Limitations
A source of bias (performance bias and detection bias) in this randomised trial is the lack of blinding of survey participants and lead researcher. However, it was necessary to provide instructions to participants on how to complete the survey and for the lead researcher to access the survey database to extract data for analyses, monitor participation and provide updated reports and other tasks. A further limitation was that the sample size was guided by the need to include stakeholders to develop the overall COS rather than the trial itself.Data are missing from the analysis of the feedback effect, iteration effect and initial condition effect. These data relate to the five outcomes participants suggested in the survey. These outcomes were not rated and/or re-rated by all participants, so the rating trends for these outcomes were omitted from the analysis.Our analysis did not consider contextual differences between outcomes, assuming that the underlying mechanism influencing all outcomes was homogenous and, therefore could be omitted from the analysis (i.e. we did not include an ‘outcome’ term or interaction effects by the outcome in the analyses). Whilst this is a relatively strong assumption, it follows the analysis approach used by Gnatzy et al. [In terms of the COS itself, we do not know what the implications in the final COS would be if we had just run one survey approach. However, by conserving all outcomes rated as ‘undetermined’, we ensured that important outcomes were not removed and that they could be discussed further at the consensus meetings. We began with a large menu of potential outcomes, and neither Delphi method alone weaned the list down to a manageable number of outcomes to propose in a COS.