The sociology of scientific validity: How professional networks shape judgement in peer review

Professional connections between the creators and evaluators of scientific work are ubiquitous, and the possibility of bias ever-present. Although connections have been shown to bias predictions of uncertain future performance, it is unknown whether such biases occur in the more concrete task of assessing scientific validity for completed works, and if so, how. This study presents evidence that connections between authors and reviewers of neuroscience manuscripts are associated with biased judgments and explores the mechanisms driving that effect. Using reviews from 7981 neuroscience manuscripts submitted to the journal PLOS ONE, which instructs reviewers to evaluate manuscripts on scientific validity alone, we find that reviewers favored authors close in the co-authorship network by ∼0.11 points on a 1.0–4.0 scale for each step of proximity. PLOS ONE's validity-focused review and the substantial favoritism shown by distant vs. very distant reviewers, both of whom should have little to gain from nepotism, point to the central role of substantive disagreements between scientists in different professional networks (“schools of thought”). These results suggest that removing bias from peer review cannot be accomplished simply by recusing closely connected reviewers, and highlight the value of recruiting reviewers embedded in diverse professional networks.