Abstract
As part of an initiative to improve rigor and reproducibility in biomedical research, the U.S. National Institutes of Health now requires the consideration of sex as a biological variable in preclinical studies. This new policy has been interpreted by some as a call to compare males and females with each other. Researchers testing for sex differences may not be trained to do so, however, increasing risk for misinterpretation of results. Using a list of recently published articles curated by Woitowich et al. (eLife, 2020; 9:e56344), we examined reports of sex differences and non-differences across nine biological disciplines. Sex differences were claimed in the majority of the 147 articles we analyzed; however, statistical evidence supporting those differences was often missing. For example, when a sex-specific effect of a manipulation was claimed, authors usually had not tested statistically whether females and males responded differently. Thus, sex-specific effects may be over-reported. In contrast, we also encountered practices that could mask sex differences, such as pooling the sexes without first testing for a difference. Our findings support the need for continuing efforts to train researchers how to test for and report sex differences in order to promote rigor and reproducibility in biomedical research.
Highlights
Biomedical research has not considered sex as a biological variable (SABV)
In our sample of articles in which data were reported by sex, a sex difference was reported in more than half of the articles and in half of those, the difference was treated as a major finding by highlighting it in the title or abstract
We cannot rule out the possibility, that the researchers following National Institutes of Health (NIH) guidelines are primarily those that are interested in sex differences
Summary
Biomedical research has not considered sex as a biological variable (SABV). In a cross-disciplinary, quantitative assessment of the 2009 biomedical literature, Beery and Zucker, 2011, found a concerning bias toward the use of males only As awareness of this issue increased, in 2016 the National Institutes of Health (NIH) implemented a policy requiring consideration of SABV in the design, analysis, and reporting of all NIH-funded preclinical research (NIH, 2015; Clayton, 2018). Since 2016, NIH has made available a number of resources, including training modules, administrative funding supplements, and a center program focused on sex differences (Arnegard et al, 2020) These efforts have resulted in the discovery of new sex differences across a wide spectrum of research fields (Arnegard et al, 2020)
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