Summary

A widely cited 2022 brain-scan study by Kurth and colleagues reported that the brains of 24 transgender women, before hormone treatment, fell between those of men and women, though closer to men. This 2026 critique argues the key difference from men only looked real because of lenient statistical choices: testing in one direction only, and not adjusting for making three comparisons. With standard adjustments, the difference from men could easily be chance, though the difference from women still holds. Small groups and one unusual result make it fragile. Sexual orientation, known to relate to brain structure, was never analysed though the data existed. The critique is plausible but uses only published figures, was accepted nine days after it was sent in, and its lead author is a Manhattan Institute fellow on the journal's advisory board.

Key findings

• Studie z roku 2022 porovnala 24 mužů, 24 žen a 24 transgender žen, které ještě neužívaly hormony, pomocí počítačového modelu, který bodoval mozky na jediné škále od mužského po ženský. Dospěla k závěru, že mozky trans žen byly posunuty od jejich pohlaví při narození směrem k jejich genderové identitě.
• Studie testovala rozdíl jen v jednom směru. Testování obou směrů, jak je obvyklé, činí klíčový rozdíl mezi trans ženami a muži slabším. Po úpravě na to, že byla provedena tři srovnání, mohl snadno být náhodný.
• Větší rozdíl mezi trans ženami a ženami by po těchto úpravách stále platil. Spor tedy je o tom, zda se mozky trans žen liší od mužských, ne zda se liší od ženských.
• Při pouhých 24 lidech na skupinu je velikost jakéhokoli rozdílu nestabilní. Jeden neobvyklý výsledek ve skupině mužů nebyl nikdy zkontrolován opakováním analýzy bez něj.
• Test, který studie použila k ospravedlnění své statistické metody, je u tak malých skupin slabý. Kritici říkají, že metody s menším počtem předpokladů měly být alespoň také uvedeny.
• Ze 24 trans žen bylo 6 přitahováno k mužům a 18 k ženám. Sexuální orientace souvisí se stavbou mozku a původní autoři tato data měli, ale nezohlednili je.
• Každý z kritiků opakovaně žádal o původní data a nedostal odpověď, takže kritika spoléhá na publikované údaje. Vyzývají k uvolnění dat a k zopakování studie jinými.

Abstract

Kurth et al. (2022) concluded that the brain anatomy of transgender women is shifted away from their biological sex and toward their gender identity. We evaluate whether the study’s evidence supports this conclusion by focusing on its statistical methods and treatment of sexual orientation in its analyses. The principal finding relies on a very small sample, a weak justification for parametric analyses, one-tailed post hoc tests, no correction for multiple comparisons, and limited robustness testing. The study also did not properly account for sexual orientation as a potential neuroanatomical confound despite having the relevant participant data to do so. These methodological choices consistently bias the results toward smaller p-values and stronger apparent support for the authors’ stated hypothesis. The evidence presented therefore does not justify the study’s headline conclusion.

Conclusion

The analyses presented do not adequately support the paper's headline conclusion that transgender women's brains are shifted toward their gender identity. The evidence used to support that conclusion is weakened by a series of methodological limitations and poor choices, including a small sample size, parametric statistical methods, one-tailed post hoc hypothesis tests without correction for multiple comparisons, and the absence of several robustness analyses. The study also does not address sexual orientation as a potential confound, despite the authors possessing both the neuroanatomical and sexual orientation data needed to evaluate this possibility. These methodological choices and omissions consistently strengthen the perceived support for the authors' stated hypothesis while weakening confidence in the reported findings. Given the paper's unusually broad influence in neuroscience, medicine, journalism, law, and public policy, the methodological issues warrant careful consideration before the study can be cited as evidence supporting the hypothesis, and the authors welcome a response from the original authors and encourage public release of the anonymized participant-level data so that the findings can be independently replicated and evaluated.