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

• 2022 年的研究比較了 24 名男性、24 名女性和 24 名尚未使用荷爾蒙的跨性別女性，使用一個將大腦在單一男性到女性量表上評分的電腦模型。它的結論是，跨性別女性的大腦已偏離其出生性別，朝向她們的性別認同。
• 該研究只檢驗了單一方向的差異。若像通常那樣檢驗兩個方向，跨性別女性與男性之間的關鍵差異就變弱。考慮到做了三次比較而調整後，很容易只是偶然。
• 跨性別女性與女性之間較大的差異，在這些調整後仍然成立。因此爭議在於跨性別女性的大腦是否與男性不同，而不是是否與女性不同。
• 每組只有 24 人，任何差異的大小都不穩定。男性組中有一個不尋常的結果，但從未排除它再重新分析以檢查。
• 該研究用來為其統計方法辯護的檢定，在這麼小的組別下很薄弱。批評者表示，至少也應該報告假設較少的方法。
• 24 名跨性別女性中，6 人被男性吸引，18 人被女性吸引。性傾向與大腦結構有關，而原作者有這項資料，卻沒有納入考慮。
• 每位批評者都多次索取原始資料而沒有得到回覆，因此批評依賴已發表的圖表。他們呼籲公開資料，並由他人重複這項研究。

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.