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Table 1 The hierarchy of evidence from the centre for evidence-based-medicine

From: Italian guidelines for management and treatment of hyperbilirubinaemia of newborn infants ≥ 35 weeks’ gestational age

Level

Definition

1a

Systematic review (with homogeneity) of RCTs

1b

Individual RCT (with narrow confidence interval)

2a

Systematic review (with homogeneity) of cohort studies

2b

Individual cohort study

3a

Systematic review (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”