Since the time of ancient Greece, medicine has been based on evidence. Conscientious physicians have always familiarized themselves with recent research and made their best efforts to keep abreast of journals. The modern term, evidence-based medicine (EBM), however, describes the effort to link both clinical practice and public policy to evidence that interventions improve outcomes of significance. Several aspects of this definition warrant attention.

First, the focus is on interventions. A large proportion of biomedical research concerns basic science and technology. Only some of this research investigates whether interventions in clinical practice or public policy improve health. Evidence-based medicine asks whether such interventions improve outcomes. Second, the emphasis is on outcomes of significance, those that patients and the public consider important. Intermediate outcomes and surrogate endpoints, such as pathophysiologic changes (as defined later), receive less weight. Third, EBM seeks to document the quality of the evidence for interventions and to make explicit the extent to which clinical practices and public policies are based on data or opinion. It is a misconception that EBM advocates withholding treatments for which evidence is lacking.<sup>69 Sackett D.L., Rosenberg W.M., Gray J.A. , e al. Evidence-based medicine: What it is and what it is not BMJ J 1996 ;  312 : 71

Cliccare qui per andare alla sezione Riferimenti</sup> Rather, it emphasizes the importance of disclosing the lack of evidence, to inform professionals and the public and to prioritize research better.

Current interest in EBM grew out of the nascent health care crisis of the late 1980s.<sup>23 Ellwood P.M. Outcomes management: A technology of patient experience N Engl J Med 1988 ;  318 : 1549  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> Rising costs of care and increasing evidence of disturbing variations in clinical practice<sup>11 Chassin M.R., Kosecoff J., Park R.E. , e al. Does inappropriate use explain geographic variations in the use of health care services? A study of three procedures JAMA 1987 ;  258 : 2533

Cliccare qui per andare alla sezione Riferimenti</sup> raised questions about the effectiveness and appropriateness of many tests and treatments.<sup>80 Woolf S.H. Practice guidelines: A new reality in medicine. I. Recent developments Arch Intern Med 1990 ;  150 : 1811

Cliccare qui per andare alla sezione Riferimenti</sup> This concern gave rise to new government agencies and research initiatives, <sup>66 Roper W.L., Winkenwerder W., Hackbarth G.M. , e al. Effectiveness in health care: An initiative to evaluate and improve medical practice N Engl J Med 1988 ;  319 : 1197  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> closer attention to evidence by private insurers and health plans, <sup>12 Chassin M.R., Galvin R.W., for the National Roundtable on Health Care Quality The urgent need to improve health care quality: Institute of Medicine National Roundtable on Health Care Quality JAMA 1998 ;  280 : 1000  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> and a new domain of scholarly research that focuses on systematic reviews and meta-analyses (e.g., EBM journals and theme sections in journals, <sup>25 Evidence-Based Medicine Working Group Evidence-based medicine: A new approach to teaching the practice of medicine JAMA 1992 ;  268 : 2420

Cliccare qui per andare alla sezione Riferimenti, 32 Geyman J.P. POEMs as a paradigm shift in teaching, learning, and clinical practice J Fam Pract 1999 ;  48 : 343

Cliccare qui per andare alla sezione Riferimenti, 59 Mulrow C.D., Cook D.J., Davidoff F. Systematic reviews: Critical links in the great chain of evidence Ann Intern Med 1997 ;  126 : 389

Cliccare qui per andare alla sezione Riferimenti</sup> Cochrane Library<sup>6 Bero L., Rennie D. The Cochrane Collaboration: Preparing, maintaining, and disseminating systematic reviews of the effects of health care JAMA 1995 ;  274 : 1935

Cliccare qui per andare alla sezione Riferimenti</sup>). It promulgated a new approach to practice guidelines that emphasized a direct linkage between recommendations and evidence, making explicit disclosures when evidence was lacking, and giving lesser weight to opinion-based policies.<sup>22 Eddy D.M. Clinical Decision Making: From Theory to Practice   A Collection of Essays from JAMA Boston: Jones and Bartlett (1995). 

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The limitations and potential hazards of EBM are discussed later. Most of this article focuses on the two core elements of EBM: (1) reviewing evidence and (2) developing policy based on such reviews. Common to almost all EBM efforts is the task of gathering and evaluating relevant evidence from published (and sometimes from unpublished) literature. This comprehensive summary and critical appraisal of evidence, termed a systematic review, <sup>14 Cook D.J., Mulrow C.D., Haynes R.B. Systematic reviews: Synthesis of best evidence for clinical decisions Ann Intern Med 1997 ;  126 : 376

Cliccare qui per andare alla sezione Riferimenti</sup> characterizes the quality of the evidence but often stops short of making recommendations. Evidence-based practice guidelines and other quality improvement tools take the additional step of setting policy for patient care or public policy based on the systematic review. Each of these processes is discussed in this article.