Evidence-Based Medicine criteria
| Level | Description |
|---|---|
| Adapted from the Oxford Centre for Evidence-Based Medicine criteria.8 | |
| 1a | Systematic review of randomised controlled trials |
| 1b | Randomised controlled trial |
| 2 | Cohort study (consecutive patients) or low quality randomised controlled trial (for example, <80% follow up) |
| 3 | Open label, non-randomised study with historical or other control group or open label study using convenience (that is, non-consecutive) or unspecified sample; cohort studies with five or fewer patients |
| 4 | Case series (that is, not designed as a clinical study; typically including five or fewer patients) |