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Significance testing as perverse probabilistic reasoning

M Brandon Westover1*, Kenneth D Westover2 and Matt T Bianchi1

Author Affiliations

1 Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA

2 Harvard Radiation Oncology Program, Harvard Medical School, Boston, MA, USA

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BMC Medicine 2011, 9:20  doi:10.1186/1741-7015-9-20

Published: 28 February 2011


Truth claims in the medical literature rely heavily on statistical significance testing. Unfortunately, most physicians misunderstand the underlying probabilistic logic of significance tests and consequently often misinterpret their results. This near-universal misunderstanding is highlighted by means of a simple quiz which we administered to 246 physicians at two major academic hospitals, on which the proportion of incorrect responses exceeded 90%. A solid understanding of the fundamental concepts of probability theory is becoming essential to the rational interpretation of medical information. This essay provides a technically sound review of these concepts that is accessible to a medical audience. We also briefly review the debate in the cognitive sciences regarding physicians' aptitude for probabilistic inference.