Table 1.
Level of evidence | Grading criteria |
---|---|
1a | Systematic reviews of RCTs including meta-analysis. |
| |
1b | Individual RCT with narrow confidence interval. |
| |
1c | Case of series “all or nothing.” |
| |
2a | Systematic review of cohort studies. |
| |
2b | Individual cohort study and low quality RCT. |
| |
2c | Outcome research study. |
| |
3a | Systematic review of case control studies. |
| |
3b | Individual case control study. |
| |
4 | Case series, poor quality cohort, and case control studies. |
| |
5 | Expert's opinion. |
Adapted from levels of evidence of the Oxford Center for Evidence-Based Medicine [62].