Table 2.
Oxford centre for evidence-based medicine level of evidence.8
| Grade of Recommendation | Levels of Evidence | Type of Study |
|---|---|---|
| A | 1a | SR (with homogeneity) of RCTs and of prospective cohort studies |
| 1b | Individual RCT with narrow confidence interval, prospective cohort study with good follow-up | |
| 1c | All or none studies, all or none case series | |
| B | 2a | SR (with homogeneity) of cohort studies |
| 2b | Individual cohort study | |
| 2c | Outcomes research, ecological studies | |
| 3a | SR of case control studies, SR of 3b and better studies | |
| 3b | Individual case control study, nonconsecutive cohort study | |
| C | 4 | Case series/case report, poor quality cohort studies |
| D | 5 | Expert opinion, bench research |
SR, systematic reviews; RCTs, randomized control trials.