Classification of Evidence

Evidence levelDescription
Ia:evidence from meta-analysis 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

From: 2, Guideline development

Cover of Clinical Guidelines for the Classification and Care of Women at Risk of Familial Breast Cancer in Primary, Secondary and Tertiary Care
Clinical Guidelines for the Classification and Care of Women at Risk of Familial Breast Cancer in Primary, Secondary and Tertiary Care [Internet].
NICE Clinical Guidelines, No. 14.
School of Health and Related Research (ScHARR), University of Sheffield.
Sheffield (UK): University of Sheffield; 2004 May.
Copyright © 2004, School of Health and Related Research (ScHARR), University of Sheffield.

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