Evidence obtained from a systematic review of all relevant randomized controlled trials
Evidence obtained from at least one properly designed randomized controlled trial
Evidence obtained from well-designed pseudo-randomized controlled trials (alterative allocation or some other method)
Evidence obtained from comparative studies with concurrent controls and allocation not randomized (cohort studies), case–control studies, or interrupted time series with a control group
Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel control group
Evidence obtained from case series, either post-test or pre-test and post-test.