02473nas a2200205   4500000000100000008004100001260001500042100002200057700002200079700001800101700001400119700002500133700002300158245013500181856004400316300001200360490000700372520187400379022001402253       2026                            d  c2026-01-011 aCatharine E Krebs1 aIgnacio J Tripodi1 aPandora Pound1 aRon Baron1 aFrancesca Pistollato1 aHelder Constantino00aEvidence of animal methods bias in manuscript peer review: Results from a survey of in vitro researchers and bibliometric analyses  uhttps://doi.org/10.1093/reseval/rvag063  arvag0630 v353 aAnimal methods bias is a peer review bias characterized by a preference for animal-based biomedical research methods or lack of expertise to adequately evaluate nonanimal methods, like complex in vitro models. Preliminary evidence indicates that some manuscript reviewers request animal experiments, which authors often feel are not scientifically justified. We explored this through a cross-sectional survey of 189 biomedical researchers and bibliometric analyses. Fifty-two percent of survey respondents had been asked to add animal experiments to nonanimal studies during manuscript review. On average, authors refused 79% of these requests, citing reasons like lack of necessity or feasibility. Moreover, 46% felt their nonanimal studies received unfair reviews due to absence of animals. Most respondents (84%) reported negative consequences, like publishing in lower-impact journals (65%), rejection (49%), and publication delays (42%). To triangulate self-reported findings, we investigated over 1.1 million publications (2009–2023), identifying significantly higher journal impact factors for studies using animal versus in vitro methods, although differences varied by field. Additionally, we created a natural language processing pipeline to analyze 304,849 animal-based publications and compare species used in 3,159 corresponding preprints. We identified 17 studies where an animal experiment was introduced after the first preprint version was posted, suggesting that authors occasionally add them after original study completion. Animal methods bias presents challenges for researchers using animal-free methods and addressing it is essential as funding bodies increasingly invest in nonanimal approaches to improve translatability. These findings help elucidate animal methods bias and highlight a critical challenge for biomedical research evaluation.  a0958-2029