All opinions are not equal.

To the Editor: Gibbons et al1 detail the “noble” and Herculean task of developing American College of Cardiology/American Heart Association cardiovascular guidelines. Recommendations are based on either experimental results or opinion, with the latter being considered of uniformly lower evidentiary importance. The contribution of opinion to the guidelines is substantial in that opinion supports more than half of the current recommendations and appears to contribute continuity and cohesiveness to recommendations that would otherwise be fragmented in large part as a result of insufficient experimental data. On closer reading, it becomes apparent that the treatment of all nonexperimental support as “opinion” masks at least 2 different, distinct, and incommensurable, types of opinion evidence. A low level of evidentiary importance may be quite appropriate for the many opinions that deal with issues that are open to experimental testing when this testing has not been done for a variety of reasons ranging from a lack of interest in funding to ethical issues regarding controls. However, other assignments of opinion to level C evidence ignores that our search for scientific truth takes places within a framework of other truths and assumptions. For example, the need for a clinical history and tests that are intrinsic to the definition of disease states often is not an opinion that is subject to scientific testing but rather is a presupposition of our scientific testing. Moreover, our work proceeds within moral and legal constraints. Moral imperatives, such as “Do no harm,” form the basic fabric of our profession and have predated and will outlive much of our current experimental truths. Opinion evidence often reflects moral imperatives, including not treating when there is no indication, when there is a significant contraindication, when risk outweighs benefit, when the patient refuses treatment, or when treatment cannot be effective. Moreover, no matter how therapeutically efficacious an illicit drug is, it must receive a class III not a class I recommendation. These types of truths and assumptions are arguably of equal weight to level A or B evidence. Hence, in important respects, the current hierarchy of evidence blurs scientific assumptions that could plausibly be subject to testing, with other truths that are not, and cannot be, evidence-based. It is a logical error to group these distinct types of “opinions” as one and assign them the same level of evidentiary import.