Quality of evidence based on the grades of recommendation, assessment, development and evaluation working group
| Underlying methodology | Quality rating |
| Randomised trials; or double-upgraded observational studies | High |
| Downgraded randomised trials; or upgraded observational studies | Moderate |
| Double-downgraded randomised trials; or observational studies | Low |
| Triple-downgraded randomised trials; or downgraded observational studies; or case series/case reports | Very low |
Reproduced with permission from Schünemann et al58 (©The Cochrane Collaboration).