Evidence hierarchy
| Category of evidence | Type of study |
|---|---|
| Ia | Meta-analyses of RCT or RCT ≥1 result |
| Ib | RCT |
| IIa | Controlled study without randomisation |
| IIb | Quasi-experimental study |
| III | Non-experimental descriptive studies such as comparative, correlation and case–control studies |
| IV | Expert committee reports or opinion or clinical experience of respective authorities, or both |
Modified from Shekelle et al.5
RCT, randomised controlled trial.