Levels of evidence19
| Level | Type of evidence (based on AHCPR 1992) |
|---|---|
| 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 quasiexperimental study |
| III | Evidence obtained from well designed non-experimental descriptive studies, such as comparative studies, correlation studies, and case-control studies |
| IV | Evidence obtained from expert committee reports or opinions and/or clinical experience of respected authorities |