Table 1.

Strength of clinical evidence

Category A	At least one RCT or meta-analyses of RCTs, or reviews if these contain category A references
Category B	At least one controlled trial without randomization or at least one other type of experimental study, or extrapolated recommendations from RCTs or meta-analyses
Category C	Non-experimental descriptive studies, such as comparative studies, correlational studies, and case-control studies, which are extrapolated from RCTs, non-randomized controlled studies, or other experimental studies
Category D	Expert committee reports or opinions or clinical experience of respected authorities. Also includes all abstracts

RCT randomized control trial