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.
PLoS Medicine Editors
Public Library of Science
185 Berry Street, Suite 3100
San Francisco, CA 94107
PLEASE MENTION PLoS Medicine (www.plosmedicine.org) AS THE SOURCE FOR THESE ARTICLES. THANK YOU.
All works published in PLoS Medicine are open access. Everything is immediately available without cost to anyone, anywhere--to read, download, redistribute, include in databases, and otherwise use--subject only to the condition that the original authorship is properly attributed. Copyright is retained by the authors. The Public Library of Science uses the Creative Commons Attribution License.
About PLoS Medicine
PLoS Medicine is an open access, freely available international medical journal. It publishes original research that enhances our understanding of human health and disease, together with commentary and analysis of important global health issues. For more information, visit http://www.plosmedicine.org
About the Public Library of Science
The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org