Table 1.
Oxford Centre for Evidence-based Medicine – Levels of evidence and recommendation
| Level of evidence | |
|---|---|
| 1A | Systematic review (SR) of Randomized controlled trial (RCT) |
| 1B | Individual RCT |
| 1C | All-or-none |
| 2A | SR of cohort studies |
| 2B | Individual cohort study |
| 2C | “Outcomes” Research; Ecological studies |
| 3A | SR of case-control studies |
| 3B | Individual Case-Control Study |
| 4 | Case-series |
| 5 | Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles” |
| Recommendations | |
| A | Consistent level 1 studies |
| B | Consistent level 2 or 3 studies or extrapolations from level 1 studies |
| C | Level 4 studies or extrapolations from level 2 or 3 studies |
| D | Level 5 evidence or troublingly inconsistent or inconclusive studies of any level |
From Centre for Evidence-Based Medicine in Oxford in the UK. http://www.cebm.net/oxford-centre-evidence-based-medicine-levels-evidence-march-2009/