Table 5.
Evidence levels and degrees of recommendation for therapies.
| Levels of evidence | |
| Level | Meaning |
| 1 | One or more randomized controlled clinical trials of sufficient sample size with a narrow confidence intervalMeta-analysis of randomized controlled clinical trials |
| 2 | Good quality cohort studyLow-quality randomized clinical trial (small sample size and >20% lost to follow-up) |
| 3 | Case-control studiesMeta-analysis of case-control studies |
| 4 | Case seriesLow-quality cohort studiesLow-quality case-control studies |
| 5 | Based on expert opinions, experimental studies or physiology |
| Grade/Strength of recommendation | |
| Grade | Meaning |
| A | Corresponding to level of evidence 1 |
| B | Corresponding to level of evidence 2 or 3Extrapolated from level 1 studies involving populations other than the current population |
| C | Corresponding to level of evidence 4Extrapolated from level 2 or 3 studies involving populations other than the current population |
| D | Corresponding to level of evidence 5 |
Adapted from: Levels of evidence and grades of recommendation, Oxford Center for Evidence-Based Medicine, May 2001.