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Editor: J André Knottnerus
226 pp Price £30 ISBN 0-7279-1571-1 (p/b)
London: BMJ Books, 2002 .
Dr Knottnerus believes that, while ample attention has been given to the evidence basis for therapeutics, formal evaluation of diagnostic methods has been unjustly neglected. With The Evidence Base of Clinical Diagnosis he aims to help not only researchers but also clinicians and students who wish to get a grip on the scientific principles. One would be hard pushed to imagine a better example of globalization than this book, published by the BMJ in London with authors drawn from the Netherlands, the USA and Australia, type set in India and printed in Spain.
Contributors discuss the objectives of diagnostic testing and the challenges of designing studies to evaluate these procedures. The various options are dealt with in detail—for example, the cross-sectional study, the randomized controlled trial, and the before-and-after study as well as the systematic review—with a warning that results cannot always be extrapolated from one environment to another, such as hospital to primary care. The reader is offered formulas for calculating sensitivity, specificity, likelihood ratios and other indices that will aid analysis. A chapter on computer-aided diagnosis adopts a general approach, and I would have liked more examples of how computers can change clinical practice (if they do). Of particular interest to me was a discussion of the psychological and cognitive processes involved in clinical reasoning; it offers practical tips on how an experienced clinician can impart personal strategies to students and junior doctors. I was less happy with the contributions on how to improve test-ordering, because they start from the assumption that a great many diagnostic tests are unneccesary and are requested for no clear reason. The discussion focuses, rather predictably and one-sidedly, on the use of medical education, guidelines and other doctor-oriented interventions to reduce test-ordering. The changes that have taken place in society—in terms of patient expectations and the ever more demanding litigation culture—are not really explored. One weakness of the whole book is a failure to examine the issue of diagnostic tests from the patient's viewpoint, and in particular the reassurance value that patients gain from a negative test result. And, not least, there are the vital medicolegal implications of having done or not done a diagnostic investigation.
My personal reservations about the book stem partly from its global origins. In many developed health system it may well be true that diagnostic tests are being over-ordered. I need to be persuaded that this applies to the British National Health Service, which has suffered rather from a lack of diagnostic facilities. Nevertheless, this well-written text will be useful to its target audience.