Summary of The Oxford Levels of Evidence 2
| Level 1 | Level 2 | Level 3 | Level 4 | Level 5 |
| Systematic review or meta-analysis | Randomized trial or observational study with dramatic effect | Non-randomized controlled cohort or follow-up study | Case series, case–control or historically controlled study | Mechanism-based reasoning |
Adapted from OCEBM (Oxford Center for Evidence-Based Medicine) Levels of Evidence Working Group, “The Oxford Levels of Evidence 2.”26