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hierarchy of evidence


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The Canadian Task Force on the Periodic Health Examination (1994) reviewed published work on the efficacy of preventive methods, and devised a method to assess the quality of the evidence, as follows:I. (Best quality) Evidence from at least one properly designed randomized controlled trial (RCT).II-1. Evidence from well-designed controlled trials without randomization.II-2. Evidence from well-designed cohort or case control studies, preferably from more than one center or research group.II-3. Evidence from multiple time series with or without the intervention; dramatic results from uncontrolled experiments, e.g., first use of rabies vaccine in 1885, penicillin in the 1940s.III. Opinions of respected authorities based on clinical experience, descriptive studies, reports of expert committees, consensus conferences, etc.It is not always possible to achieve complete scientific rigor; partly because sometimes randomized trials may not be feasible or may be unethical.

I. (Best quality) Evidence from at least one properly designed randomized controlled trial (RCT).

II-1. Evidence from well-designed controlled trials without randomization.

II-2. Evidence from well-designed cohort or case control studies, preferably from more than one center or research group.

II-3. Evidence from multiple time series with or without the intervention; dramatic results from uncontrolled experiments, e.g., first use of rabies vaccine in 1885, penicillin in the 1940s.

III. Opinions of respected authorities based on clinical experience, descriptive studies, reports of expert committees, consensus conferences, etc.

Subjects: Public Health and Epidemiology.


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