Levels of evidence
| Level . | Type of evidence . |
|---|---|
| Ia | Evidence obtained from meta-analysis of randomized controlled trials |
| Ib | Evidence obtained from at least 1 randomized controlled trial |
| IIa | Evidence obtained from at least 1 well-designed controlled study without randomization |
| IIb | Evidence obtained from at least 1 other type of well-designed quasi-experimental study |
| III | Evidence obtained from well-designed nonexperimental 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 |
| Level . | Type of evidence . |
|---|---|
| Ia | Evidence obtained from meta-analysis of randomized controlled trials |
| Ib | Evidence obtained from at least 1 randomized controlled trial |
| IIa | Evidence obtained from at least 1 well-designed controlled study without randomization |
| IIb | Evidence obtained from at least 1 other type of well-designed quasi-experimental study |
| III | Evidence obtained from well-designed nonexperimental 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 |