Table 2.

ADA evidence grading system for clinical practice recommendations (4)

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 (i.e., “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 one or more 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 one or more major or three or more minor methodological flaws that could invalidate the results • Evidence from observational studies with a high potential for bias (e.g., 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