 criteria in the methods section ranged from 27.3% - 68.2%. The influence of methodology on the quality of COSs was considered significant. More than a third of the studies did not fully report protocol/registry entry, information sources, and funding sources, which may reduce the transparency of the COS developed. Moreover, only a few studies published their protocol on peer-reviewed journals, and most registered with limited information. We could not find any registration information or published protocol for more than 40% of COSs. Given that no study met the item 11 criterion (describe any changes from the protocol), further consideration is needed whether COS not deviating from the protocol should report this item. This would improve the applicability and suitability of this criterion. The characteristics of the people involved were not presented in 61.4% of studies. All outcomes considered at the start of the consensus process and descriptions of any other outcomes introduced/dropped during the consensus process were absent in more than half of the studies. The recommended outcomes in 43.2% of COSs were unclear or ambiguous, which may limit their use. Only twenty-four (54.5%) COSs met all two other information criteria (sources of funding and conficts of Interest). Total COS-STAR compliance criteria of OG COSs was significantly positively correlated with prior protocol, indicating that COS developed with prior protocol may improve the reporting quality of COS reporting. Therefore, further studies should consider improving the transparency and robustness of the reporting standard through publishing a previous protocol based on Core Outcome Set-STAndardised Protocol Items (COS-STAP) statement.3