Levels of quality of a body of evidence in the GRADE statement
| 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 |