Table 2

ADA evidence grading system for clinical practice recommendations (4)

Level of EvidenceDescription
AClear 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

BSupportive 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
CSupportive 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
EExpert consensus or clinical experience