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Table 2 Australian National Health and Medical Research Council Designated Levels of Evidence1

From: The potential role of the antioxidant and detoxification properties of glutathione in autism spectrum disorders: a systematic review and meta-analysis

Level of evidence Description
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 pseudo-randomised controlled trials (alternate allocation or some other method).
III - 2 Evidence obtained from comparative studies with concurrent controls and allocation not randomised (cohort studies), case control studies or interrupted time series with 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 a case series, either post-test or pre-test and post-test.
  1. 1Data from reference [53]