Level | Therapy/Prevention, Aetiology/Harm | Prognosis | Diagnosis | Differential diagnosis/symptom prevalence study | Economic and decision analyses |
---|---|---|---|---|---|
1a | SR (with homogeneity*) of RCTs | SR (with homogeneity*) of inception cohort studies; CDR†validated in different populations | SR (with homogeneity*) of Level 1 diagnostic studies; CDR†with 1b studies from different clinical centres | SR (with homogeneity*) of prospective cohort studies | SR (with homogeneity*) of Level 1 economic studies |
1b | Individual RCT (with narrow Confidence Interval‡) | Individual inception cohort study with > 80% follow-up; CDR†validated in a single population | Validating** cohort study with good†††reference standards; or CDR†tested within one clinical centre | Prospective cohort study with good follow-up**** | Analysis based on clinically sensible costs or alternatives; systematic review(s) of the evidence; and including multi-way sensitivity analyses |
1c | All or none§ | All or none case-series | Absolute SpPins and SnNouts††| All or none case-series | Absolute better-value or worse-value analyses ††††|
2a | SR (with homogeneity*) of cohort studies | SR (with homogeneity*) of either retrospective cohort studies or untreated control groups in RCTs | SR (with homogeneity*) of Level >2 diagnostic studies | SR (with homogeneity*) of 2b and better studies | SR (with homogeneity*) of Level >2 economic studies |
2b | Individual cohort study (including low quality RCT; e.g., <80% follow-up) | Retrospective cohort study or follow-up of untreated control patients in an RCT; Derivation of CDR†or validated on split-sample§§§ only | Exploratory** cohort study with good†††reference standards; CDR†after derivation, or validated only on split-sample§§§ or databases | Retrospective cohort study, or poor follow-up | Analysis based on clinically sensible costs or alternatives; limited review(s) of the evidence, or single studies; and including multi-way sensitivity analyses |
2c | "Outcomes" Research; Ecological studies | "Outcomes" Research | Â | Ecological studies | Audit or outcomes research |
3a | SR (with homogeneity*) of case-control studies | Â | SR (with homogeneity*) of 3b and better studies | SR (with homogeneity*) of 3b and better studies | SR (with homogeneity*) of 3b and better studies |
3b | Individual Case-Control Study | Â | Non-consecutive study; or without consistently applied reference standards | Non-consecutive cohort study, or very limited population | Analysis based on limited alternatives or costs, poor quality estimates of data, but including sensitivity analyses incorporating clinically sensible variations. |
4 | Case-series (and poor quality cohort and case-control studies§§) | Case-series (and poor quality prognostic cohort studies***) | Case-control study, poor or non-independent reference standard | Case-series or superseded reference standards | Analysis with no sensitivity analysis |
5 | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" | Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles" | Expert opinion without explicit critical appraisal, or based on economic theory or "first principles" |