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

• Studien från 2022 jämförde 24 män, 24 kvinnor och 24 transkvinnor som ännu inte tog hormoner, med en datormodell som poängsätter hjärnor på en enda skala från man till kvinna. Den drog slutsatsen att transkvinnornas hjärnor var förskjutna bort från deras biologiska kön mot deras könsidentitet.
• Studien testade bara för en skillnad i en riktning. Att testa i båda riktningarna, som är vanligt, gör den viktiga skillnaden mellan transkvinnor och män svagare. Justering för att tre jämförelser gjordes innebär att den lätt kan bero på slumpen.
• Den större skillnaden mellan transkvinnor och kvinnor skulle fortfarande hålla efter dessa justeringar. Så tvisten gäller om transkvinnors hjärnor skiljer sig från mäns, inte om de skiljer sig från kvinnors.
• Med bara 24 personer per grupp är storleken på en eventuell skillnad instabil. Ett ovanligt resultat i mansgruppen kontrollerades aldrig genom att köra om analysen utan det.
• Testet som studien använde för att motivera sin statistiska metod är svagt med så små grupper. Kritikerna säger att metoder som gör färre antaganden åtminstone borde ha redovisats också.
• Av de 24 transkvinnorna var 6 attraherade av män och 18 av kvinnor. Sexuell läggning hänger samman med hjärnans struktur, och de ursprungliga författarna hade dessa data men tog inte hänsyn till dem.
• Varje kritiker bad upprepade gånger om originaldata och fick inget svar, så kritiken bygger på publicerade siffror. De efterlyser att data släpps och att studien upprepas av andra.

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.