Levels of evidence is a ranking system used in evidence-based practices to describe the strength of the results measured in a clinical trial or research study. The design of the study (such as a case report for an individual patient or a double-blinded randomized controlled trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence. Levels of evidence range from I-IV.
- Ia - Evidence from Meta-analysis of Randomized Controlled Trials
- Ib - Evidence from at least one Randomized Controlled Trials
- IIa - Evidence from at least one well designed controlled trial which is not randomized
- IIb - Evidence from at least one well designed experimental trial
- III - Evidence from case, correlation, and comparative studies.
- IV - Evidence from a panel of experts
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“Pushkin’s composition is first of all and above all a phenomenon of style, and it is from this flowered rim that I have surveyed its seep of Arcadian country, the serpentine gleam of its imported brooks, the miniature blizzards imprisoned in round crystal, and the many-hued levels of literary parody blending in the melting distance.”
—Vladimir Nabokov (1899–1977)
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