Sex differences in cognition are small

Lately I’ve been thinking about sex differences in brain and cognition. There are undeniable differences in the physical size of the brain, and different brain areas, even if there are no ‘female’ and ‘male’ brains categorically. These physical differences do not translate directly into commensurate differences in cognition. Indeed, there is support for a ‘gender similarities hypothesis’ which asserts that on most measures there is no difference between men and women.

Most, but maybe not all. There are a few areas of fundamental cognitive ability where gender differences seem to persist – mental rotation, vocabulary and maybe maths. But these differences are small. To see how small, I put them on the same chart with the physical differences and a few other behavioural differences for perspective.

Standardised mean differences (Cohen’s d effect size) for various gender differences in brain, behaviour and cognition:

gender_effectsReferences and calculations at the end of this post, below the fold. And if you need a primer on what is meant by standardised difference then go here.

Even with these, small, observed differences in cognition, we don’t know what proportion is due to contingent facts, such as the different experience and expectations men and women encounter in their lifetimes, and what proportion is immutable consequence of genetic difference in sex.

One possibility for why there is a mismatch between physical differences in the brain and cognitive differences is the possibility that structural differences between male and female brains may actually serve to support functional similarity, not difference.

For more, so much more, on this, see the special issue of Journal of Neuroscience Research (January/February 2017) on An Issue Whose Time Has Come: Sex/Gender Influences on Nervous System Function.

Includes: Grabowska, A. (2017). Sex on the brain: Are gender‐dependent structural and functional differences associated with behavior?. Journal of Neuroscience Research, 95(1-2), 200-212.

Previously: Gender brain blogging

Calculations & References:

Height: Cohen’s d = 1.72. Taken from Wikipedia page on Effect Sizes (if anyone has the proper reference, let me know)

Sexual preference: d = 1.62. First, assume sexual preference and gender are binary. Although these assumptions are incorrect and harmful to individuals, in terms of effect size all this does it contribute to an overestimation of any sex difference. Next, calculate odds that someone has a sexual preference for men if they are a women vs are a man. Estimates of non-hetrosexual preference vary from 2%-10% (here’s some discussion). This gives odds ratio of 39 (for 2% non-hetrosexuality), 19 (for 5%) or 9 (for 10%). Convert to Cohen’s d using using d = log(OR)/1.81, as per Chinn, S. (2000). A simple method for converting an odds ratio to effect size for use in meta-analysis. Statistics in medicine, 19(22), 3127-3131.

Brain volume: d= 1.4. See Sex differences in brain size

Mental rotation: d = 0.62. See Hyde, J. S. (2016). Sex and cognition: gender and cognitive functions. Current opinion in neurobiology, 38, 53-56. May be an overestimate, but is generally reported to be the largest, and most robust, sex difference in cognition.

Left handedness: d = 0.11 (OR = 1.23). Papadatou-Pastou, M., Martin, M., Munafo, M. R., & Jones, G. V. (2008). Sex differences in left-handedness: a meta-analysis of 144 studies. Psychological Bulletin, 134(5), Sep 2008, 677-699

Maths: d = 0.05. See Hyde, J. S. (2016). Sex and cognition: gender and cognitive functions. Current opinion in neurobiology, 38, 53-56.

Vocabulary: d = -0.11. See Hyde, J. S. (2016). Sex and cognition: gender and cognitive functions. Current opinion in neurobiology, 38, 53-56.

15 thoughts on “Sex differences in cognition are small”

    1. Differences in brain volume and structure do not automatically lead to differences in cognition. Measuring cognition is the best way to understand cognition. You may find the links in the post (e.g. the second one) useful.

      1. Hi – In a previous post you said that “Gender differences in ability may be overinflated in the popular imagination” but I wonder if the “popular imagination” of gender differences relates more to differences in preferences, emotion, motivation, empathy, value-based decisions rather than the more narrowly defined cognitive abilities. The latter are psychological variables too (albeit much harder to measure) so I would want to know about brain differences that relate to these variables before drawing the conclusion “males and females are quite similar on most — but not all — psychological variables” (Hyde, 2016). I realize the discussion is about cognition specifically but I am concerned that readers will assume cognitive similarities means similarity in all psychological variables.

  1. I am assuming that all these cognition studies are done on European or American humans as opposed to, say Native American, Eskimo, African etc humans? That being the case (as it most undoubtedly is) then perhaps these differences might be found to be largely culturally induced (women are expected to have “rotational deficiency” in our culture due to “map reading skills” fr instance, but Eskimo women have no such deficiency because their skills are developed from childhood, etc)

    1. @carol – yes, differences in adults will be, to some extent, due to gender-contigent life experience. Cross-cultural studies are one way of assessing how large that extent is. Do you have a reference for mental rotation performance among the Inuit?

      @y_psych – hopefully readers will heed the warning that you raise in your comment. The note I make in the last post is also relevant, about why we focus on cognition (because it is assumed to reflect something more fundamental?)

    1. Really interesting article, David. In any case more honest than the “there are no gender differences although we can distinguish gender in the brain with above 90% accuracy”. Neuroscience is becoming the new cultural anthropology in American academia.

  2. Here’s one VERY SIGNIFICANT way that male brains and female brains are different …
    “the right orbitofrontal cortex, the attachment control system, functionally matures according to different timetables in females and males, and thus, differentiation and growth stabilizes earlier in females than in males (A.N. Schore, 1994).” This leaves boys more vulnerable to maternal stress and depression in the womb, birth trauma (e.g., separation from mother), and to unresponsive caregiving (caregiving that leaves them in distress).
    https://acestoohigh.com/2017/02/14/be-worried-about-boys-especially-baby-boys/#more-6534

  3. I’m very much enjoying this series of posts – thanks, Tom!

    I don’t know if it’s *the* reference, but the paper I cite for the sex difference in height is usually this one (they report d = 1.75):

    Lassek, W. D., & Gaulin, S. J. (2009). Costs and benefits of fat-free muscle mass in men: Relationship to mating success, dietary requirements, and native immunity. Evolution and Human Behavior, 30(5), 322-328.

    pdf here: https://www.researchgate.net/profile/Steven_Gaulin/publication/247233659_Costs_and_benefits_of_fat-free_muscle_mass_in_men_Relationship_to_mating_success_dietary_requirements_and_native_immunity/links/5404a09e0cf23d9765a69033/Costs-and-benefits-of-fat-free-muscle-mass-in-men-Relationship-to-mating-success-dietary-requirements-and-native-immunity.pdf

  4. In the tenth chapter of my current psychology class, we find that there are differences in the brain between male and females, particularly when it comes to sexual orientation. First, there are some basic differences between the two sexes. However, in homosexual men, a few of their brain structures take on a tendency toward the female setup. This is a two way street, as homosexual women have a shift toward the male structure. In heterosexual females, the right and left parts of the cerebral cortex are relatively the same size. However, the left hemisphere is a bit smaller in heterosexual males. The left amygdala is more widespread in heterosexual females, whereas it is the right amygdala in heterosexual males. Though there are several other differences in brain structure, it still remains unclear if these differences are the cause or the effect of any given sexual orientation. Recurring behaviors can influence anatomy and structure, but differences in structure can also predispose a person to certain conditions.

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