Other factors also contribute to the challenge. For example, researchers in neuroscience and psychological science may not understand how statistical analyses for fMRI differ from those in behavioral studies, and so may not accurately evaluate the statistical power of their fMRI analyses, Turner said.
"They may confuse the high retest accuracy of fMRI with high replicability," he said. "But that sort of accuracy refers only to retests of the same individuals engaged in the same tasks, not to similarity across separate small groups."
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To overcome the problem of expense, Miller suggests that researchers pool their resources to conduct fMRI studies across numerous sites involving greater numbers of participants. This would likely result in more diverse participant pools. It also would advance the work of many scientists, laboratories and institutions at once, yielding more data per participant with potentially greater impact.
"Replicability is the foundation of scientific progress," the authors wrote. "Unfortunately, for a variety of reasons, many scientific fields are gripped by a crisis of irreproducibility. While some of the causes of the crisis are deeply woven into the academic landscape - incentives related to publication, funding and tenure - the most straightforward solution relates to statistical power."
"Our study points to a major problem in the field of cognitive neuroscience, a field in which fMRI studies are a commonly used tool," Barbey said. "But this is a problem that we can solve by increasing the size of the samples we study."
Barbey is a professor in the Beckman Institute for Advanced Science and Technology and an affiliate of the Carl R. Woese Institute for Genomic Biology at the U. of I. He directs the Center for Brain Plasticity, a partnership between the Beckman Institute and the Interdisciplinary Health Sciences Institute at Illinois.
This research is based upon work supported by the Office of the Director of National Intelligence, Intelligence Advanced Research Projects Activity.
Editor's notes:
The paper "Small sample sizes reduce the replicability of task-based fMRI studies" is available from the U. of I. News Bureau. DOI: 10.1038/s42003-018-0073-z
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