Table 1.

LEVELS OF SCIENTIFIC EVIDENCE

I	Evidence from several randomised controlled clinical trials, systematic reviews of randomised trials and/or international guidelines
II	Evidence from one adequately designed randomised clinical trial
III	Evidence from non-randomised cohort studies with concurrent or historical controls, or meta-analyses including this type of studies
IV	Evidence from retrospective case-controlled studies, or meta-analyses including this type of studies
V	Evidence from case series with no control group
VI	Evidence based on the opinion of recognised experts or expert panels, as indicated in guidelines or consensus conferences, based on the opinion of the panel.