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

• Lo studio del 2022 confrontava 24 uomini, 24 donne e 24 donne transgender non ancora in terapia ormonale, usando un modello informatico che assegna ai cervelli un punteggio su un'unica scala da maschile a femminile. Concludeva che i cervelli delle donne trans erano spostati dal loro sesso di nascita verso la loro identità di genere.
• Lo studio ha verificato solo una differenza in una direzione. Verificandola in entrambe le direzioni, come di consueto, la differenza chiave tra donne trans e uomini si indebolisce. Correggendo per il fatto che sono stati fatti tre confronti, potrebbe facilmente essere dovuta al caso.
• La differenza più ampia tra donne trans e donne reggerebbe comunque dopo queste correzioni. La disputa riguarda quindi se i cervelli delle donne trans differiscano da quelli degli uomini, non se differiscano da quelli delle donne.
• Con soli 24 individui per gruppo, l'entità di qualsiasi differenza è instabile. Un risultato insolito nel gruppo degli uomini non è mai stato verificato rifacendo l'analisi senza di esso.
• Il test usato dallo studio per giustificare il proprio metodo statistico è debole con gruppi così piccoli. I critici dicono che avrebbero dovuto almeno essere riportati anche metodi che fanno meno ipotesi.
• Delle 24 donne trans, 6 provavano attrazione per gli uomini e 18 per le donne. L'orientamento sessuale è legato alla struttura del cervello, e gli autori originali avevano questi dati ma non ne hanno tenuto conto.
• Ciascun critico ha chiesto più volte i dati originali senza ricevere risposta, quindi la critica si basa sulle cifre pubblicate. Chiedono che i dati vengano rilasciati e che lo studio sia ripetuto da altri.

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.