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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
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
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
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
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

association and 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 cause6
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 cause7
Association and cause

Explanation Finding

Association

Bias in selection Yes No

or measurement

Chance Likely Unlikely

Confounding Yes No

Cause Cause

criteria for causation
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
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

is observational evidence equivalent to experimental evidence

Is observational evidence equivalent to experimental evidence?

Benson NEJM 2000;342:1877

Concato NEJM 2000;342:1887

In some cases -YES

In others- NO !

slide12

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
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
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
But…SHEP study

Of 447,921 (100%)identified

31,960 (11.6%)met initial criteria

4,736 (1.03%)randomized

slide17

% of Pop

Men, gen’l pop

DM CVD CHF MI Angina

Wom., gen’l pop

SHEP pop

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

CAVEATS in using RCT evidence to guide patient management
don t drown in the evidence
Don’t drown in the evidence

ACP J Club, Bandolier, POEMS, clinical evidence, Cochrane Reviews, Clinical guidelines clearinghouse

Use predigested sources