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Principles of Evidence-Based Medicine and Quality of Evidence



The March 1, 1981 issue of the Canadian Medical Association Journal included a landmark article titled “How to read clinical journals: I. Why to read them and how to start reading them critically.” Written by David Sackett, MD (1934–2015) of McMaster University, it introduced a series of articles that highlighted the importance of critical appraisal of the literature. Starting in 1993, a set of articles in the Journal of the American Medical Association titled “Users’ guides to the medical literature” reprised and expanded on the earlier series. These works, and other efforts by their authors, made critical appraisal of the literature accessible to the masses and laid the groundwork for evidence-based medicine (EBM).

Gordon Guyatt, MD, coined the term “evidence-based medicine” in the early 1990s, while he served as the internal medicine residency program director at McMaster University. Dr. Guyatt and colleagues had incorporated critical appraisal of the literature into the residency program curriculum, and Dr. Guyatt wanted a term to describe and advertise their efforts.

EBM caught on quickly over subsequent years as practicing physicians and training programs embraced and taught its methods, with dissemination greatly fueled by the rise of the Internet.


An early criticism of EBM, which some still harbor, was that it did not properly acknowledge the importance of clinical judgment or patient preferences. In an updated framework for evidence-based practice by R. Brian Haynes, P.J. Devereaux, and Gordon Guyatt in 2002, evidence-based decisions are based on four cardinal elements: (1) the research evidence, (2) the patient’s clinical state and circumstances, (3) the patient’s preferences, and (4) the clinician’s judgment and expertise.


  • Clinical judgment and expertise are essential to the practice of EBM. These skills facilitate optimal decision making by allowing the clinician to properly weigh the research evidence in the context of the patient’s individual clinical circumstances and preferences. Decisions should never be based on the evidence alone.

Practicing EBM may appear to be a straightforward affair with its methodical approaches to clinical question construction and to searching and critically appraising the literature. However, hospitalists should not confuse process with content, and they will often find that EBM tends to highlight clinical uncertainty and gaps in the medical literature. High-quality evidence does not exist to guide all clinical decisions, and extrapolation from lower quality evidence is often necessary. Bayesian diagnostic decision making often relies on clinical judgment to formulate pretest probabilities or to deal with the uncertainty that accompanies inconclusive post-test probabilities. Learning to deal with uncertainty is a core competency of EBM, which draws heavily on clinical judgment and experience.


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