Peer reviewers’ conflicts of interest in biomedical research: scoping review
Authors: Korfitsen Christoffer Bruun , Nejstgaard Camilla Hansen , Hróbjartsson Asbjørn , Boutron Isabelle , Bero Lisa , Lundh Andreas 
Published: January 2025

BackgroundPeer review may improve the quality of research manuscripts and aid in editorial decisions, but reviewers can have conflicts of interest that impact on their recommendations.ObjectivesThe objective was to systematically map and describe the extent and nature of empirical research on peer reviewers’ conflicts of interest in biomedical research.DesignScoping reviewMethodsIn this scoping review, we included studies investigating peer reviewers’ conflicts of interest in journal manuscripts, theses and dissertations, conference abstracts, funding applications and clinical guidelines. We searched MEDLINE, Embase, The Cochrane Methodology Register, Google Scholar (up to January 2024) and other sources. Two authors independently included studies and extracted data on key study characteristics and results, and we organised data by study domain (eg, journal manuscripts) and study aims. We included studies directly investigating peer reviewers’ conflicts of interest in our primary analysis, and studies investigating other questions (eg, reasons for retraction), but reporting relevant data on peer reviewers’ conflicts of interest, were solely included in a supplementary analysis.ResultsAfter screening 44 353 references, we included 71 studies, of which 41 were included in our primary analysis. The 41 studies were published between 2005 and 2023, and 34 (83%) were journal publications. 30 (73%) studies investigated journal manuscripts, 1 (2%) conference abstracts, 4 (10%) funding applications and 6 (15%) clinical guidelines. No studies investigated theses or dissertations. 37 (90%) studies used quantitative research methods, 2 (5%) qualitative and 2 (5%) mixed methods. 21 (51%) studies investigated both financial and non-financial interests, 6 (15%) solely financial interests, 5 (12%) solely non-financial interests and 9 (22%) did not report the type of interest. We organised included studies based on study aims, with some studies having multiple aims: impact on recommendations (one study), occurrence of peer reviewers’ conflicts of interest (11 studies), stakeholders’ experiences (13 studies) and policy and management (22 studies). One (2%) study investigated the impact of peer reviewers’ personal connections with authors on reviewers’ recommendations. Nine (22%) studies estimated prevalences of conflicts of interest among peer reviewers, ranging from 3%–91%. Two (5%) studies both reported that conflicts of interest were a reason for declining to review in 1% of cases. 13 (32%) studies investigated stakeholders’ experiences with peer reviewers’ conflicts of interest, primarily using questionnaires of reviewers, editors and researchers. 16 (39%) studies estimated prevalences of having conflict of interest policies for peer reviewers, ranging from 5%–96%, among journals, conferences and clinical guideline organisations. Finally, six (15%) studies estimated prevalences of public availabilities of reviewers’ conflicts of interest declarations, ranging from 0%–71%.ConclusionsMost studies addressed conflicts of interest in peer review of journal manuscripts, primarily through surveys of journal policies or questionnaires of researchers, editors and peer reviewers. The impact of peer reviewers’ conflicts of interest on recommendations and their prevalence is still poorly understood. Our results can guide future studies and be used to align policies and management of peer reviewers’ conflicts of interest.Study registrationOpen Science Framework (DOI: 10.17605/OSF.IO/9QBMG).