Table 2.2Grading the evidence statements and recommendations

Levels of evidenceClassification of recommendations
LevelType of evidenceClassEvidence
1++High-quality meta-analysis (MA), systematic reviews (SR) of randomised controlled trials (RCTs), or RCTs with a very low risk of biasALevel 1++ and directly applicable to the target population

or

Level 1+ and directly applicable to the target population AND consistency of results

Evidence from NICE technology appraisal
1+Well-conducted MA, SR or RCTs, or RCTs with a low risk of bias
1−MA, SR of RCTs, or RCTs with a high risk of biasNot used as a basis for making a recommendation
2++High-quality SR 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
BLevel 2++, directly applicable to the target population and demonstrating overall consistency of results

or

Extrapolated evidence from 1++ or 1+
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
2−Case-control or cohort studies with a high risk of confounding, bias or chance and a significant risk that the relationship is not causalNot used as a basis for making a recommendation
3Non-analytic studies (for example case reports, case series)CLevel 2+, directly applicable to the target population and demonstrating overall consistency of results

or

Extrapolated evidence from 2++
4Expert opinion, formal consensusDLevel 3 or 4

or

Extrapolated from 2+

or

Formal consensus
D (GPP)A good practice point (GPP) is a recommendation based on the experience of the GDG

Diagnostic study level of evidence and classification of recommendation was also included.1

From: 2, Methodology

Cover of Parkinson's Disease
Parkinson's Disease: National Clinical Guideline for Diagnosis and Management in Primary and Secondary Care.
NICE Clinical Guidelines, No. 35.
National Collaborating Centre for Chronic Conditions (UK).
Copyright © 2006, Royal College of Physicians of London.

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