Incorporation of the National Institute of Health (NIH) sex as a biological variable policy by R01 grant awardees

Abstract Background The National Institutes of Health (NIH) Sex as a Biological Variable (SABV) policy aims to improve the rigor and reproducibility of biomedical research by encouraging sex-inclusive study designs and sex-based analyses. Methods To evaluate policy implementation, we examine 574 funded publications (2017–2024) linked to grants from 21 NIH Institutes and Centers. We assess sex inclusion and sex-based reporting and analyses, while examining associations with author gender. Results Sixty-one percent of studies include both sexes, with human-subject research more likely to do so than non-human studies (p = 1.31×10-23). Of the single-sex studies, 34% focus on sex-specific topics. Among studies to include both sexes, 83% report sample sizes by sex, yet only 44% conduct sex-based analyses. Sex-based analyses are more common in human-subject studies (p = 0.00002) and in articles with women first authors (50% vs. 39%, p = 0.036). Articles with women as first and last author dyads are significantly more likely to analyze data by sex (OR = 2.24, 95% CI: 1.33–3.79). Conclusions These findings suggest that while the SABV policy has encouraged sex inclusion, gaps remain in sex-based analyses. Author gender may influence these research practices, underscoring the need for continued efforts to fully integrate SABV into NIH-funded research studies.