A study in the US has found that many studies fail to analyse male and female data separately, despite progress following the implementation of a policy to encourage sex inclusion. 

Biomedical studies have historically favoured male subjects, limiting our understanding of female biology, with implications for scientific progress and drug development. In 2016, the National Institute of Health (NIH), implemented the ‘Sex as a Biological Variable (SABV)’ policy, which requires that studies funded by NIH consider sex in their experimental design, analysis and reporting.  

To evaluate the implementation of the policy, researchers from Northwestern University analysed 574 NIH-funded publications between 2017 and 2024, including 283 human studies, 266 using animals and 25 using both, and found that, even though 61% included male and female subjects, fewer than half of those studies broke down findings by sex (44%). Studies with women as first and last authors were 2.24 times more likely to conduct separate analyses by sex.  

“Just including women is not enough. When scientists simply check a box to say they included women, but fail to analyze the data by sex, we lose the ability to understand whether or how treatments affect men and women differently. That limits our capacity to advance precision medicine and improve care for everyone,” said Nicole Woitowich, researcher of medical social sciences at Northwestern University and leader of the study published in Communications Medicine.  

The team found that 78% of human studies included both sexes, compared with 41% of animal studies, which limits early understanding of sex differences and increases the risk of adverse effects later on, in human studies.  

“It takes larger studies to conduct robust sex-specific analyses, but making the effort means that we have a better shot at drug development — and ultimately patient care — that benefits everyone,” said study author Leah Welty, also from Northwestern University.