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Table 1

ADA evidence-grading system for “Standards of Medical Care in Diabetes”

Level of evidenceDescription
A 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 Centre for Evidence-Based Medicine at the University of 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 
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 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 
E Expert consensus or clinical experience 
Level of evidenceDescription
A 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 Centre for Evidence-Based Medicine at the University of 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 
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 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 
E Expert consensus or clinical experience 
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