By Allison Proffitt 

May 5, 2026 | In 2016, the National Institutes of Health (NIH) introduced a policy requiring grantees to consider sex as a biological variable in their experimental design, analyses, and reporting. Now a team from Northwestern University has assessed progress, highlighting significant room for improvement. They have published their findings in Communications Medicine (DOI: 10.1038/s43856-026-01547-0).  

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The team considered projects funded on R01 grants in 2017 and 2018 after the Sex as a Biological Variable (SABV) policy took effect and published between 2017 and 2023. “By focusing on R01 projects, we aimed to analyze the methods of research that were held to scientifically rigorous standards,” the authors write. More than 7,500 papers were considered and 574 were randomized to the study. The projects were linked to grants from 21 NIH Institutes and Centers and published in 403 journals.  

The researchers looked for sex inclusion, reporting, and sex-based analyses, while examining any associations between sex analyses and author gender. 

“We find that while most R01‑associated publications include both sexes, fewer than half analyze data by sex, revealing a persistent gap between sex inclusion and the research practices intended by the SABV policy,” the authors write.  

Of the 574 considered articles, 350 included both sexes, 290 provided a description of the sample size by sex, and 155 analyzed data by sex.  

Only 24 articles explicitly justified their approach to sex inclusion or the presence/absence of sex-based analyses, the authors found. “Most rationales provided were justifiable and increased clarity,” they write, “however, a few instances still cited ‘hormonal variability’ as a reason to exclude female subjects—an argument that has been debunked in animal models and is widely recognized as an inadequate justification.”  

Across the studies, research teams led by women were more likely to analyze data by sex, and researchers were more likely to include and report both sexes in human research than animal research, an area the authors highlighted as particularly in need of improvement. The SABV policy was designed to address such disparities, the authors argue. They also emphasize the need to report sex in cell-based research as well, “particularly in studies relying on immortalized cell lines where the sex of the cells is frequently unreported.”  

The team issued a challenge to the research community in general to better adhere to SABV policy, to analyze and report data by sex, particularly in preclinical studies, and—when possible, estimate effects for males and females separately.  

But the authors also called on publishers in particular to hold researchers accountable.  

“Academic journals need to be involved in this process as the final gatekeepers prior to publication,” they write. “Educating peer reviewers and journal editors, and ensuring the wide dissemination of policy updates regarding SABV to reviewers, could improve overall adherence to the NIH SABV policy and increase the rigor and generalizability of biomedical research funded by the NIH.”