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Most Published Research Findings May Be False

August 31, 2005
Public Library of Science
Published research findings are sometimes refuted by subsequent evidence, says Ioannidis in a paper published in the open access journal PLoS Medicine, with ensuing confusion and disappointment.

"There is increasing concern that in modern research, false findingsmay be the majority or even the vast majority of published researchclaims," says researcher John Ioannidis in an analysis in the openaccess international medical journal PLoS Medicine.

In his analysis, Ioannidis, of the University of Ioannina School ofMedicine, Greece, and Tufts University School of Medicine, UnitedStates, identifies the factors that he believes lead to researchfindings often being false.

One of these factors is that many research studies are small. "Thesmaller the studies conducted in a scientific field, the less likelythe 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 aperson's risk of disease, or how much a treatment is likely to improvea disease) are small.

Research findings are more likely true in scientific fields with largeeffects, such as the impact of smoking on cancer, than in scientificfields where postulated effects are small, such as genetic risk factorsfor diseases where many different genes are involved in causation. Ifthe effect sizes are very small in a particular field, says Ioannidis,it is "likely to be plagued by almost ubiquitous false positiveclaims."

Financial and other interests and prejudices can also lead to untrueresults. And "the hotter a scientific field (with more scientific teamsinvolved), the less likely the research findings are to be true," whichmay explain why we sometimes see "major excitement followed rapidly bysevere disappointments in fields that draw wide attention."

In their linked editorial, the PLoS Medicine editorsdiscuss the implications of Ioannidis' analysis. "Publication ofpreliminary findings, negative studies, confirmations, and refutationsis an essential part of getting closer to the truth," they say.

Nevertheless, the editors "encourage authors to discuss biases, studylimitations, and potential confounding factors. We acknowledge thatmost 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.

About PLoS Medicine

PLoS Medicine is an open access, freely available internationalmedical journal. It publishes original research that enhances ourunderstanding of human health and disease, together with commentary andanalysis of important global health issues. For more information, visit

About the Public Library of Science

The Public Libraryof Science (PLoS) is a non-profit organization of scientists andphysicians committed to making the world's scientific and medicalliterature a freely available public resource. For more information,visit<


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