Clinical practice based on personal experience, prejudice, and the opinion of authorities may be filled with dogma, misunderstanding, and unverified belief. Clinical studies of inappropriate design, in which biases from various sources result in wrong conclusions, may mislead clinicians. Evidence-based medicine is the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research. Because the randomized controlled trial is more likely to inform us and less likely to mislead us, it has become the gold standard for judging whether a treatment does more good than harm. When designing a clinical trial, we can, in turn, utilize the knowledge of clinical epidemiology, which provides theoretical background to evidence- based medicine; for example, techniques that minimize systematic biases have been successfully developed. Discussing the study design of the Japan EC-IC bypass trial (JET study), we illustrated how to design clinical trials to generate the best evidence in light of clinical epidemiology.
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