Definition of Levels of Evidence (LoE) and Overall Strength of Evidence (SoE).

Abstract

Studies of therapy Level Risk of bias Study design Criteria I Low risk Study adheres to commonly held tenets of high quality design, execution and avoidance of bias Good quality RCT • Random sequence generation • Allocation concealment • Intent-to-treat analysis • Blind or independent assessment for important outcomes • Co-interventions applied equally • F/U rate of 80%+ • Adequate sample size II Moderately low risk Study has potential for some bias; study does not meet all criteria for level I, but deficiencies not likely to invalidate results or introduce significant bias Moderate or poor quality RCT Good quality cohort • Violation of one of the criteria for good quality RCT • Blind or independent assessment in a prospective study, or use of reliable data[a] in a retrospective study • Co-interventions applied equally • F/U rate of 80%+ • Adequate sample size • Controlling for possible confounding[b] III Moderately high risk Study has significant flaws in design and/or execution that increase potential for bias that may invalidate study results Moderate or poor quality cohort Case-control • Violation of any of the criteria for good quality cohort • Any case-control design IV High risk Study has significant potential for bias; lack of comparison group precludes direct assessment of important outcomes Case series • Any case series design a Outcome assessment is independent of healthcare personnel judgment. Reliable data are data such as mortality or re-operation. b Authors must provide a description of robust baseline characteristics, and control for those that are unequally distributed between treatment groups.