Skip to main content
. Author manuscript; available in PMC: 2011 Aug 1.
Published in final edited form as: Nutr Rev. 2010 Aug;68(8):439–458. doi: 10.1111/j.1753-4887.2010.00304.x

Table 2.

Categories of evidence in evaluating the quality of reports

Category Classification Description
Ia Strong Evidence from a meta-analysis of randomized, controlled trials
Ib Strong Evidence from at least one randomized, controlled trial
IIa Less Strong Evidence from at least one controlled study without randomization
IIb Less Strong Evidence from at least one other type of quasi-experimental study
III Weaker Evidence from descriptive studies, such as comparative studies, correlation studies, and case control studies
IV Weaker Evidence from expert committee reports, opinions or clinical experience of respected authorities, or both
Inconsistent Evidence from small studies that are inconsistent in outcome
Speculative Posited relationships are based essentially on extrapolation from mechanism

Adapted from Manz 104