Reporting of funding and conflicts of interest improved from preprints to peer-reviewed publications of biomedical research.

Background and Objectives: To assess changes in the reporting of funding and conflicts of interest (COI) in biomedical research between preprint server publications and their corresponding versions in peer-reviewed journals.
Methods: We selected preprint servers publishing exclusively biomedical research. From these, we screened articles by order of publication date and identified 200 preprints first published in 2020 with subsequent versions in peer-reviewed journals. We judged eligibility and extracted data about authorship, funding, and COI in duplicate and independently. We performed descriptive statistics.
Results: A quarter of the studies added at least one author to the peer-reviewed version. Most studies reported funding in both versions (87%), and a quarter of these added at least one funder to the peer-reviewed version. Eighteen studies (9%) reported funding only in the peer-reviewed version. A majority of studies reported COI in both versions (69%) and 5% of these had authors reporting more COI in the peer-reviewed version. A minority of studies (23%) reported COI only in the peer-reviewed version. None of the studies justified any changes in authorship, funding, or COI.
Conclusion: Reporting of funding and COI improved in peer-reviewed versions. However, substantive percentages of studies added authors, funders, and COI disclosures in their peer-reviewed versions.
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