Critical Appraisal Louis Muller October 2009. EBM – Hierarchy of Evidence.
Hierarchy of Clinical Evidence
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Transcript of Hierarchy of Clinical Evidence
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Physiologic StudiesPhysiologic StudiesIntuition or BeliefsIntuition or Beliefs
Systematic Reviews Systematic Reviews MetaanalysisMetaanalysisDouble-blindDouble-blind
Randomized Controlled TrialsRandomized Controlled TrialsCohort StudiesCohort Studies
Case-Control Case-Control StStudiesudiesCases Report/SeriesCases Report/Series
Hierarchy of Clinical Evidence Hierarchy of Clinical Evidence Obs
ervati
onal
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Design of a cohort studyTIME
direction of inquiry
people exposed diseasepopulation without the no disease disease not exposed disease no disease“at risk”
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Design of a case-control study
TIMEdirection of inquiry Start with:
Exposed cases (people with disease)Not exposed
PopulationExposed controls (people without disease)Not exposed
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Questions to ask when an association is reported in the literature
(eg estrogen and CHD)Explanation Finding
Association
Bias in selection Yes Noor measurement
Chance Likely Unlikely
Confounding Yes No
Cause Cause
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Association and causeExplanation Finding
Association
Bias in selection Yes Noor measurement
Chance Likely Unlikely
Confounding Yes No
Cause Cause
Case report?
Case series?
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Association and causeExplanation Finding
Association
Bias in selection Yes Noor measurement
Chance Likely Unlikely
Confounding Yes No
Cause Cause
P value
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Association and causeExplanation Finding
Association
Bias in selection Yes Noor measurement
Chance Likely Unlikely
Confounding Yes No
Cause Cause
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Criteria for causation
1. Is there evidence from true experimentation in humans?
2. Is the association strong?3. Is the association consistent from study to study?4. Is the temporal association correct?5. Is there a dose-response gradient?6. Does the association make biological sense?7. Is the association specific?(Adapted from Bradford Hill)
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Randomization
1. Guarantees equal probability of receiving control/experimental treatment to all participants (removes investigator bias)
2. Protects against imbalances in known and unknown confounders
3. Provides basis for statistical analysis
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Hierarchy of study methods for clinical decision-making
Sys
tem
atic
revi
ews
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Is observational evidence equivalent to
experimental evidence?
Benson NEJM 2000;342:1877Concato NEJM 2000;342:1887
In some cases -YES
In others- NO !
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Clinical trials are selective!-Select group gets in - chance decides who gets treatment; treatment effect decides who does better
Observational evidence is also selective: self-selection of exposure: this may decide who does better
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How much of Medicine is How much of Medicine is Evidence-Based ?Evidence-Based ?
Matzen P. Ugeskr laeger 2003;165:1431-5• General Internal Medicine - 50%• Psychiatry- 65%• Others (surgery, general practice,
dermatology) - lessLai Br. J Ophthal . 2003;4:385-90: • 42.9% of patient interventions were based on
evidence from RCT, meta-analysis or systematic reviews (23% on no evidence)
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Major Disadvantage of RCTs:Selectivity
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Clinical trials
Should not be performed unless there is a realistic chance of providing a valid/reliable answer to a well-defined medical question
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But…SHEP study Of 447,921 (100%) identified
31,960 (11.6%) met initial criteria
4,736 (1.03%) randomized
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01.4
10.1Comorbidity: General Pop
vs. Subgroup
0
5
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20
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12345
AP MI CHF CVA DM
%
of P
op
Men, gen’l pop
Wom., gen’l popSHEP pop
% of Pop
DM CVD CHF MI Angina
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Coke tastes better…….!
Than what?
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Coke tastes better…….!
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CAVEATS in using RCT evidence to guide patient management
1. Tendency to extend application of new treatments to patient groups other that those for whom data exist
2. Extrapolation of data to agents of the same class but untested for specific indication
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Don’t drown in the evidence
Use predigested sources
ACP J Club, Bandolier, POEMS, clinical evidence, Cochrane Reviews, Clinical guidelines clearinghouse
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Good luck!