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

• O estudo de 2022 comparou 24 homens, 24 mulheres e 24 mulheres transgênero que ainda não usavam hormônios, usando um modelo de computador que pontua os cérebros em uma única escala de masculino a feminino. Concluiu que os cérebros das mulheres trans estavam deslocados do sexo de nascimento em direção à identidade de gênero.
• O estudo testou apenas uma diferença em uma direção. Testando ambas as direções, como é habitual, a principal diferença entre mulheres trans e homens fica mais fraca. Ajustando pelo fato de terem sido feitas três comparações, poderia facilmente ser acaso.
• A diferença maior entre mulheres trans e mulheres ainda se manteria após esses ajustes. Portanto, a disputa é sobre se os cérebros das mulheres trans diferem dos dos homens, não se diferem dos das mulheres.
• Com apenas 24 pessoas por grupo, o tamanho de qualquer diferença é instável. Um resultado incomum no grupo dos homens nunca foi verificado refazendo a análise sem ele.
• O teste usado pelo estudo para justificar seu método estatístico é fraco com grupos tão pequenos. Os críticos dizem que métodos que fazem menos suposições deveriam ao menos ter sido relatados também.
• Das 24 mulheres trans, 6 sentiam atração por homens e 18 por mulheres. A orientação sexual está ligada à estrutura cerebral, e os autores originais tinham esses dados, mas não os levaram em conta.
• Cada crítico pediu repetidamente os dados originais e não obteve resposta, por isso a crítica se baseia em números publicados. Pedem que os dados sejam divulgados e o estudo repetido por outros.

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.