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Basic learning concepts in EBM: the bidimentional hierarchy of evidence
  1. Pierre La Rochelle
  1. Department of Medecine familiale et medecine d'urgence, Université Laval, CSSS de Kamouraska 360 des Érables, Sainte-Anne-de-la-Pocatière, Québec, Canada
  1. Correspondence to: Dr Pierre La Rochelle
    , Department of Medecine familiale et medecine d'urgence, Université Laval, CSSS de Kamouraska 360 des Érables, Sainte-Anne-de-la-Pocatière, Québec, Canada G0R 1Z0; pierre.la.rochelle{at}videortron.ca

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To introduce clinicians to EBM it can be useful to draw a simplified graph (figure 1) to get a basic understanding of some of the most important concepts. This graph focuses on the relationship between the study design and its corresponding risk of bias and the magnitude of an effect to observe. On the left, we have an upside-down triangle. The width level of the triangle depicts the prevalence of all the possible effects to be observed. In fact, small magnitude effects are very frequent whereas dramatic magnitude effects are very rare. Just to the right, a similar upright triangle portrays different types of studies ranked in accordance with their risk of bias. The width of the triangle represents the amplitude of the bias. Case reports are often inaccurate because they carry a very high …

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