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Table 1 Categories of evidence in studies

From: The Brazilian Society of Rheumatology recommendations on investigation and diagnosis of systemic autoimmune myopathies

Levels Evidence
1a Systematic review and RCT meta-analysis
1b At least one RCT with narrow confidence interval
2a Systematic review and meta-analysis of cohort studies
2b At least one cohort study or low quality RCT
3a Systematic review and meta-analysis of case-control studies
3b At least one case control study
4 At least one case series or cohort study and low quality case-control studies
5 Expert opinion without critical evaluation explicit or based on physiology, bench research or “fundamental principles”
  1. RCT randomized clinical trial