Table 1

Evidence-grading system for clinical practice recommendations

ADA classification system
Level of evidenceDescription
AClear evidence from well-conducted, generalizable, randomized, controlled trials that are adequately powered, including
  • Evidence from a well-conducted multicenter trial

  • Evidence from a meta-analysis that incorporated quality ratings in the analysis

Compelling nonexperimental evidence, i.e., “all-or-none” rule developed by the Centre for Evidence-Based Medicine at Oxford
Supportive evidence from well-conducted, randomized, controlled trials that are adequately powered, including
  • Evidence from a well-conducted trial at one or more institutions

  • Evidence from a meta-analysis that incorporated quality ratings in the analysis

BSupportive evidence from well-conducted cohort studies, including
  • 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
CSupportive evidence from poorly controlled or uncontrolled studies, including
  • 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 high potential for bias (such as case series with comparison with historical controls)

Conflicting evidence with the weight of evidence supporting the recommendation
EExpert consensus or clinical experience
USPSTF recommendation classification system
Estimate of effect
Quality of evidenceSubstantialModerateSmallZero/negative*
    HighABCD
    ModerateBBCD
    LowInsufficient (I)
  • *A study with significant findings against something is given a grade of D.