Preface

Evidence-based medicine (EBM)—as a concept with that particular moniker—is now almost 25 years old. Looking back, periods of infancy, childhood, adolescence,¹ and now a mature adulthood are evident.² This third edition of the Users' Guides to the Medical Literature firmly establishes the maturity of the EBM movement.

The first articulation of the world view that was to become EBM appeared in 1981 when a group of clinical epidemiologists at McMaster University, led by David Sackett, MD, published the first of a series of articles that advised clinicians on how to read clinical journals.³ Although a huge step forward, the series had its limitations. After teaching what they then called critical appraisal for a number of years, the group became increasingly aware of both the necessity and the challenges of going beyond reading the literature in a browsing mode and instead using research studies to solve patient management problems on a day-to-day basis.

In 1990, I assumed the position of residency director of the Internal Medicine Program at McMaster. Through Dave Sackett's leadership, critical appraisal had evolved into a philosophy of medical practice based on knowledge and understanding of the medical literature supporting each clinical decision. We believed that this represented a fundamentally different style of practice and required a term that would capture this difference.

My mission as residency director was to train physicians who would practice this new approach to medicine. In the spring of 1990, I presented our plans for changing the program to the members of the Department of Medicine, many of whom were unsympathetic. The term suggested to describe the new approach was scientific medicine. Those already hostile were incensed at the implication that they had previously been “unscientific.” My second try at a name for our philosophy of medical practice, evidence-based medicine, became extremely popular in a very short time. To use the current vernacular, it went viral.⁴

After that fateful Department of Medicine meeting at McMaster, the term EBM first appeared in the autumn of 1990 in an information document for residents entering, or considering application to, the residency program. The relevant passage follows:

Residents are taught to develop an attitude of “enlightened scepticism” towards the application of diagnostic, therapeutic, and prognostic technologies in their day-to-day management of patients. This approach … has been called “evidence-based medicine.” … The goal is to be aware of the evidence on which one's practice is based, the soundness of the evidence, and the strength of inference the evidence permits. The strategy employed requires a clear delineation of the relevant question(s); a thorough search of the literature relating to the questions; a critical appraisal of the evidence and its applicability to the clinical situation; a balanced application of the conclusions to the clinical problem.

The first published appearance of the term was in the American College of Physicians' Journal Club in 1991.⁵ Meanwhile, our group of enthusiastic evidence-based medical educators at McMaster were refining our practice and teaching of EBM. Believing that we were on to something important, we linked up with a larger group of academic physicians, largely from the United States, to form the first Evidence-Based Medicine Working Group and published an article in JAMA that defined and expanded on the description of EBM, labeling it as a “paradigm shift.”⁶

This working group then addressed the task of producing a new set of articles, the successor to the Readers' Guides, to present a more practical approach to applying the medical literature to clinical practice. With the unflagging support and wise counsel of JAMA Deputy Editor Drummond Rennie, MD, the Evidence-Based Medicine Working Group created a 25-part series called the Users' Guides to the Medical Literature, published in JAMA between 1993 and 2000.⁷ The series continues to be published in JAMA, with articles that address new concepts and applications.

The first edition of the Users' Guides to the Medical Literature was a direct descendant of the JAMA series. By the time of the book's publication in 2002, EBM had already undergone its first fundamental evolution, the realization that evidence was never sufficient for clinical decision making. Rather, management decisions always involve trade-offs between desirable and undesirable consequences and thus require value and preference judgments. Indeed, in the first edition of the Users' Guide to the Medical Literature, the first principle of EBM was presented as Clinical Decision Making: Evidence Is Never Enough, joining the previously articulated principle of a hierarchy of evidence.

It did not take long for people to realize that the principles of EBM were equally applicable for other health care workers, including nurses, dentists, orthodontists, physiotherapists, occupational therapists, chiropractors, and podiatrists. Thus, terms such as evidence-based health care and evidence-based practice are appropriate to cover the full range of clinical applications of the evidence-based approach to patient care. Because our Users' Guides are directed primarily at physicians, we have continued with the term EBM.

The second edition incorporated 2 new EBM developments in EBM thinking. First, we had realized that only a few clinicians would become skilled at critically appraising original journal articles and that preappraised evidence would be crucial for evidence-based clinical practice. Second, our knowledge of how best to ensure that clinical decisions were consistent with patient values and preferences was rudimentary and would require extensive study.

This third edition of the Users' Guides to the Medical Literature builds on these realizations, most substantially in the revised guide to finding the evidence. The emphasis is now on preappraised resources and particularly on the successor to medical texts: electronic publications that produce updated evidence summaries as the data appear and provide evidence-based recommendations for practice.

Awareness of the importance of preappraised evidence and evidence-based recommendations is reflected in other changes in the third edition. We have added a fundamental principle to the hierarchy of evidence and the necessity for value and preference judgments: that optimal clinical decision making requires systematic summaries of the best available evidence.

This principle has led to a fundamental revision of the Users' Guide to systematic reviews, which now explicitly includes the meta-analyses and acknowledges 2 core considerations. The first is how well the systematic review and meta-analysis were conducted. The second, inspired by the contributions of the GRADE (Grading of Recommendations Assessment, Development and Evaluation) Working Group,⁸ demands an assessment of the confidence that one can place in the estimates of effect emerging from the review and meta-analysis. However well done the review, if the primary evidence on which it is based warrants little confidence, inferences from the review will inevitably be very limited.

The third edition of the Users' Guides to the Medical Literature incorporates the lessons we have learned in more than 20 years of teaching the concepts of EBM to students with a wide variety of backgrounds, prior preparation, clinical interest, and geographic location. Indeed, among our many blessings is the opportunity to travel the world, helping to teach at EBM workshops. Participating in workshops in Thailand, Saudi Arabia, Egypt, Pakistan, Oman, Kuwait, Singapore, the Philippines, Japan, India, Peru, Chile, Brazil, Germany, Spain, France, Belgium, Norway, the United States, Canada, and Switzerland—the list goes on—provides us with an opportunity to try out and refine our teaching approaches with students who have a tremendous heterogeneity of backgrounds and perspectives. At each of these workshops, the local EBM teachers share their own experiences, struggles, accomplishments, and EBM teaching tips that we can add to our repertoire.

We are grateful for the extraordinary privilege of sharing, in the form of the third edition of Users' Guides to the Medical Literature, what we have learned.

Gordon Guyatt, MD, MSc

McMaster University

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