Level of evidence
| Category | Evidence from: |
|---|---|
| Ia | Meta-analysis of RCTs |
| 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 respected authorities, or both |