What are the classes and levels of evidence used in AHA/ASA recommendations?
The American Heart Association/American Stroke Association (AHA/ASA) provide guidelines for the treatment and prevention of stroke, and these guidelines are divided into classes and levels of evidence. The classes are defined as follows: Class I – Conditions for which there is evidence for and/or general agreement that the procedure or treatment is useful and effective; Class II – Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment; Class IIa – The weight of evidence or opinion is in favor of the procedure or treatment; Class IIb – Usefulness/efficacy is less well established by evidence or opinion; Class III – Conditions for which there is evidence and/or general agreement that the procedure or treatment is not useful/effective and in some cases may be harmful.