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I
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Evidence obtained from a systematic review of all relevant randomised controlled trials.
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II
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Evidence obtained from at least one properly designed randomised controlled trial.
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III-1
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Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method.
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III-2
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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.
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III-3
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Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel control group.
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IV
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Evidence obtained from case series, either post-test or pre-test/post-test.
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