The American Diabetes Association evidence-grading system for clinical practice recommendations is as follows1:

Level of EvidenceDescription
AClear evidence from well-conducted, generalizable, randomized, controlled trials that are adequately powered, including:
• Multicenter trial
• Meta-analysis incorporating quality ratings
• Compelling nonexperimental evidence, (ie, “all-or-none” rule) developed by the Center for Evidence-Based Medicine at Oxford*
Supportive evidence from well-conducted, randomized, controlled trials that are adequately powered, including:
• Well-conducted trials at ≥1 institutions
BSupportive evidence from well-conducted cohort studies including:
• Prospective cohort studies or registry
• Meta-analysis of cohort studies
Supportive evidence from a well-conducted case-control study.
CSupportive evidence from poorly controlled or uncontrolled studies including:
• Randomized clinical trials with ≥1 major or ≥3 minor methodological flaws that could invalidate the results
• Observational studies with high potential for bias
• Case series or case reports
Conflicting evidence with the weight of evidence supporting the recommendation.
EExpert consensus or clinical experience.
  • * Either all patients died before therapy and at least some survived with therapy or some patients died without therapy and none died with therapy (eg, the use of insulin in the treatment of diabetes ketoacidosis).