Gender Differences Masquerading as Sex Differences

Should we use “sex” and “gender” interchangeably when discussing people? A recent article in the prestigious academic journal, Proceedings of the National Academy of Sciences (PNAS), provides one example of how this word choice matters.

The article was entitled, “Sex bias in pain management decisions.” The authors said they investigated “the effects of patients’ sex rather than gender because gender identity was not recorded.” This study was also highlighted in the news section of the journal, Science, which echoed that the study focused on sex, not gender.

Sex is biological and can be defined by chromosomes, gonads, or genitals, though these three measures sometimes point in different directions. In nonhuman animal studies, researchers typically examine genitals and/or gonads, if not chromosomes, to determine each subject’s sex. In human studies, however, subjects typically mark a box on a form, “male” or “female.” This most likely indicates the subject’s own perception of themselves as a man or woman—their gender—which may or may not match their biological sex.

This recent PNAS study showed that physicians are less likely to prescribe pain medication for women than for men. In other words, physicians treat patients differently depending on their perception of the patient’s gender, which itself likely depends on the patient’s gender expression. That is, many physicians have a gender bias. This is a very important point, but it is not directly related to the biological sex of the patient.

Descriptions of “sex differences” that are really gender differences likely occur in many other human studies. One reason for this may be that since 2016, the National Institutes of Health “expects that sex as a biological variable will be factored into research designs, analyses, and reporting in vertebrate animal and human studies.” In practice, this means researchers must explain how they will take sex into account when they propose and conduct their studies. The simplest way to take sex into account is to categorize each subject as male or female and then look for a difference in the male and female averages for whatever parameters they measure.

This NIH rule likely increased reports of “sex differences” in both nonhuman animals and humans, but such statements can be misleading. Even if there is a sex difference on average, this difference may be too small to be physiologically meaningful, it may obscure large overlap in the values measured in females and males, and it may encourage follow-up studies to focus on effects of sex when other factors actually have a larger impact. For example, the difference found may be caused by another biological factor that is usually correlated with sex, such as a hormone concentration, iron level, body fat composition, etc.

This NIH rule may also have provided an incentive for researchers conducting human studies to say they are examining effects of sex when they are actually looking at effects of gender. Mixing up sex and gender can alter understanding of causality and determination of next steps. If there is a sex difference, it likely has a biological cause that may necessitate a difference in biological treatment. But if there is instead a gender difference, it may necessitate education or training in gender-based attitudes.

For example, if the recent study had discovered a sex difference in pain between females and males, that would indicate a difference in how the nervous systems of females and males respond to potentially painful conditions. In that case, different medications or dosages might be required to treat comparable painful conditions in females vs. males. (To be clear, the PNAS authors did not argue that there is a biological difference in males’ and females’ pain mechanisms.)

But this study actually showed that physicians treat patients’ pain differently depending on the physician’s perception of the patient’s gender. This finding does not suggest that females require more or different pain medication than males. It instead suggests that physicians need to become aware of their own gender biases to avoid undertreating women’s pain in comparable situations.

In general, saying “sex” when you mean “gender” may inadvertently make people think that a difference revealed has a biological cause—which can be addressed effectively via a different biological treatment—when there is actually a social or cultural cause, which can only be addressed through a social or cultural change.

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People also sometimes say “gender” when they really mean biological sex, presumably because they are just not comfortable using the word, “sex.” This can also be misleading, because it may make readers think there is a cultural or social cause of an outcome that actually has a strictly biological cause.

So using “sex” and “gender” correctly can make a big difference in how we understand causes of differences between groups of people and how best to address them.