Levels of evidence and grade of recommendation
| Level | Strength of evidence (Adapted from Muir Gray36) | Grade | Grade of recommendation (Cook et al37) |
|---|---|---|---|
| I | Strong evidence from at least one systematic review of multiple well designed randomised controlled trials | A | Supported by level I evidence and therefore highly recommended. |
| II | Strong evidence from at least one properly designed randomised controlled trial of appropriate size. | B | Supported by level II evidence, and therefore recommended |
| III | Evidence from well designed trials without randomisation, single group pre-post, cohort, time series or matched case-control studies | C | Supported by level III, evidence. Several potential clinical actions might be considered appropriate. |
| IV | Evidence from well designed non-experimental studies from more than one centre or research group | D | Supported by level IV and V evidence. The consensus route would have to be adopted. |
| Va | Opinions of respected authorities | D | |
| Vb | Clinical evidence, descriptive studies or reports of expert committees | D |