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Hierarchy of Clinical Evidence . Systematic Reviews Metaanalysis Double-blind Randomized Controlled Trials Cohort Studies Case-Control St udies Cases Report/Series. Physiologic Studies Intuition or Beliefs. Observational. Design of a cohort study. TIME direction of inquiry
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Hierarchy of Clinical Evidence Systematic Reviews Metaanalysis Double-blindRandomized Controlled Trials Cohort StudiesCase-Control StudiesCases Report/Series Physiologic Studies Intuition or Beliefs Observational
Design of a cohort study TIME direction of inquiry people exposed disease population without the no disease disease not exposed disease no disease “at risk”
Design of a case-control study TIME direction of inquiry Start with: Exposed cases (people with disease) Not exposed Population Exposed controls (people without disease) Not exposed
Questions to ask when an association is reported in the literature (eg estrogen and CHD) Explanation Finding Association Bias in selection Yes No or measurement Chance Likely Unlikely Confounding Yes No Cause Cause
Case report? Association and cause Explanation Finding Association Bias in selection Yes No or measurement Chance Likely Unlikely Confounding Yes No Cause Cause Case series?
Association and cause Explanation Finding Association Bias in selection Yes No or measurement Chance Likely Unlikely Confounding Yes No Cause Cause P value
Association and cause Explanation Finding Association Bias in selection Yes No or measurement Chance Likely Unlikely Confounding Yes No Cause Cause
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)
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
Hierarchy of study methods for clinical decision-making Systematic reviews
Is observational evidence equivalent to experimental evidence? Benson NEJM 2000;342:1877 Concato NEJM 2000;342:1887 In some cases -YES In others- NO !
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
How much of Medicine is Evidence-Based ? Matzen P. Ugeskr laeger 2003;165:1431-5 • General Internal Medicine - 50% • Psychiatry- 65% • Others (surgery, general practice, dermatology) - less Lai 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)
Clinical trials Should not be performed unless there is a realistic chance of providing a valid/reliable answer to a well-defined medical question
But…SHEP study Of 447,921 (100%)identified 31,960 (11.6%)met initial criteria 4,736 (1.03%)randomized
% of Pop Men, gen’l pop DM CVD CHF MI Angina Wom., gen’l pop SHEP pop
Coke tastes better…….! Than what?
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 CAVEATS in using RCT evidence to guide patient management
Don’t drown in the evidence ACP J Club, Bandolier, POEMS, clinical evidence, Cochrane Reviews, Clinical guidelines clearinghouse Use predigested sources