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Evidence-based Medicine: Defining Evidence

The overall goals of evidence-based medicine (EBM) are to provide physicians and medical
personnel with the best information available in the field so that the clinical practices of these
professionals provide patients with the best possible care. 



The Philosophy of Evidence-based Medicine

Science and Medicine: Objectivity vs. Subjectivity

Medical Rhetoric as a Social and Communicational Construct

The Social and Rhetorical Implications of Medical Discourse

The Social and Rhetorical Implications of Defining Evidence



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The Social and Rhetorical Implications of Defining Evidence

Overall, the authors of Evidence-Based Medicine: How to Practice and Teach EBM make the following basic claim:  evidence should be empirical and based on research that follows the scientific method, so that from this, a set of information that is valid, accurate, relevant, and approaching absolute truth can be drawn from to practice effective medicine.  However, this claim is not explicitly addressed in the text and when criteria is provided, it varies throughout the book to adapt itself to particular situations.  For example, the criteria for validity varies from steps such as blind comparisons and an appropriate spectrum of patients which cross over between several sections to concerns such as length of patient follow-up or precision of treatment effect estimates that are more specific to individual situations (Sackett et al. 68, 95, 111).  To further question the claims found in the EBM text, the text incorporates (although only briefly addresses) using qualitative patient testimony and individual physicians’ assessments in clinical practice which is necessarily included in the clinical assessment, therefore incorporating those factors under the broad heading of evidence.  At the same time, the text also rejects that qualitative information as evidence because it does not meetthe standards of being objective and empirical, which apparently are determiners (albeit vague ones) of the status of information as evidence. 

The lack of explicit definition for the term evidence makes it possible to draw one of two conclusions: 1. The definition is so well delineated in common usage that the need to define it is a redundant study or 2. The definition is assumed to have a universal meaning, yet is still ambiguous enough to resist definition.  The first conclusion is unlikely since very few terms, if any, enjoy this elite status of being so ingrained in the language that clarification of meaning is not needed.  The second conclusion has potentially significant social repercussions such as miscommunication and unfounded persuasiveness.  If the term evidence is ambiguous, there is room for misinterpretation in the meaning of the communications using that term.  (Miscommunication has the potential to cause a range of effects from minor discrepancies to large-scale disasters.)   The lack of a specific definition also allows communicators to be persuasive without a solid argument by using “buzz-words” related to the general, commonly held ideas of evidence and the scientific method (e.g., validity, accuracy, relevancy, truth) that inspire confidence and a sense of authority within scientific and medical discourse communities.  Despite the fact that this authority is perhaps unfounded, these terms touch at the core of the scientific paradigms and therefore present a mask of reliability.  This initial persuasion may meet the superficial goals of EBM—encouraging medical practitioners to incorporate EBM into their daily clinical practice—but without a specific definition for evidence, the argument is not complete and the method remains partially ambiguous, reducing the clinical effectives of the method and defeating the ultimate purpose of the EBM movement—to increase the effectiveness of clinical practice and provide patients with the best possible care.

Written by Amanda Fullan, University of Wisconsin, Eau Claire
Last Updated December 15, 2001