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Searching for unpublished data for Cochrane reviews: cross-sectional study

Date and Location




Sunday 22 September 2013 - 10:30 - 12:00


Presenting author and contact person

Presenting author

Jeppe Schroll

Contact person

Jeppe Schroll
Abstract text
Background: Failure to include unpublished data in meta-analyses will generally lead to too positive results. New sources of unpublished data have become available in recent years but it is unknown to what extent such data are being used. Objectives: To describe the experiences that Cochrane authors have with searching for, getting access to and using unpublished data. Methods: Cross-sectional survey of corresponding authors of Cochrane reviews. Authors were invited by e-mail to an online survey which contained open-ended and closed questions. Results: We sent 5,915 invitations and got 2,184 replies (37% response rate). Of those, 1,656 (76%) had searched for unpublished data. In 913 cases (55%), new data were obtained, and details about these data were provided in 794 cases. The most common data source was trialists / investigators accounting for 74% (n=587) of the 794 data sources. Most of the data were used in the review (82%, 651/794) and 54% (424/794) received their data in less than a month. Most common were summary data, which 51% (403/794) of the data sources provided, whereas 21% (163/794) provided individual patient data. Only 6% (50/794) reported to have obtained data from the manufacturers and this group waited longer and used more contacts to get the data. The data from manufacturers were less likely to be individual patient data and less likely to be used in the review. Data from regulatory agencies accounted for 3% (24/794) of the obtained data. Conclusions: Most authors that searched for unpublished data received useful data, primarily from trialists. Manufacturers and regulatory agencies were uncommon sources of unpublished data.