Oxford Centre for Evidence-based Medicine – Levels of Evidence (March 2009).docx

Oxford Centre for Evidence-based Medicine – Levels of Evidence (March 2009)What are we to do when the irresistible force of the need to offer clinical advice meets with the immovable object of flawed evidence? All we can do is our best: give the advice, but alert the advisees to the flaws in the evidence on which it is based.The CEBM ‘Levels of Evidence 1′ document sets out one approach to systematising this process for different question types.(For definitions of terms used see our glossary)LevelTherapy / Prevention, Aetiology / HarmPrognosisDiagnosisDifferential diagnosis / symptom prevalence studyEconomic and decision analyses1aSR (with homogeneity*) of RCTsSR (with homogeneity*) of inception cohort studies; CDR”? validated in different populationsSR (with homogeneity*) of Level 1 diagnostic studies; CDR”? with 1b studies from different clinical centresSR (with homogeneity*) of prospective cohort studiesSR (with homogeneity*) of Level 1 economic studies1bIndividual RCT (with narrow Confidence Interval”?)Individual inception cohort study with 80% follow-up; CDR”? validated in a single populationValidating** cohort study with good”?”?”? reference standards; or CDR”? tested within one clinical centreProspective 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 analyses1cAll or none§All or none case-seriesAbsolute SpPins and SnNouts”?“All or none case-seriesAbsolute better-value or worse-value analyses ”?”?”?“2aSR (with homogeneity*) of cohort studiesSR (with homogeneity*) of either retrospective cohort studies or untreated control groups in RCTsSR (with homogeneity*) of Level 2 diagnostic studiesSR (with homogeneity*) of 2b and better studiesSR (with homogeneity*) of Level 2 economic studies2bIndividual cohort study (including low quality RCT; e.g., 80% follow-up)Retrospective cohort study or follow-up of untreated control patients in an RCT; Der