Table 1-3Levels of evidence for intervention 1

Level of evidenceType of evidence
1++High-quality meta-analyses, systematic reviews of RCTs, or RCTs with a very low risk of bias
1+Well-conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias
1Meta-analyses, systematic reviews of RCTs, or RCTs with a high risk of bias*
2++High-quality systematic reviews of case–control or cohort studies
High-quality case–control or cohort studies with a very low risk of confounding, bias or chance and a high probability that the relationship is causal
2+Well-conducted case–control or cohort studies with a low risk of confounding, bias or chance and a moderate probability that the relationship is causal
2Case–control or cohort studies with a high risk of confounding, bias, or chance and a significant risk that the relationship is not causal*
3Non-analytic studies (for example, case reports, case series)
4Expert opinion, formal consensus
*

Studies with a level of evidence ‘–‘ should not be used as a basis for making a recommendation (see section 7.4 of guideline development manual 1

From: 1.3, Methodology

Cover of Alcohol Use Disorders
Alcohol Use Disorders: Diagnosis and Clinical Management of Alcohol-Related Physical Complications [Internet].
NICE Clinical Guidelines, No. 100.
National Clinical Guideline Centre (UK).
Copyright © 2010, National Clinical Guidelines Centre.

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