Nature Human Behaviour Study Measures a 21–50% Drop in Writing-Complexity Variance From LLM Assistance

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A study now published in Nature Human Behaviour (the journal version of arXiv 2502.11266) covers three studies, seven datasets and more than 880,000 texts, and finds LLM writing assistance cuts writing-complexity variance by a statistically significant 21–50% across datasets and models. LLM polishing systematically strips textual cues to gender, age, ideology and moral values, amplifying dominant patterns and suppressing others; the authors observed variance in complexity dropping across social media, news and scientific writing after ChatGPT's release. The concrete risk they name is that language-based assessment in psychology, mental health care and recruitment becomes less reliable once the input has been homogenized.