Level of evidence | Criteria |
---|---|
Level 1 | Comparative and randomised studies with appropriate statistical power Meta-analyses of randomised studies |
Level 2 | Comparative and randomised studies with limited statistical power Non-randomised studies with high methodological value Cohort studies |
Level 3 | Case-controls studies |
Level 4 | Comparative studies with known bias (selection, inclusion, convenience sampling) Retrospective studies |