As many as one-third of previously published randomized clinical trials could be re-analyzed in ways that modify the conclusions of how many or what types of patients need to be treated, according to a new study by researchers at the Stanford University School of Medicine. A culture that fails to encourage data sharing makes such re-analysis of the data extremely rare, the researchers said. They were able to identify only 37 published re-analyses over more than three decades of research. Of these, only five were conducted by researchers who were not associated with the original studies.

The new study will be published Sept. 9 in the Journal of the American Medical Association.

"There is a real need for researchers to provide access to their raw data for others to analyze," said John Ioannidis, MD, DSc, professor of medicine and director of the Stanford Prevention Research Center. "Without this access, and possibly incentives to perform this work, there is increasing lack of trust in whether the results of published, randomized trials are credible and can be taken at face value. The recent hot debates about whether oseltamivir works are only the tip of the iceberg in this crisis of confidence."

Oseltamivir is an antiviral medication marketed under the trade name Tamiflu. Although it is licensed to treat influenza A and influenza B, some subsequent analyses and trials conducted after the drug was approved have suggested that its benefits do not outweigh the risks of side effects in otherwise healthy adults.

Ioannidis is the senior author of the study. Postdoctoral scholar Shanil Ebrahim, PhD, is the lead author. Ioannidis is co-director of the recently launched Meta-Research Innovation Center at Stanford, or METRICS, which aims to advance excellence in scientific research by evaluating and optimizing scientific practices. Enhancing reproducibility and data sharing could be instrumental in this regard.

Ebrahim and his colleagues used the MEDLINE database to conduct their study. MEDLINE is a bibliographic database maintained by the National Library of Medicine. It contains over 25 million citations of biomedical publications from roughly 5,600 journals worldwide. They searched for articles written in English describing the re-analysis of raw data used in previously published studies. Meta-analyses were excluded from the study, as were studies testing a different hypothesis than the original trial.