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Evidence-based medicine (EBM) provides a framework for informing the best possible practice. Simply, EBM aims to gather the best evidence gained from scientific investigation with the goal of optimizing medical decision making for the patients we treat. The impact of EBM is proportional to the quality and generalizability of the evidence at hand. The development of clinical practice guidelines has paralleled the growth and importance of the focus on medical quality. A discussion of the context in which practice guidelines have achieved their current prominence is followed by a presentation of their development, implementation, and maintenance. Finally, their quality and impact on medical practice are assessed.

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Evidence-based medicine gives the highest priority to the well-powered randomized controlled trial (RCT). The RCT is the most rigorous form of prospective scientific human experimentation to evaluate a therapeutic intervention (clinical trial) and has become the gold standard design. The RCT begins with an early stage with evaluation for safety and treating several doses (phase 1) and is followed by studies of surrogate markers of effectiveness (phase 2) and finally by definitive outcomes trials for safety and effectiveness (phase 3) (Table 13–1). It is now common to have phase 4 trials post-approval that afford the opportunity to expand the indications for a given therapy or to further explore safety concerns when events are rare but potentially fatal.2 The evidence can be best summarized by defining the patient population, the intervention, and the outcomes of interest.

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TABLE 13–1. Phases of FDA Trials
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Study Patients

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Inclusion/Exclusion Criteria

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The role of bias is a critical feature of what distinguishes clinical trials from clinical practice. The most important form of bias is selection bias whereby subjects enrolled in a trial differ systematically from those individuals in the general population. In EBM, this can lead to a trade-off between internal validity (findings can be applied to the types of patients enrolled in the trial) and external validity (generalizability to a wider population). By restricting the trial cohort to particular age or medical condition criteria, trial results can be skewed against those that are underrepresented. In an analysis of 283 RCTs published in high impact general medicine journals, 72% of patients were excluded on the basis of age and 39% were excluded due to being female.3 Not surprisingly, only 47% of exclusions were judged to be strongly justified. It is common to have less than 10% of screened patients enrolled and this is due in large part to ...

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