High | Based on consistent results from well-performed randomised controlled trials | Further research is very unlikely to change the estimate of the effect |
Moderate | Based on randomised controlled trials where there is evidence of bias or from other well-conducted study types (eg, well-executed observational studies) | Further research is likely to have an impact on the estimate of the effect |
Low | Based on observational evidence or from controlled trials with several serious limitations | Further research is likely to have an important impact |
Very low | Based on case studies or expert opinion | Estimates of effect are far from certain and more research is needed |