US Agency for Health Care Policy and Research: level of evidence
Levels of evidence . | Level type of evidence . | Grades of recommendations . | Recommendation . |
|---|---|---|---|
| Ia | Evidence obtained from meta-analysis of randomized controlled trials. | A | Required: at least one randomized controlled trial as part of the body of literature of overall good quality and consistency addressing specific recommendations. |
| Ib | Evidence obtained from at least one randomized control study. | A | Required: at least one randomized controlled trial as part of the body of literature of overall good quality and consistency addressing specific recommendations. |
| IIa | Evidence obtained from at least one well-designed controlled study without randomization. | B | Required: availability of well-conducted clinical studies but not randomized clinical trials on the topic of recommendation. |
| IIb | Evidence obtained from at least one other kind of well-designed quasi-experimental study. | B | Required: availability of well-conducted clinical studies but not randomized clinical trials on the topic of recommendation. |
| III | Evidence obtained from well-designed, nonexperimental descriptive studies, such as comparative studies, correlation studies, and case-controlled studies. | B | Required: availability of well-conducted clinical studies but not randomized clinicaltrials on the topic of recommendation. |
| IV | Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. | C | Required: evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. Indicates absence of directly applicable clinical studies of good quality. |
Levels of evidence . | Level type of evidence . | Grades of recommendations . | Recommendation . |
|---|---|---|---|
| Ia | Evidence obtained from meta-analysis of randomized controlled trials. | A | Required: at least one randomized controlled trial as part of the body of literature of overall good quality and consistency addressing specific recommendations. |
| Ib | Evidence obtained from at least one randomized control study. | A | Required: at least one randomized controlled trial as part of the body of literature of overall good quality and consistency addressing specific recommendations. |
| IIa | Evidence obtained from at least one well-designed controlled study without randomization. | B | Required: availability of well-conducted clinical studies but not randomized clinical trials on the topic of recommendation. |
| IIb | Evidence obtained from at least one other kind of well-designed quasi-experimental study. | B | Required: availability of well-conducted clinical studies but not randomized clinical trials on the topic of recommendation. |
| III | Evidence obtained from well-designed, nonexperimental descriptive studies, such as comparative studies, correlation studies, and case-controlled studies. | B | Required: availability of well-conducted clinical studies but not randomized clinicaltrials on the topic of recommendation. |
| IV | Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. | C | Required: evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. Indicates absence of directly applicable clinical studies of good quality. |
The criteria are summarized from Johnson et al.22