Table 2 Levels of evidence and grading of recommendations (National Health and Medical Research Council 1999 [19])

I

Evidence obtained from a systematic review of all relevant randomized controlled trials

II

Evidence obtained from at least one properly designed randomized controlled trial

III-1

Evidence obtained from well-designed pseudo-randomized controlled trials (alterative allocation or some other method)

III-2

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

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 and post-test.