Levels of Evidence
Select an evidence rating scale to display detailed information.
- Centre for Evidence-Based Medicine, Oxford (1a-5)
- SORT: Strength-of-Recommendation Taxonomy (A,B,C)
- GRADE: Grading of Recommendations Assessment, Development and Evaluation (A,B,C,D)
- Practice Guidelines rating scales (various)
From the Centre for Evidence-Based Medicine, Oxford
For the most up-to-date levels of evidence, see www.cebm.net/?o=1025
Therapy/Prevention/Etiology/Harm:
| 1a: | Systematic reviews (with homogeneity) of randomized controlled trials |
|---|---|
| 1b: | Individual randomized controlled trials (with narrow confidence interval) |
| 1c: | All or none randomized controlled trials |
| 2a: | Systematic reviews (with homogeneity) of cohort studies |
| 2b: | Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up) |
| 2c: | "Outcomes" Research; ecological studies |
| 3a: | Systematic review (with homogeneity) of case-control studies |
| 3b: | Individual case-control study |
| 4: | Case-series (and poor quality cohort and case-control studies) |
| 5: | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" |
Diagnosis:
| 1a: | Systematic review (with homogeneity) of Level 1 diagnostic studies; or a clinical decision rule with 1b studies from different clinical centers. |
|---|---|
| 1b: | Validating cohort study with good reference standards; or clinical decision rule tested within one clinical center |
| 1c: | Absolute SpPins And SnNouts (An Absolute SpPin is a diagnostic finding whose Specificity is so high that a Positive result rules-in the diagnosis. An Absolute SnNout is a diagnostic finding whose Sensitivity is so high that a Negative result rules-out the diagnosis). |
| 2a: | Systematic review (with homogeneity) of Level >2 diagnostic studies |
| 2b: | Exploratory cohort study with good reference standards; clinical decision rule after derivation, or validated only on split-sample or databases |
| 3a: | Systematic review (with homogeneity) of 3b and better studies |
| 3b: | Non-consecutive study; or without consistently applied reference standards |
| 4: | Case-control study, poor or non-independent reference standard |
| 5: | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" |
Prognosis:
| 1a: | Systematic review (with homogeneity) of inception cohort studies; or a clinical decision rule validated in different populations. |
|---|---|
| 1b: | Individual inception cohort study with > 80% follow-up; or a clinical decision rule validated on a single population |
| 1c: | All or none case-series |
| 2a: | Systematic review (with homogeneity) of either retrospective cohort studies or untreated control groups in randomized controlled trials. |
| 2b: | Retrospective cohort study or follow-up of untreated control patients in a randomized controlled trial; or derivation of a clinical decision rule or validated on split-sample only |
| 2c: | "Outcomes" research |
| 4: | Case-series (and poor quality prognostic cohort studies) |
| 5: | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" |
Note: A minus sign "-" may be added to denote evidence that fails to provide a conclusive answer because it is either (a) a single result with a wide Confidence Interval; OR (b) a Systematic Review with troublesome heterogeneity. Such evidence is inconclusive, and therefore can only generate Grade D recommendations.
