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 fra 2022 sammenlignet 24 menn, 24 kvinner og 24 transkvinner som ennå ikke brukte hormoner, med en datamodell som skårer hjerner på én enkelt skala fra mannlig til kvinnelig. Den konkluderte med at transkvinnenes hjerner var forskjøvet bort fra fødselskjønnet og mot kjønnsidentiteten.
• Studien testet bare for en forskjell i én retning. Når man tester begge retninger, som vanlig, blir den viktigste forskjellen mellom transkvinner og menn svakere. Når man justerer for at tre sammenligninger ble gjort, kan den lett være tilfeldig.
• Den større forskjellen mellom transkvinner og kvinner ville fortsatt holde etter disse justeringene. Så striden gjelder om transkvinners hjerner er forskjellige fra menns, ikke om de er forskjellige fra kvinners.
• Med bare 24 personer per gruppe er størrelsen på en eventuell forskjell ustabil. Ett uvanlig resultat i mannsgruppen ble aldri kontrollert ved å kjøre analysen på nytt uten det.
• Testen studien brukte for å begrunne den statistiske metoden er svak med så små grupper. Kritikerne sier at metoder som gjør færre antakelser i det minste burde ha vært rapportert også.
• Av de 24 transkvinnene var 6 tiltrukket av menn og 18 av kvinner. Seksuell orientering henger sammen med hjernestruktur, og de opprinnelige forfatterne hadde disse dataene, men tok ikke hensyn til dem.
• Hver av kritikerne ba gjentatte ganger om de opprinnelige dataene og fikk ikke svar, så kritikken bygger på publiserte tall. De etterlyser at dataene frigis og at studien gjentas av andre.

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.