The use of evidence in medicine is certainly not new. Scientific medicine, by its very nature, implies both theory and practice that flow from objective, verifiable, shared data—the "evidence." What has changed in clinical medicine in recent decades is the very nature of clinical evidence itself, in three important ways: the standards for gathering it, the tools for analyzing it, and the social context in which it is used.

Time was, not so long ago, when the standard unit of clinical information was the individual patient, captured in the detail of the case report, often elegantly and precisely at that. But increasing realization of the power of probabilistic reasoning has now shifted us from an older anecdotal to a new epidemiologic standard [1], thus "raising the bar" for the acceptable level of etiologic and diagnostic evidence. On the therapeutic side, case reports have yielded to population-derived studies, of which the randomized controlled trial is the prototype or "gold standard" of therapeutic evidence.

Time was, not so long ago, when the tool kit for assembling and interpreting clinical evidence consisted largely of some rather basic biostatistics. The array of tools in the kit is now greatly expanded, including the many sophisticated concepts and techniques of experimental trial design, decision analysis, and clinical epidemiology. Particularly important among these is the concept that a single study, although it may provide the truth, is often not enough. The whole truth may require a synthesis of the evidence from all the best studies, optimally through the use of meta-analysis [2].

And time was when expert opinion—authority—carried as much weight as the clinical scientific record, and often more. The experience of experts still counts for something in medicine, and the social nexus of medical thought still has an "autocratic" or "authoritarian" cast to it, perhaps as part of the human response to the inherent uncertainties of clinical medicine [3, 4]. But practicing physicians increasingly expect, and are expected, to base their decisions on "the evidence" rather than on authority; at the same time, the wide availability of strong clinical evidence supports the increasing democratization of medical decision-making power [5]. "Authoritarian medicine" may thus be gradually yielding ground to "authoritative medicine."

These changes are reflected in the concept of evidence-based medicine, which was introduced several years ago [6]. They have already led to various new approaches to assembling, judging, and presenting medical information [7, 8].

Evidence-Based Medicine will continue the tradition established by its "sister" publication, ACP Journal Club, scouring the literature from more than 50 journals in all major clinical specialties for key articles that meet certain criteria for scientific merit and clinical relevance, then abstracting and concisely commenting on them. Its arrival will be most welcome because it will extend the reach of the concept within medicine and throughout the world.