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1、Oxford Centre for Evidence-based Medicine Levels of Evidence (May 2001)LevelTherapy/Preve ntio n, Aetiology/HarmPrognosisDiagnosisDifferential diagnosis/symptom prevalence studyEconomic and decision analyses1aSR (with homogeneity*) of RCTsSR (with homogeneity*) of inception cohort studies; CDR 十 val
2、idated in different populationsSR (with homogeneity*) of Level 1 diagnostic studies; CDRf 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
3、inception cohort study with 80% follow-up; CDRf validated in a single populationValidating* cohort study with goodfff reference standards; or CDRf tested within one clinical centreProspective cohort study with good follow-up*Analysis based on clinically sensible costs or alternatives; systematic rev
4、iew(s) of the evidence; and including multi-way sensitivity analyses1cAll or noneAll or none case-seriesAbsolute SpPins and SnNoutsffAll or none case-seriesAbsolute better-value or worse-value analyses ffff2aSR (with homogeneity*) of cohort studiesSR (with homogeneity*) of either retrospective cohor
5、t 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 fo
6、llowup of untreated control patients in an RCT; Derivation of CDRf or validated on split-sample onlyExploratory* cohort study with goodfffreference standards; CDRf after derivation, or validated only on split-sample or databasesRetrospective cohort study, or poor follow-upAnalysis based on clinicall
7、y sensible costs or alternatives; limited review(s) of the evidence, or single studies; and including multi-way sensitivity analyses2cOutcomes Research; Ecological studiesOutcomes ResearchEcological studiesAudit or outcomes research3aSR (with homogeneity*) of casecontrol studiesSR (with homogeneity*
8、) of 3b and be Iter studiesSR (with homogeneity*) of 3b and be Iter studiesSR (with homogeneity*) of 3b and be Iter studies3bIndividual Case-Control StudyNon-consecutive study; or without consistently applied reference standardsNon-consecutive cohort study, or very limited populationAnalysis based o
9、n limited alternatives or costs, poor quality estimates of data, but including sensitivity analyses incorporating clinically cencible variations4Case-series (and poor quality cohort and case control studies)Case-series (and poor quality prognostic cohort studies*)Case-control study, poor or nonindep
10、endent reference standardCase-series or superseded reference standardsAnalysis with no sensitivity analysis5Expert opinion without explicit critical appraisal, or based on physiology, bench research or first principlesExpert opinion without explicit critical appraisal, or based on physiology, bench
11、research or first principlesExpert opinion without explicit critical appraisal, or based on physiology, bench research or first principlesExpert opinion without explicit critical appraisal, or based on physiology, bench research or first principlesExpert opinion without explicit critical appraisal,
12、or based on economic theory or first principlesProduced by Bob Phillips, Chris Ball, Dave Sackett, Doug Badenoch, Sharon Straus, Brian Haynes, Martin Dawes since November 1998.NotesUsers can add a minus-sign - to denote the level of that fails to provide a conclusive answer because of: EITHER a sing
13、le result with a wide Confidence Interval (such that, for example, an ARR in an RCT is not statistically significant but whose confidence intervals fail to exclude clinically important benefit or harm) OR a Systematic Review with troublesome (and statistically significant) heterogeneity. Such eviden
14、ce is inconclusive, and therefore can only generate Grade D recommendations.*By homogeneity we mean a systematic review that is free of worrisome variations (heterogeneity) in the directions and degrees of results between individual studies. Not all systematic reviews with statistically significant
15、heterogeneity need be worrisome, and not all worrisome heterogeneity need be statistically significant. As noted above, studies displaying worrisome heterogeneity should be tagged with a - at the end of their designated level+Clinical Decision Rule (These are algorithms or scoring systems which lead to a prognostic estimation or a diagnostic category )1 +See note #2 for advice on how to understand rate and use trials or other studies with wide confidence intervalsT&let when all patients died before the Rx became available but some now survive on 计 or when some patients died b
