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Table 1—

ADA evidence grading system for clinical practice recommendations [reprinted from Diabetes Care 26 (Suppl. 1):S1, 2003]

Level of evidenceDescription
Clear 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 Center 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

 
Supportive 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 
Supportive 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)

  • Evidence from case series or case reports

 
 Conflicting evidence with the weight of evidence supporting the recommendation 
Expert consensus or clinical experience 
Level of evidenceDescription
Clear 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 Center 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

 
Supportive 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 
Supportive 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)

  • Evidence from case series or case reports

 
 Conflicting evidence with the weight of evidence supporting the recommendation 
Expert 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. Example: use of insulin in the treatment of diabetic ketoacidosis.

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