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年的研究比较了24名男性、24名女性和24名尚未使用激素的跨性别女性，使用的计算机模型将大脑在一个从男性到女性的单一量表上打分。它得出结论认为，跨性别女性的大脑从其出生性别向其性别认同方向偏移。
• 该研究只检验了单一方向的差异。像通常那样检验两个方向，会使跨性别女性与男性之间的关键差异变弱。考虑到进行了三项比较后进行调整，它很可能是偶然的。
• 跨性别女性与女性之间更大的差异在这些调整后仍然成立。因此，争议在于跨性别女性的大脑是否与男性不同，而不是是否与女性不同。
• 每组只有24人，任何差异的大小都不稳定。男性组中的一个异常结果从未通过去掉它重新运行分析来检查。
• 研究用来证明其统计方法合理的检验，在这么小的组别中很薄弱。批评者说，至少也应报告假设较少的方法。
• 24名跨性别女性中，6人被男性吸引，18人被女性吸引。性取向与大脑结构有关，原作者有这些数据却没有考虑。
• 每位批评者都多次索要原始数据却没有得到回复，因此批评依赖已发表的数字。他们呼吁公开数据，并由其他人重复该研究。

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.