Grades used when assessing the full body of evidence contributing to a statement
| A | Consistent level 1 studies |
| B | Consistent level 2 or 3 studies, or extrapolations of level 1 studies |
| C | Level 4 studies, or extrapolations of level 2 or 3 studies |
| D | Level 5 studies or inconsistent studies of other levels |
Information from [2].