Almost one-third of large medical studies published in three "influential" journals between 1990 and 2003 were later contradicted or found to overstate results, according to a report published on Wednesday in the... Journal of the American Medical Association, the AP/Las Vegas Sun reports. For the report, John Ioannidis, a researcher at the University of Ioannina in Greece, reviewed a number of large studies published in the New England Journal of Medicine, the Lancet and JAMA -- 45 of which involved claims about the effectiveness of a medication or treatment. According to the report, later research contradicted the results of seven, or 16%, of the studies and found that an additional seven studies, or 16%, overstated results. The report found the subsequent research in those 14 cases -- which included studies contradicting the original findings that hormone replacement therapy protected menopausal women from heart disease, that nitric oxide improved survival rates for patients with respiratory failure and that antibody treatment improved survival rates for some sepsis patients -- involved larger numbers of participants or had improved designs. Ioannidis said, "Contradicted and potentially exaggerated findings are not uncommon in the most visible and most influential original clinical research." However, Ioannidis added, "There's no proof that the subsequent studies ... were necessarily correct." NEJM editors said in a statement that accompanied the report, "A single study is not the final word, and that is an important message." JAMA Editor in Chief Catherine DeAngelis added that the media can contribute to the problem with misleading headlines that overstate the results of studies (Tanner, AP/Las Vegas Sun, 7/12).

An abstract of the study is available online.

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