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Centre for Evidence-
Based Medicine

Does providing evidence-based care improve outcomes for patients?

No such evidence is available from randomized trials because no investigative team or research granting agency has yet overcome the problems of sample-size, contamination, blinding, and long-term follow-up which such a trial requires. Moreover, there are ethical concerns with such a trial: is withholding access to evidence from the control clinicians ethical? On the other hand, population-based "outcomes research" has repeatedly documented that those patients who do receive evidence-based therapies have better outcomes than those who don't.

For positive examples, myocardial infarction survivors prescribed aspirin or beta-blockers have lower mortality rates than those who aren't prescribed these drugsi,ii, and where clinicians use more warfarin and stroke unit referrals, stroke mortality declines by >20%iii. For a negative example, patients undergoing carotid surgery despite failing to meet evidence-based operative criteria, when compared with operated patients who meet those criteria, are more than 3 times as likely to suffer major stroke or death in the next monthiv.


  1. Krumholz HM, Radford MJ, Ellerbeck EF, Hennen J, Meehan TP, Petrillo M, et al. Aspirin for secondary prevention after acute myocardial infarction in the elderly: prescribed use and outcomes. Ann Intern Med 1996;124:292-8.
  2. Krumholz HM, Radford MJ, Wang Y, Chen J, Heiat A, Marciniak TA. National use and effectiveness of beta-blockers for the treatment of elderly patients after acute myocardial infarction. National Cooperative Cardiovascular Project. JAMA 1998;280:623-9.
  3. Mitchell JB, Ballard DJ, Whisnant JP, Ammering CJ, Samsa GP, Matchar DB: What role do neurologists play in determining the costs and outcomes of stroke patients? Stroke.1996;27: 1937-43
  4. Wong JH, Findlay JM, Suarez-Almazor ME. Regional performance of carotid endarterectomy appropriateness, outcomes and risk factors for complications. Stroke 1997;28:891-8.