Table 2. Categorization of evidence (Eccles and Mason, 2001) (17).

Category	Methodological strength of evidence
I	Meta-analysis of randomized controlled trials (RCT) or at least one RCT
II	A controlled study (non-randomized), other type of quasi-experimental study
III	Nonexperimental 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