OCEBM Levels of Evidence

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Levels of evidenceIntroduction

NB: the table is intended to be used alongside the Introductory Document and Background Document. Please do not read the table separately but rather read the Introductory Document and Table together.

Hierarchies of evidence have been somewhat inflexibly used, and criticised, for some decades. The CEBM “levels of evidence” were first produced in 1998 for Evidence-Based On Call to make the process of finding appropriate evidence feasible and its results explicit. We have revised the “levels” in light of new concepts and data, and we would like to hear your feedback.

There are two different ways to interpret Level 1 evidence for treatment benefits as it is currently stated. The intended interpretation is: “either N-of-1 randomized trials or systematic reviews of randomized trials”. The wrong interpretation is: “either systematic reviews of randomized trials or systematic reviews of n-of-1 trials”.

Click here to see the OCEBM Table of Evidence Glossary of Terms


 

Table: results of a PubMed search for “atrial fibrillation AND warfarin” with some filters

Type Term used Number of articles
All articles  (no filter) 2175
RCT “random allocation” [MeSH] 7
cohort “cohort studies” [MeSH] 366
Case-control “Case-Control Studies”[Mesh] 234
Case report Case Reports [Publication Type] 196

(search done Jan 7th 2010)

Full list of Downloads

Citing Levels of Evidence 2

If you intend to cite this table and/or the accompanying text please use one of the following citation examples.

How to cite the Levels of Evidence 2 Table

OCEBM Levels of Evidence Working Group*. “The Oxford Levels of Evidence 2″.
Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/index.aspx?o=5653

* OCEBM Levels of Evidence Working Group = Jeremy Howick, Iain Chalmers (James Lind Library), Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, Hazel Thornton, Olive Goddard and Mary Hodgkinson

How to cite the Introductory Document

Jeremy Howick, Iain Chalmers, Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, and Hazel Thornton. “The 2011 Oxford CEBM Levels of Evidence (Introductory Document)”.
Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/index.aspx?o=5653

How to cite the Background Document

Jeremy Howick, Iain Chalmers, Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, and Hazel Thornton. “Explanation of the 2011 Oxford Centre for Evidence-Based Medicine (OCEBM) Levels of Evidence (Background Document)”.
Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/index.aspx?o=5653

References

Ball CM, Phillips RS. Evidence-Based On-Call. Churchill Livingstone: Edinburgh, 2001.

Guyatt, G.H., et al., GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ, 2008. 336(7650): p. 924-6.