Levels of Evidence
General
General
From the Centre for Evidence-Based Medicine, Oxford
| Therapy/Prevention/Etiology/Harm: |
| 1a: | Systematic reviews (with homogeneity ) of randomized controlled trials |
| 1a–: | Systematic review of randomized trials displaying worrisome heterogeneity |
| 1b: | Individual randomized controlled trials (with narrow confidence interval) |
| 1b–: | Individual randomized controlled trials (with a wide confidence interval) |
| 1c: | All or none randomized controlled trials |
| 2a: | Systematic reviews (with homogeneity) of cohort studies |
| 2a–: | Systematic reviews of cohort studies displaying worrisome heterogeneity |
| 2b: | Individual cohort study or low quality randomized controlled trials (<80% follow-up) |
| 2b–: | Individual cohort study or low quality randomized controlled trials (<80% follow-up / wide confidence interval) |
| 2c: | 'Outcomes' Research; ecological studies |
| 3a: | Systematic review (with homogeneity) of case-control studies |
| 3a–: | Systematic review of case-control studies with worrisome heterogeneity |
| 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 rule validated on a test set. |
| 1a–: | Systematic review of Level 1 diagnostic studies displaying worrisome heterogeneity |
| 1b: | Independent blind comparison of an appropriate spectrum of consecutive patients, all of whom have undergone both the diagnostic test and the reference standard; or a clinical decision rule not validated on a second set of patients |
| 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 |
| 2a–: | Systematic review of Level >2 diagnostic studies displaying worrisome heterogeneity |
| 2b: | Any of: 1)independent blind or objective comparison; 2)study performed in a set of non-consecutive patients, or confined to a narrow spectrum of study individuals (or both) all of whom have undergone both the diagnostic test and the reference standard; 3) a diagnostic clinical rule not validated in a test set. |
| 3a: | Systematic review (with homogeneity) of case-control studies |
| 3a–: | Systematic review of case-control studies displaying worrisome heterogeneity |
| 4: | Any of: 1)reference standard was unobjective, unblinded or not independent; 2) positive and negative tests were verified using separate reference standards; 3) study was performed in an inappropriate spectrum of patients. |
| 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 rule validated on a test set. |
| 1a–: | Systematic review of inception cohort studies displaying worrisome heterogeneity |
| 1b: | Individual inception cohort study with >80% follow-up; or a clinical rule not validated on a second set of patients |
| 1c: | All or none case-series |
| 2a: | Systematic review (with homogeneity) of either retrospective cohort studies or untreated control groups in RCTs. |
| 2a–: | Systematic review of either retrospective cohort studies or untreated control groups in RCTs displaying worrisome heterogeneity |
| 2b: | Retrospective cohort study or follow-up of untreated control patients in an RCT; or clinical rule not validated in a test set. |
| 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' |
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