Delving into ChatGPT usage in academic writing through excess vocabulary

Large language models (LLMs) like ChatGPT can generate and revise text with human-level performance. These models come with clear limitations: they can produce inaccurate information, reinforce existing biases, and be easily misused. Yet, many scientists use them for their scholarly writing. But how wide-spread is such LLM usage in the academic literature? To answer this question, we present an unbiased, large-scale approach: we study vocabulary changes in 14 million PubMed abstracts from 2010--2024, and show how the appearance of LLMs led to an abrupt increase in the frequency of certain style words. This excess word analysis suggests that at least 10% of 2024 abstracts were processed with LLMs. This lower bound differed across disciplines, countries, and journals, reaching 30% for some sub-corpora. We show that LLMs have had an unprecedented impact on the scientific literature, surpassing the effect of major world events such as the Covid pandemic.