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Table 1—

ADA evidence grading system for clinical practice recommendations

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 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 
 • Evidence from a well-conducted prospective cohort study or registry 
 • Evidence from a well-conducted prospective cohort study 
 • 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 
 • 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 to 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 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 
 • Evidence from a well-conducted prospective cohort study or registry 
 • Evidence from a well-conducted prospective cohort study 
 • 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 
 • 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 to 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 prior to 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 DKA.

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