Evidence hierarchy (modified from Shekelle et al11)
| Category of evidence | Type of study |
|---|---|
| RCT, randomised controlled trial. | |
| Ia | Meta-analysis of RCTs or >1 RCT with similar results |
| 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 |