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Appraising Evidence

Are the results Valid?

  • Was this an appropriate study design to answer the research question?
  • Did it measure what it intended to measure?
  • Did the study have enough power to detect a significant result?
  • Did they include intention to treat?

What are the results?

What re the results in terms of:

  • Magnitude: e.g. overall results do they report NNT RRR etc
  • Significance: are they statically and clinically significant?
  • Do they report CIs and P values?

Are they generalisable to my situation or your title (same thing)

  • Is the intervention feasible in my situation?
  • Could we afford the intervention?

Hierarchy of Evidence

  • Category I:  Evidence from at least one properly randomized controlled trial.
  • Category II-1: Evidence from well-designed controlled trials without randomization.
  • Category II-2: Evidence from well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
  • Category II-3: Evidence from multiple times series with or without intervention or dramatic results in uncontrolled experiments such as the results of the introduction of penicillin treatment in the 1940s.
  • Category III: Opinions of respected authorities, based on clinical experience, descriptive studies and case reports, or reports of expert committees.


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