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Levels of Evidence and Grades of Recommendations

 

Evidence Based Health Care -- Practice guidelines levels of evidence and grades of recommendations used by the National Guideline Clearinghouse

Levels of Evidence:

IA

Evidence from meta-analysis of randomized controlled trials

IB

Evidence from at least one randomized controlled trial

IIA

Evidence from at least one controlled study without randomization

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 or clinical experience of respected authorities, or both


Grades of Recommendations:

A

Directly based on Level I evidence

BDirectly based on Level II evidence or extrapolated recommendations from Level I evidence
CDirectly based on Level III evidence or extrapolated recommendations from Level I or II evidence
DDirectly based on Level IV evidence or extrapolated recommendations from Level I, II, or III evidenc


(from Shekelle PG, Woolf SH, Eccles M, Grimshaw J. Developing clinical guidelines. West J Med. 170(6):348-51, 1999 June)

 

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