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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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Medical Rhetoric as a Social and Communicational Construct

Building on the idea that medicine is not entirely objective, and may even be entirely subjective if we subscribe to Brummett’s theories on the nature of observation, the question of how the discourse of the medical community shapes the information that it is communicating comes to the surface. 

First, one must look at what a definition is and how it comes to be.  Ed Schiappa explains this effectively when he says, “standard definitions represent temporary agreements of an audience as to how particular words are to be used” (404).  In other words, definitions are simply a temporary social agreement, a consensus within a discourse community at a given time, forever changing and taking on new connotations as the discourse community adapts terms to fit new ideas and information.  Most often these definitions are implied and contextual, not spelled out in any given discursive text: such is the case with the EBM training manual.  

 David Sackett and his fellow authors did try to define evidence indirectly, even though the result was vague and frequently raised more questions than it answered.  Sackett et al. state, “New evidence from clinical research both invalidates previously accepted diagnostic tests and treatments and replaces them with new ones that are more powerful, more accurate, more efficacious, and safer” (1).  This sentence represents ideas that are found throughout the text, particularly the idea that, in general, newer is better.  The text continually emphasizes the need for “current best evidence,” suggesting and sometimes outright stating that older evidence is not as desirable even though it may be more thoroughly tested.  Sackett et al. even go so far as to suggest that old textbooks be burned, although they amend this statement by saying that if these textbooks were “revised frequently (at least once a year),…heavily referenced, at least for declarations about diagnosis and management,…[and] selected according to explicit principles of evidence” (Sackett et al. 30, 31), then their fragile pages could escape the incinerator.  The first two criteria are fairly straightforward, the first gives a time line and the second is simple enough, but the “explicit principles of evidence” are never provided and remain a mystery.  A direct definition of evidence is once again not provided even when the text appears to be begging for that very information.  In Sackett et al.’s listing of qualities that are desired when searching for evidence, “more accurate” refers back to the idea of absolute truth, again suggesting that evidence should have a high level of validity which these authors parenthetically defined as “closeness to the truth” (Sackett et al. 1,4) once again demonstrating how the theoretical assumptions within the field of science are so pervasive that scientists are seldom even aware that they are being used, much less that they can be questioned. 

These claims regarding the values and ideas of truth and validity all serve one overall purpose in the text Evidence-Based Medicine: How to Practice and Teach EBM: to persuade medical professionals to practice medicine in the manner that the promoters of EBM believe to be the most effective.  This purpose has numerous social implications that can be examined through the theories of social scientist Jurgen Habermas.  Habermas presents the idea that people go through a process of “communicative action” in which they communicate for the purpose of convincing someone else to act because he/she has come to agree with the concept being communicated (Cooke 8, 9).  This then translates into the idea that individual claims are made for specific purposes and that “claims to validity are raised in actual historical contexts which do not remain stationary, but are subject to change...[and that] no one can predict whether changes in context will have an effect on what is accepted here and now as sufficient justification in support of the validity of a given claim” (Cooke 2).  When applied to EBM, these theories show that the definitions of evidence must be considered contextually, keeping in mind the ultimately persuasive goal of the text, since its purpose is to enable medical practitioners to practice EBM while justifying the practice of EBM at the same time. 

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