Revised SIGN grading system: grades of recommendation
| A | At least one meta-analysis, systematic review, or RCT rated as 1++ and directly applicable to the target population; or |
| A systematic review of RCTs or a body of evidence consisting principally of studies rated as 1+ directly applicable to the target population and demonstrating overall consistency of results. | |
| B | A body of evidence including studies rated as 2++ directly applicable to the target population and demonstrating overall consistency of results; or |
| Extrapolated evidence from studies rated as 1++ or 1+. | |
| C | A body of evidence including studies rated as 2+ directly applicable to the target population and demonstrating overall consistency of results; or |
| Extrapolated evidence from studies rated as 2+. | |
| D | Evidence level 3 or 4; or |
| Extrapolated evidence from studies rated as 2+. |