Categories of evidence185
| Level | Type of evidence |
|---|---|
| Ia | Evidence obtained from meta-analysis of randomised controlled trials |
| Ib | Evidence obtained from at least one randomised controlled trial |
| IIa | Evidence obtained from at least one well designed controlled study without randomisation |
| IIb | Evidence obtained from at least one other type of well designed quasi-experimental study |
| III | Evidence obtained from well designed non-experimental descriptive studies such as comparative studies, correlation studies, and case controlled studies |
| IV | Evidence obtained from expert committee reports and/or clinical experiences of respected authorities |