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Strength of Evidence
A Directly based on category I evidence that is well designed
B Directly based on category II evidence or recommendation from category I
evidence that is not well designed
C Directly based on category III evidence or recommendation from category II
evidence that is not well designed
D Directly based on category IV or recommendation from category III evidence
that is not well designed
LB Laboratory based
NR Not Rated
Category of Evidence
Ia Evidence from meta-analysis of randomized controlled trials
Ib Evidence from at least one randomized controlled trial
Ic Evidence from at least 1 randomized controlled trial that was not very well
designed
IIa Evidence from at least one controlled study without randomization
IIb Evidence from at least one other type of quasi-experimental study
IIc Evidence from one of the above that was not very well designed
IIIa Evidence from well-designed nonexperimental descriptive studies, such as
comparative studies
IIIb Evidence from nonexperimental descriptive studies, such as comparative studies,
that were not very well designed
IVa Evidence from expert committee reports and/or opinions or clinical experience
of respected authorities