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Centre for Evidence-
Based Medicine

How do we actually practice EBM?

The full-blown practice of EBM comprises 5 steps, and this book takes them up in turn:

Step 1
Converting the need for information (about prevention, diagnosis, prognosis, therapy, causation, etc) into an answerable question (Chapter 1).
Step 2
Tracking down the best evidence with which to answer that question (Chapter 2).
Step 3
Critically appraising that evidence for its validity (closeness to the truth), impact (size of the effect), and applicability (usefulness in our clinical practice) (the first halves of Chapters 3-7).
Step 4
Integrating the critical appraisal with our clinical expertise and with our patient's unique biology, values and circumstances (the second halves of Chapters 3-7).
Step 5
Evaluating our effectiveness and efficiency in executing Steps 1-4 and seeking ways to improve them both for next time (Chapter 9).

When we examine our practice and that of our colleagues and trainees in this 5-step fashion, we can identify 3 different "modes" or "styles" of practice. All of them involve the integration of evidence (from whatever source) with our patient's unique biology, values and circumstances of Step 4, but they vary in the execution of the other steps. For the conditions we encounter every day (e.g., unstable angina and venous thromboembolism) we need to be "up-to-the-minute" and very sure about what we are doing. Accordingly, we invest the time and effort necessary to carry out both steps 2 (searching) and 3 (critically appraising), and operate in the "appraising" mode; all the chapters in this book are relevant to the "appraising" mode.

For the conditions we encounter less often (e.g., temporal arteritis, aspirin poisoning), we conserve our time by seeking out critical appraisals already performed by others who describe (and stick to!) explicit criteria for deciding what evidence they selected and how they decided whether it was valid. That is, we leave out the time-consuming Step 3 (critically appraising) and carry out just Step 2 (searching) but restrict the latter to sources that have already undergone rigorous critical appraisal (Cochrane Reviews, Best Evidence, and the like1). Only the third portions ("Can I apply this valid, important evidence to my patient?") of Chapters 3-7 are strictly relevant here, and the growing database of pre-appraised resources is making this "searching" mode more and more feasible for busy clinicians. The reassuring thing about practicing in either the "appraising" or "searching" modes is that we can be pretty sure that we are providing "evidence-based care" to our patients.

This reassurance is lacking from the third mode of practice. For the problems we're likely to encounter very infrequently (the last example from the Sackett/Straus service was a man who developed bad pneumonia while trying to reject his heart-lung transplant), we "blindly" seek, accept and apply the recommendations we receive from authorities in the relevant branch of medicine. This "replicating" mode also characterizes the practice of medical students and clinical trainees when they haven't yet been granted independence and have to carry out the orders of their consultants. The trouble with the "replicating" mode is that it is "blind" to whether the advice received from the experts is authoritative (evidence-based, resulting from their operating in the "appraising" mode) or merely authoritarian (opinion-based, resulting from pride and prejudice). Sometimes we can gain clues about the validity of our expert source (Do they cite references?; Are they a member of the Cochrane Collaboration?) If we tracked the care we give when operating in the "replicating" mode into the literature and critically appraised it, we would find that some of it was effective, some useless, and some harmful. But in the "replicating" mode we'll never be sure which.


  1. A list of pre-appraised resources appears on page 4, and examples appear on the accompanying CD. This list can also be found on this website.