Biological Research Often Incorrectly Reports Sex Differences
An analysis of published studies from a range of biological specialties shows that when data are reported by sex, critical statistical analyses are often missing and the findings are likely to be reported in misleading ways.
The analysis was published in the journal eLife.
“We found that when researchers report that males and females respond differently to a manipulation such as a drug treatment, 70% of the time the researchers have not actually compared those responses statistically at all,” said senior author Donna Maney, a professor of neuroscience in Emory’s Department of Psychology. “In other words, an alarming percentage of claims of sex differences are not backed by sufficient evidence.”
In the articles lacking the proper evidence, she added, sex-specific effects were claimed almost 90% of the time. In contrast, authors that tested statistically for sex-specific effects only reported them 63% of the time.
”Our results suggest that researchers are predisposed to finding sex differences and that sex-specific effects are likely over-reported in the literature,” Prof Maney said.
The problem is so pervasive not even her own work was safe. “Once I realised how prevalent it is, I went back and checked my own published articles and there it was,” she said. “I myself have claimed a sex difference without comparing males and females statistically.”
Prof Maney stressed that the problem should not be discounted; it is becoming increasingly serious, she said, because of mounting pressure from funding agencies and journals to study both sexes, and interest from the medical community to develop sex-specific treatments.
Better training and oversight are needed to ensure scientific rigor in research on sex differences, the authors wrote: “We call upon funding agencies, journal editors and our colleagues to raise the bar when it comes to testing for and reporting sex differences.”
Historically, biomedical research has often included just one sex, usually biased toward males. In recent decades, laws have been passed requiring US medical research to include females in clinical trials and report the sex of human participants or animal subjects.
“If you’re trying to model anything relevant to a general population, you should include both sexes,” Prof Maney explained. “There are a lot of ways that animals can vary, and sex is one of them. Leaving out half of the population makes a study less rigorous.”
As more studies consider sex-based differences, Maney adds, it is important to ensure that the methods underlying their analyses are sound.
For the analysis, Prof Maney and co-author Yesenia Garcia-Sifuentes, PhD candidate, looked at 147 studies published in 2019 to see what is used for evidence of sex differences. The studies ranged across nine different biological disciplines, including field studies on giraffes and immune responses in humans.
The studies that were analysed all included both males and females and separated the data by sex. Garcia-Sifuentes and Prof Maney found that the sexes were compared, either statistically or by assertion, in 80% of the articles. Of those articles, sex differences were reported in 70% of them and of those treated as a major finding in about half.
Statistical errors were seen in some studies, with a significant difference for one sex but not the other counted as a difference between them. The problem with that approach is that the statistical tests conducted on each sex can’t give “yes” or “no” answers about whether the treatment had an effect.
“Comparing the outcome of two independent tests is like comparing a ‘maybe so’ with an ‘I don’t know’ or ‘too soon to tell,'” Maney explains. “You’re just guessing. To show actual evidence that the response to treatment differed between females and males, you need to show statistically that the effect of treatment depended on sex. That is, to claim a ‘sex-specific’ effect, you must demonstrate that the effect in one sex was statistically different from the effect in the other.”
Conversely, their analysis also encountered strategies that could mask sex differences, such as pooling data from males and females without testing for a difference.
“At this moment in history, the stakes are high,” Maney says. “Misreported findings may affect health care decisions in dangerous ways. Particularly in cases where sex-based differences may be used to determine what treatment someone gets for a particular condition, we need to proceed cautiously. We need to hold ourselves to a very high standard when it comes to scientific rigor.”
Source: EurekAlert!