Guidelines are a constructive response to the reality that the practicing physician requires assistance to assimilate and apply the exponentially expanding, often contradictory, body of medical knowledge. Guidelines are widely perceived as evidence based, not authority based, and therefore as unbiased and valid. Because they are sponsored by organizations, staffed by experts, and conducted according to apparently formal processes, the products of the exercise—the guidelines—are generally assumed to have the same level of certainty and security as conclusions generated by the conventional scientific method. For many clinicians, guidelines have become the final arbiters of care.