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. 2020 Apr 10;15:90. doi: 10.1186/s13023-020-01366-z

Table 5.

Levels of evidence according to the French Health Authority guidelines

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