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Table 1 Scottish Intercollegiate Guideline Network (SIGN) grading of evidence, with equivalent simplified categorization used for present analysis

From: Evidence-based practice in Behçet’s disease: identifying areas of unmet need for 2014

Level of evidence Description Categorisation in this analysis
1++ High quality meta-analyses, systematic reviews of RCTs, or RCTs with a very low risk of bias 1
1+ Well conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias  
1- Meta-analyses, systematic reviews or RCTs, or RCTs with a high risk of bias  
2++ High quality systematic reviews of case-control or cohort studies or 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
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 causal  
3 Non-analytic studies, e.g. case reports, case series 3
4 Expert opinion 4