Levels of evidence and grade of recommendations
| Level . | Type of evidence . |
|---|---|
| I | Evidence obtained from meta-analysis of multiple, well-designed, controlled studies. Randomized trials with low false-positive and low false-negative errors (high power). |
| II | Evidence obtained from at least one well-designed experimental study. Randomized trials with high false-positive and/or -negative errors (low power). |
| III | Evidence obtained from well-designed, quasi-experimental studies such as nonrandomized, controlled single-group, pre-post, cohort, time, or matched case-control series. |
| IV | Evidence from well-designed, nonexperimental studies such as comparative and correlational descriptive and case studies. |
| V | Evidence from case reports and clinical examples. |
| Level . | Type of evidence . |
|---|---|
| I | Evidence obtained from meta-analysis of multiple, well-designed, controlled studies. Randomized trials with low false-positive and low false-negative errors (high power). |
| II | Evidence obtained from at least one well-designed experimental study. Randomized trials with high false-positive and/or -negative errors (low power). |
| III | Evidence obtained from well-designed, quasi-experimental studies such as nonrandomized, controlled single-group, pre-post, cohort, time, or matched case-control series. |
| IV | Evidence from well-designed, nonexperimental studies such as comparative and correlational descriptive and case studies. |
| V | Evidence from case reports and clinical examples. |
| Grade . | Grade of recommendations . |
|---|---|
| A | There is evidence of type I or consistent findings from multiple studies of types II, III, or IV. |
| B | There is evidence of types II, III, or IV, and findings are generally consistent. |
| C | There is evidence of types II, III, or IV, but findings are inconsistent. |
| D | There is little or no systematic empirical evidence. |
| Grade . | Grade of recommendations . |
|---|---|
| A | There is evidence of type I or consistent findings from multiple studies of types II, III, or IV. |
| B | There is evidence of types II, III, or IV, and findings are generally consistent. |
| C | There is evidence of types II, III, or IV, but findings are inconsistent. |
| D | There is little or no systematic empirical evidence. |