In his analysis, Ioannidis, of the University of Ioannina School of Medicine, Greece, and Tufts University School of Medicine, United States, identifies the factors that he believes lead to research findings often being false.
One of these factors is that many research studies are small. "The smaller the studies conducted in a scientific field, the less likely the research findings are to be true," says Ioannidis.
Another problem is that in many scientific fields, the "effect sizes" (a measure of how much a risk factor such as smoking increases a person's risk of disease, or how much a treatment is likely to improve a disease) are small.
Research findings are more likely true in scientific fields with large effects, such as the impact of smoking on cancer, than in scientific fields where postulated effects are small, such as genetic risk factors for diseases where many different genes are involved in causation. If the effect sizes are very small in a particular field, says Ioannidis, it is "likely to be plagued by almost ubiquitous false positive claims."
Financial and other interests and prejudices can also lead to untrue results. And "the hotter a scientific field (with more scientific teams involved), the less likely the research findings are to be true," which may explain why we sometimes see "major excitement followed rapidly by severe disappointments in fields that draw wide attention."
In their linked editorial, the PLoS Medicine editors discuss the implications of Ioannidis' analysis. "Publication of preliminary findings, negative studies, confirmations, and refutations is an essential part of getting closer to the truth," they say.
Nevertheless, the editors "encourage authors to discuss biases, study limitations, and potential confounding factors. We acknowledge that most studies published should be viewed as hypothesis-generating, rather than conclusive."
Citation: Ioannidis JPA (2005) Why most published research findings are false. PLoS Med 2(8): e124.
John P.A. Ioannidis
University of Ioannina, School of Medicine, Ioannina, Greece
Tufts University, School of Medicine, Boston, Massachusetts, U.S.A.
THE RELATED ARTICLE FROM PLoS Medicine:
Citation: PLoS Medicine Editors (2005) Minimizing mistakes and embracing uncertainty. PLoS Med 2(8): e272.
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