Oxford CEBM Levels 5

8/12/2019 Oxford CEBM Levels 5

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Oxford Centre for Evidence-based Medicine Levels of Evidence (May 2001)

Level

Therapy/Prevention,Aetiology/Harm

Prognosis Diagnosis Differential diagnosis/symptomprevalence study

Economic and decision analyses

1a S !"ith homogeneity#

$ of %Ts S !"ithhomogeneity#

$of inception

cohort studies&%D'validated indifferent populations

S !"ithhomogeneity#

$of Level 1

diagnostic studies& %D'"ith 1(studies from different clinical centres

S !"ithhomogeneity#

$ of

prospective cohort studies

S !"ith homogeneity#

$ of Level 1

economic studies

1( )ndividual %T !"ith narro"%onfidence )nterval*

$)ndividual inception cohort study "ith+ -. follo"up& %D'validated ina single population

0alidating## cohort study "ithgood'''reference standards& or%D'tested "ithin one clinicalcentre

Prospective cohort study "ith goodfollo"up####

Analysis (ased on clinically sensi(lecosts or alternatives& systematicrevie"!s$ of the evidence& andincluding multi"ay sensitivityanalyses

1c All or none All or none caseseries A(solute SpPins and Sn2outs'' All or none caseseries A(solute (ettervalue or "orsevalueanalyses ''''

3a S !"ith homogeneity#

$ of cohortstudies

S !"ithhomogeneity#

$of eitherretrospective cohort studies oruntreated control groups in %Ts

S !"ithhomogeneity#

$of Level +3diagnostic studies

S !"ithhomogeneity#

$ of 3( and(etter studies

S !"ith homogeneity#

$ of Level +3economic studies

3( )ndividual cohort study !including lo"4uality %T& e5g5, 6-. follo"up$

etrospective cohort study or follo"up of untreated control patients in an%T& Derivation of%D'orvalidated on splitsample only

E7ploratory## cohort study "ithgood'''reference standards& %D'after derivation, or validated only onsplitsample or data(ases

etrospective cohort study, or poorfollo"up

Analysis (ased on clinically sensi(lecosts or alternatives& limitedrevie"!s$ of the evidence, or singlestudies& and including multi"ay

sensitivity analyses3c 89utcomes8 esearch& Ecological

studies89utcomes8 esearch Ecological studies Audit or outcomes research

:a S !"ith homogeneity#$ of casecontrol studies

S !"ithhomogeneity#$of :( and(etter studies

S !"ithhomogeneity#$ of :( and(etter studies

S !"ith homogeneity#$ of :( and(etter studies

:( )ndividual %ase%ontrol Study 2onconsecutive study& or "ithoutconsistently applied referencestandards

2onconsecutive cohort study, orvery limited population

Analysis (ased on limitedalternatives or costs, poor 4ualityestimates of data, (ut includingsensitivity analyses incorporatingclinically sensi(le variations5

; %aseseries !andpoor 4uality cohortand casecontrol studies$

%aseseries !andpoor 4ualityprognostic cohort studies###$

%asecontrol study, poor or nonindependent reference standard

%aseseries or supersededreference standards

Analysis "ith no sensitivity analysis

< E7pert opinion "ithout e7plicit criticalappraisal, or (ased on physiology,(ench research or 8first principles8

E7pert opinion "ithout e7plicit criticalappraisal, or (ased on physiology,(ench research or 8first principles8



E7pert opinion "ithout e7plicit criticalappraisal, or (ased on economictheory or 8first principles8

Produced (y =o( Phillips, %hris =all, Dave Sac>ett, Doug =adenoch, Sharon Straus, =rian Haynes, ?artin Da"es since 2ovem(er 1@@5
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Notessers can add a minussign 88 to denote the level of that fails to provide a conclusive ans"er (ecause ofB

E)THE a single result "ith a "ide %onfidence )nterval !such that, for e7ample, an A in an %T is not statistically significant (ut "hose confidence intervals fail to e7clude clinically important

(enefit or harm$

9 a Systematic evie" "ith trou(lesome !and statistically significant$ heterogeneity5

Such evidence is inconclusive, and therefore can only generate Crade D recommendations5

# =y homogeneity "e mean a systematic revie" that is free of "orrisome variations !heterogeneity$ in the directions and degrees of results (et"een individual studies5 2ot all systematicrevie"s "ith statistically significant heterogeneity need (e "orrisome, and not all "orrisome heterogeneity need (e statistically significant5 As noted a(ove, studies displaying "orrisomeheterogeneity should (e tagged "ith a 88 at the end of their designated level5

' %linical Decision ule5 !These are algorithms or scoring systems "hich lead to a prognostic estimation or a diagnostic category5 $

* See note 3 for advice on ho" to understand, rate and use trials or other studies "ith "ide confidence intervals5

?et "hen all patients died (efore the 7 (ecame availa(le, (ut some no" survive on it& or "hen some patients died (efore the 7 (ecame availa(le, (ut none no" die on it5

=y poor 4uality cohort study "e mean one that failed to clearly define comparison groups and/or failed to measure e7posures and outcomes in the same !prefera(ly (linded$, o(ective "ayin (oth e7posed and none7posed individuals and/or failed to identify or appropriately control >no"n confounders and/or failed to carry out a sufficiently long and complete follo"up ofpatients5 =y poor 4uality casecontrol study "e mean one that failed to clearly define comparison groups and/or failed to measure e7posures and outcomes in the same !prefera(ly(linded$, o(ective "ay in (oth cases and controls and/or failed to identify or appropriately control >no"n confounders5

Splitsample validation is achieved (y collecting all the information in a single tranche, then artificially dividing this into 8derivation8 and 8validation8 samples5

'' An 8A(solute SpPin8 is a diagnostic finding "hose Specificity is so high that a Positive result rulesin the diagnosis5 An 8A(solute Sn2out8 is a diagnostic finding "hose Sensitivity is so high

that a 2egative result rulesout the diagnosis5** Cood, (etter, (ad and "orse refer to the comparisons (et"een treatments in terms of their clinical ris>s and (enefits5

''' Cood reference standards are independent of the test, and applied (lindly or o(ectively to applied to all patients5 Poor reference standards are haphaFardly applied, (ut still independent ofthe test5 se of a nonindependent reference standard !"here the GtestG is included in the GreferenceG, or "here the GtestingG affects the GreferenceG$ implies a level ; study5

''''

=ettervalue treatments are clearly as good (ut cheaper, or (etter at the same or reduced cost5 orsevalue treatments are as good and more e7pensive, or "orse and the e4ually or moree7pensive5

## 0alidating studies test the 4uality of a specific diagnostic test, (ased on prior evidence5 An e7ploratory study collects information and tra"ls the data !e5g5 using a regression analysis$ to find"hich factors are GsignificantG5

### =y poor 4uality prognostic cohort study "e mean one in "hich sampling "as (iased in favour of patients "ho already had the target outcome, or the measurement of outcomes "asaccomplished in 6-. of study patients, or outcomes "ere determined in an un(linded, nono(ective "ay, or there "as no correction for confounding factors5

#### Cood follo"up in a differential diagnosis study is +-., "ith ade4uate time for alternative diagnoses to emerge !eg 1I months acute, 1 < years chronic$

Grades of Recommendation

consistent level 1 studies! consistent level 3 or : studies ore7trapolations from level 1 studiesC level ; studies ore7trapolations from level 3 or : studies

" level < evidence or trou(lingly inconsistent or inconclusive studies of any level


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"Extrapolations" are where data is used in a situation which has potentially clinically important differences than the original study situation.

Oxford CEBM Levels 5

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