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年の研究は、男性24人、女性24人、まだホルモンを使っていないトランスジェンダー女性24人を、脳を男性から女性までの1つの尺度で採点するコンピューターモデルで比較しました。トランス女性の脳は、生まれつきの性別から性自認の方へずれていると結論づけました。
• その研究は、一方向の違いだけを検定しました。通常どおり両方向を検定すると、トランス女性と男性の重要な違いは弱くなります。3つの比較が行われたことを調整すると、偶然でも十分に起こりえます。
• トランス女性と女性の間のより大きな違いは、これらの調整の後も成り立ちます。したがって、争点は、トランス女性の脳が女性の脳と異なるかではなく、男性の脳と異なるかどうかです。
• 各グループが24人だけでは、違いの大きさは不安定です。男性のグループにある1つの異常な結果は、それを除いて分析をやり直して確認されることはありませんでした。
• この研究が統計手法を正当化するために使った検定は、これほど小さなグループでは弱いものです。批判者は、仮定の少ない方法も少なくとも報告されるべきだったと述べています。
• トランス女性24人のうち、6人は男性に、18人は女性に惹かれていました。性的指向は脳の構造と関連しており、元の著者はこのデータを持っていたのに、考慮に入れませんでした。
• 批判者それぞれが元のデータを繰り返し請求しましたが、返答はなく、そのため批判は公表された数字に頼っています。データの公開と、他の研究者による研究の再現を求めています。

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.