Neurology, Psychiatry Studies Overlook Sex as a Variable

A large of studies in neurology and psychiatry over the past decade percentage have failed to account for differences between the sexes, according to a team of Canadian researchers.

In a survey of more than 3000 papers published in six neuroscience and psychiatry journals from 2009 to 2019, researchers found that only 5% analyzed sex as a variable.



Liisa AM Galea, PhD

“Despite the fact there are papers that are using males and females in the studies, they’re not using the males and females in the way that would optimally find the possibility of sex differences,” lead author Liisa AM Galea, PhD, told Medscape Medical News. Galea is a professor and distinguished scholar at the Djavad Mowafaghian Center for Brain Health at the University of British Columbia in Vancouver, Canada.

The study was published online on April 19 in Nature Communications.

Optimal Design Uncommon

Differences in how neurologic and psychiatric diseases affect men and women have been well documented. Women, for example, are more susceptible to severe stroke, and men are more prone to cognitive decline with schizophrenia. With Alzheimer’s disease, women typically have more severe cognitive defects.

The researchers surveyed 3193 papers that included a multitude of studies. Although most of the papers reported studies that included both sexes, only 19% of surveyed studies used what Galea called an optimal design for the discovery of sex differences. “What I mean by ‘optimally’ is the design of the experiments and the analysis of sex as a variable,” she said. And in 2019, only 5% of the studies used sex as a variable for determining differences between the sexes, the study found.

In the current research, two authors read the methods and results of each study described in each paper, Galea said. The readers noted whether the paper reported the study sample size and whether the studies used a balanced design. The surveyed journals include Nature Neuroscience, Neuron, Journal of Neuroscience, Molecular Psychiatry, Biological Psychiatry, and Neuropsychopharmacology.

‘Not Much Is Changing’

“I had a suspicion that this was happening,” Galea said. “I didn’t know that it’s so bad, to be fair.” The “good news story,” she said, is that more papers considered sex as a factor in the later years surveyed. In 2019, more than 95% of papers across both disciplines reported participants’ sex, compared with about 70% in 2009. However, less than 20% of the papers in all study years reported studies that used sex optimally to determine differences between the sexes .

“The other thing that shocked me,” Galea said, “was that even despite the fact that we saw this increase in the number of papers that were using males and females, we didn’t see the sort of corresponding increase in those that were using ‘optimal design’ or ‘optimal analysis,'” Galea said. In 2009, 14% of papers used optimal design and 2% used optimal analysis for determining sex differences. By 2019, those percentages were 19% and 5%, respectively.

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