Definitions of strength of evidence grade
A=Multiple well designed randomized clinical trials, directly relevant to the recommendation, yield a consistent pattern of findings.
B=Some evidence from randomized clinical trials supported the recommendation, but the scientific support was not optimal. For instance, either few randomized trials existed, the trails that did exist were somewhat inconsistent, or the trails were not directly relevant to the recommendation.
C=Reserved for important clinical situations where the panel achieved consensus on the Recommendation in the absence of relevant randomized controlled trials.