Table 2.

ADA Evidence Grading System for Clinical Practice Recommendations⁴

Level of Evidence	Description
A	Clear evidence from well-conducted, generalizable RCTs that are adequately powered, including the following:  Evidence from a well-conducted multicenter trial  Evidence from a meta-analysis that incorporated quality ratings into the analysis
	Compelling nonexperimental evidence (ie, “all or none” rule developed by the Centre for Evidence-Based Medicine at the University of Oxford)
	Supportive evidence from well-conducted RCTs that are adequately powered, including the following:  Evidence from a well-conducted trial at ≥1 institutions  Evidence from a meta-analysis that incorporated quality ratings into the analysis
B	Supportive evidence from well-conducted cohort studies  Evidence from a well-conducted prospective, cohort study or registry  Evidence from a well-conducted meta-analysis of cohort studies
	Supportive evidence from a well-conducted case-control study
C	Supportive evidence from poorly controlled or uncontrolled studies  Evidence from randomized clinical trials with ≥1 major or ≥3 minor methodological flaws that could invalidate the results  Evidence from observational studies with a high potential for bias (eg, case series with comparison with historical control subjects)  Evidence from case series or case reports
	Conflicting evidence with the weight of evidence supporting the recommendation
E	Expert consensus or clinical experience

ADA indicates American Diabetes Association; and RCT, randomized, controlled trial.