Grade of Recommendation  Strength of Evidence 
A Strong evidence  A preponderance of level I and or level II studies support the recommendation. This must include at least 1 level 1 study 
B Moderate evidence   A single high-quality randomized controlled trial or a preponderance of level II studies support the recommendation  
C Weak evidence  A single level II study or a preponderance of level III and IV studies, including statements of consensus by content experts, support the recommendation  
D Conflicting evidence  Higher-quality studies conducted on this topic disagree with respect to their conclusions. The recommendation is based on these conflicting studies  
E Theoretical/foundational evidence  A preponderance of evidence from animal or cadaver studies, from conceptual models/ principles, or from basic science/bench research support this conclusion  
F Expert opinion  Best practice based on the clinical experience of the guidelines development team