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Table 1 Recommendation grading

From: Medical follow-up of workers exposed to lung carcinogens: French evidence-based and pragmatic recommendations

Level of scientific proof provided by the literature (for clinical studies) Recommendation grading
Level 1
High-power randomised comparative studies
Meta-analysis of randomised comparative studies
Decision analysis based on well-conducted studies
A
Scientific proof established
Level 2
Low-power randomised comparative studies
Well-conducted non-randomised comparative studies
Cohort studies
B
Scientific proof presumed
Level 3
Case–control studies
C
Low level of proof
Level 4
Comparative studies with major bias
Retrospective studies
Case series
Descriptive epidemiological studies (cross-sectional, longitudinal)