Evidence-based medicine originated at McMaster University, Hamilton, Ontario, Canada, where it was defined as "the integration of current best evidence with clinical expertise and patient values" by the Evidence-based Medicine Working Group led by Drs Gordon Guyatt and David Sackett. From this developed the McMaster University and National Health Service Centre for Evidence-Based Medicine, University of Oxford, paradigm of evidence-based practice, which consists of five steps that can be used by ordinary practitioners: formulate answerable questions with which to search for evidence, search the literature, appraise the retrieved evidence by using explicit methods, apply results to a patient or patient group, and evaluate one's evidence-based practice and clinical performance and practice. This communication is about the first two steps of this process. Step 1 provides a framework for more effective question formulation that improves subsequent literature searches. It works equally well for questions about diagnostic and interventional radiology. A clinical scenario for a diagnostic question is used to illustrate the formulation of an answerable question. This question is then used to illustrate step 2-how and where to search for evidence.
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