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Table 2 Advantages and disadvantages of sources of unpublished data described by interview respondents

From: Strategies for obtaining unpublished drug trial data: a qualitative interview study

Sources of unpublished data Advantages Disadvantages
Study authors They have the data • Not always responsive
• Want to keep the data to themselves for their own publications
Drug companies • Have complete clinical study reports • Rarely responsive
• Want to know what you want to do with the data
Regulatory agencies • Includes summary data from clinical trials • Not a user friendly interface
• People do not know what information/data are available on the agencies websites
• Not as much information about older drugs
• Data on phase 4 studies often missing
Grey literature Provide information about studies that may be published, for example, presented at conferences. • Does not provide key pieces of outcome data
• Rarely peer reviewed
Law firms - class action suits in the US • Can uncover all of the data for a given drug • Happens for few drugs
• Tens of thousands of pages of documents to search
• Judges must agree to release the data
Grant organizations • Provide a list of all studies they sponsor • Sponsor a small number of studies
Marketing materials from companies and financial reviews • More or different data may appear in financial publications compared to the scientific literature • Can suggest that unpublished data exist, but the data must still be obtained
The media – journalists, press officers • Companies will respond to media pressure • Data may not be complete
Clinical trial registries • Provide awareness of all of the trials being conducted on a certain drug in a certain area • Results data are generally not available
   • Some registries do not contain registration of Phase 1 or 4 trials