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Table 1 Designations of levels of evidence [1]

From: Extending an evidence hierarchy to include topics other than treatment: revising the Australian 'levels of evidence'

Level of evidence Study design
I Evidence obtained from a systematic review of all relevant randomised controlled trials
II Evidence obtained from at least one properly-designed randomised controlled trial
III-1 Evidence obtained from well-designed pseudorandomised controlled trials (alternate allocation or some other method)
III-2 Evidence obtained from comparative studies (including systematic reviews of such studies) with concurrent controls and allocation not randomised, cohort studies, case-control studies, or interrupted time series with a control group
III-3 Evidence obtained from comparative studies with historical control, two or more single arm studies, or interrupted time series without a parallel control group
IV Evidence obtained from case series, either post-test or pre-test/post-test