Table 1 Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence [17]
Level | Criteria |
Level 1 | Systematic review of randomized trials or n-of-1 trials |
Level 2 | Randomized trial or observational study with dramatic effect including crossover studies |
Level 3 | Non-randomized controlled cohort/follow-up study |
Level 4 | Case-series, case–control, or historically controlled studies |
Level 5 | Mechanism-based reasoning |