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Table 1 Recommendation grading (according to the "Guide d’analyse de la littérature et gradation des recommandations" - Literature analysis and recommendation grading guide, HAS, January 2000)

From: Medical follow-up for workers exposed to bladder carcinogens: the French evidence-based and pragmatic statement

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