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TABLE 3

Evidence Levels

LevelDefinition
RCTs or meta-analyses of multiple clinical trials with substantial treatment effects 
RCTs with smaller or less significant treatment effects 
Prospective, controlled, nonrandomized, cohort studies 
Historic, nonrandomized, cohort or case-control studies 
Case series: patients compiled in serial fashion, lacking a control group (excluded from review) 
Animal studies or mechanical model studies (excluded from review) 
Extrapolations from existing data collected for other purposes, theoretical analyses (excluded from review) 
Rational conjecture (common sense); common practices accepted before evidence-based guidelines (excluded from review) 
LevelDefinition
RCTs or meta-analyses of multiple clinical trials with substantial treatment effects 
RCTs with smaller or less significant treatment effects 
Prospective, controlled, nonrandomized, cohort studies 
Historic, nonrandomized, cohort or case-control studies 
Case series: patients compiled in serial fashion, lacking a control group (excluded from review) 
Animal studies or mechanical model studies (excluded from review) 
Extrapolations from existing data collected for other purposes, theoretical analyses (excluded from review) 
Rational conjecture (common sense); common practices accepted before evidence-based guidelines (excluded from review) 
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