BackgroundEvidence-based medicine (EBM) has been propagated as a revolutionary development which will improve the quality of clinical decision-making and guideline development. Historically it follows an early 19th century French attempt to introduce mathematical analysis into clinical practice. This met with resistance from both clinicians and scientists and was only accepted in more recent times with the development of clinical epidemiology and clinical trials.Nature of EBMEMB claims to utilize the best available evidence to reach scientific conclusions, rejecting the appeal to expert authority. This involves a hierarchy of sources which places large controlled trials at the apex. Less value is attributed to arguments from clinical observation or pathophysiology. Systematic reviews and meta-anlyses of trials therefore provide the strongest evidence for clinical decisions.The concept of evidenceThe approach advocated in EBM is an over-simplification of the process of clinical thinking which involves interpretation and synthesis of relevant evidence from all sources and extrapolation to the clinical situation. In this process, there is no hierarchy of evidence. The relative value given to any particular evidence depends more upon its relevance and persuasiveness than the category to which it belongs. Discussion and debate amongst informed ‘experts’ is an integral feature of this process at each stage.Impact of EBMAlthough advocates of EBM acknowledge the contribution of all forms of evidence, the differential value attached to different sources has led to naïve and simplistic attempts to omit the traditional processes of interpretation, synthesis and extrapolation and to draw wide-ranging conclusions from trial data without adequate scientific discussion.