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Level of Evidence

Version Oxford 2011

The Oxford Centre for Evidence-Based Medicine (OCEBM) 2011 Levels of Evidence is a framework used to rate the quality and strength of evidence in medical research and clinical practice. This system was created by the Oxford Centre for Evidence-Based Medicine to guide clinicians and researchers in assessing the reliability of evidence when making medical decisions. The 2011 version offers a granular approach, categorizing levels based on the type of clinical question (e.g., therapy vs. diagnosis), which makes it useful for selecting studies specific to various types of medical queries.

Clinicians use the OCEBM Levels of Evidence to assess the quality of studies when reviewing medical literature. Higher-level evidence (Levels 1 and 2) is generally prioritized in clinical decision-making, whereas lower-level evidence (Levels 4 and 5) is relied upon when stronger studies are unavailable. This system helps clinicians make evidence-based choices, supporting patient outcomes through research-backed practices.

Tabelle X

i Level may be graded down on the basis of study quality, imprecision, indirectness (study PICO does not match questions PICO), because of inconsistency between studies, or because the absolute effect size is very small; Level may be graded up if there is a large or very large effect size.

ii As always, a systematic review is generally better than an individual study.

Reference: http://www.cebm.net/index.aspx?o=5653

• OCEBM Table 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

Version Oxford 2008

The Oxford Centre for Evidence-Based Medicine (OCEBM) 2008 Levels of Evidence is an earlier framework designed to categorize the quality of medical evidence based on study design and reliability. Like the 2011 update, it was created to help clinicians assess the strength of evidence when making healthcare decisions. The 2008 version ranks evidence according to study type.

The 2008 levels are organized from Level 1 (highest quality) to Level 5 (lowest quality).

Level Therapy / Prevention, Aetiology / Harm

1a

• SR (with homogeneity) of RCTs

1b

• Individual RCT (with narrow Confidence Interval”)

1c

• All or none

2a

• SR (with homogeneity) of cohort studies

2b

• Individual cohort study (including low quality RCT; e.g., <80% follow-up)

2c

• “Outcomes” Research; Ecological studies

3a

• SR (with homogeneity) of case-control studies

3b

• Individual Case-Control Study

4

• Case-series (and poor quality cohort and case-control studies)

5

• Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles”