Evidence-Based Treatment of Cerebrovascular Disease

Introduction to Evidence-Based Medicine

William J. Powers, M.D.-- Departments of Neurology, Neurosurgery and Radiology
Washington University School of Medicine -- Presented July 11, 2006

Risk Reduction

Risk without therapy
(baseline risk): X

Risk with therapy: Y

Absolute risk reduction
(risk difference): X - Y

20/100 = 0.20 or 20%

15/100=0.15 or 15%

0.20-0.15 = 0.05

Relative Risk: Y/X

Relative Risk Reduction (RRR)
[1 - (Y/X)] x 100% or [(X-Y)[X] x 100%

0.15/0/20 = 0/75

[1-0.75] x 100% = 25%
[0.05/20] x 100% = 25%

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All References

References

Jaeschke R, Guyatt GH, Sackett DL. Users' guides to the medical literature. II. How to use an article about therapy or prevention. B. What were the results and will they help me in caring for my patients? Evidence-Based Medicine Working Group.
JAMA 1994; 271:59-63.