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Centre for Evidence-
Based Medicine

Are the results of this study valid?

Returning to our clinical scenario from the question formulation tutorial:

You admit a 65 year old man with a stroke. On examination you find that he has mild weakness of the right arm and right leg and bilateral carotid bruits. You send the patient for carotid doppler ultrasonography and subsequently receive the report that he has moderate stenosis (50-69% by NASCET criteria) of the ipsilateral carotid artery. You've noticed in the pile of journals that is accumulating in your office that there has been some recent literature addressing surgical versus medical therapy for patients with symptomatic carotid stenosis but you are unsure of what the results of these studies indicate.

In the tutorial on clinical questions, we formulated the following question: In a 65 year old man with stroke and moderate carotid stenosis, can carotid endarterectomy decrease the risk of stroke compared with medical therapy?

Our search of the literature found article from the Best Evidence (1999;130:33).

How do we critically appraise this therapy paper? We'll start off by considering validity first and the following list outlines the questions that we need to consider when deciding if a therapy paper is valid.

  1. Was the assignment of patients to treatment randomized? And, was the randomization list concealed?
  2. Was follow-up of patients sufficiently long and complete?
  3. Were all patients analyzed in the groups to which they were randomized?

    And some less important points:
  4. Were patients and clinicians kept blind to treatment?
  5. Were groups treated equally, apart from the experimental therapy?
  6. Were the groups similar at the start of the trial?

Do you want to review validity or importance?