Evidence-based medicine in a nutshell. A guide to finding and using the best evidence in caring for patients.

Evidence-based medicine is the use of the best current evidence in making decisions about the care of individual patients. Practicing EBM requires recognition that in most encounters with patients, questions arise that should be answered to provide the patient with the best available medical care. Asking well-built clinical questions that contain 4 elements--a patient or problem, an intervention, a comparison intervention (if necessary), and an outcome--is an important step in practicing EMB. Once appropriate questions have been formulated, the best source for finding most types of best evidence is by searching the MEDLINE database by computer. MEDLINE searches have inherent software and operator limitations that make their reliability quite variable. One should be aware of these limitations and improve one's skills in searching. The Cochrane Collaboration Controlled Clinical Trials Registry contains more than 190,000 controlled clinical trials and is the best source of evidence about treatment. The quality (strength) of evidence is based on a hierarchy of evidence: results of systematic reviews of well-designed clinical studies, results of 1 or more well-designed clinical studies, results of large case series, expert opinion, and personal experience. Once the best evidence has been found, the EBM approach involves critically appraising the quality of the evidence, determining its magnitude and precision, and applying it to the specific patient. Guidelines to critically appraise and apply evidence are available. The clinical question, best evidence, and its critical appraisal should be saved in a format that can be easily retrieved for future use.