top of page
Sex as a Biological Variable
What does "sex as a biological variable" refer to?
  • Link to post on Instagram

Let's talk about a biological variable in research. “Sex” is a person's reproductive/secondary sex characteristics at birth, whereas “gender” is a social role/identity. Recently, agencies funding biomedical, psychological, and neuroscience research made policies to ensure that scientists account for sex and/or gender in studies (e.g., US' NIH, the European Commission, and Canada’s CIHR).

Sushi Science | Janelle Letzen | NIH
Why should you care about this research policy?

Well, sex/gender can influence how we respond to illness and treatment from both physiological and social standpoints. Physiologically, sex differences can affect things like disease progression and drug metabolism. Socially, gender differences can affect things like providers’ likelihood to prescribe a treatment or a patient’s likelihood to seek care (for example, see reviews).There are important aspects to sex/gender. A person is considered “cisgender” when her/his sex at birth and gender match. A person is considered “transgender” when her/his sex at birth and gender do not match. A person is considered “intersex” when her/his sex at birth don’t fit into commonly described solely female or male characteristics. 

For a long time, health-related cell/animal studies used male samples/subjects, and human research used mostly cisgender males. Researchers often described results as applying to all individuals. As a result, some things that worked in the lab didn’t work in an actual clinic setting.


Policies like “Sex as a Biological Variable” aim to address this problem with poor reproducibility and translation of findings.It might sound like an obvious answer, then, to just be more inclusive and use all combinations of sex and gender in studies. But, there are challenges.


To test for sex/gender differences, studies need more subjects or samples. With larger sample sizes, the cost of running a study goes up and it can take longer for results to transition from bench to bedside.These policies represent an important step of inclusivity in research. Yet, a lot of work remains to understand how results apply to transgender and intersex people too.


[1] Lee, S. K. (2018). Sex as an important biological variable in biomedical research. BMB reports, 51(4), 167.
[2] Pardue, M. L., & Wizemann, T. M. (Eds.). (2001). Exploring the biological contributions to human health: does sex matter?. National Academies Press.
[3] Klein, S. L., & Flanagan, K. L. (2016). Sex differences in immune responses. Nature Reviews Immunology, 16(10), 626.
[4] Regitz‐Zagrosek, V. (2012). Sex and gender differences in health: Science & Society Series on Sex and Science. EMBO reports, 13(7), 596-603.
[5] Clayton, J. A., & Tannenbaum, C. (2016). Reporting sex, gender, or both in clinical research?. Jama, 316(18), 1863-1864.
[6] Fields, R. D. (2014). NIH policy: mandate goes too far. Nature, 510(7505), 340.

bottom of page