The push to encourage women to enter STEM fields has become so ubiquitous that there are op-eds written seemingly every week, a dedicated page on the White House website, and even a line of interactive dolls. A lesser-known gender discrepancy in science, however, is the lack of female research subjects. Despite a 1993 law requiring women and minorities to be included as subjects in clinical research funded by the National Institutes of Health, women continue to be under-represented.

Of course, clinical trials (testing medical interventions on human subjects) are only a small subset of medical studies. Other types of research that inform health care practices are conducted on animals and cells, and those studies, researchers at Northwestern University say, are also vulnerable to sex bias.

The results are especially alarming for female-prevalent disorders like thyroid and cardiovascular disease—only 12 percent of these studies included female subjects.

In a new study published in September’s issue of Surgery, vascular surgeon Melina R. Kibbe and her colleagues examine studies from 2011 to 2012 from the top five general surgery journals. They found a total of 618 publications using animals and/or cells.

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