Table 2

Hierarchy of research for treatment studies

Ia:Evidence from a systematic review of randomised controlled trials
Ib:Evidence from at least one randomised controlled trial
IIa:Evidence from at least one controlled study without randomisation
IIb:Evidence from at least one other type of quasi-experimental study
III:Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies, and case control studies
IV:Evidence from expert committee reports or opinions and/or clinical experience of respected authorities