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Table 2

Recommendation grades and scientific level of evidence according to the HAS [1].

Recommendations grade Scientific level of proof from literature
Well established proof
Level 1
High power randomized comparative trials;
Meta-analysis of randomized comparative trials;
Analysis of well conducted studies.
Scientific presumption
Level 2
Low power randomized comparative trials;
Not randomized well conducted comparative studies;
Cohort studies.
C Level 3
Case-control studies.
Low scientific proof Level 4
Comparative trials with number of bias;
Retrospective studies;
Case series;
Descriptive epidemiological studies (transversal, longitudinal).

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