Terry Pratchett's writing showed early signs of dementia, study suggests

A study published in the journal Brain Sciences suggests that lexical analysis of Terry Pratchett’s Discworld novels could have identified signs of dementia nearly a decade before his formal diagnosis. Researchers from Cardiff University, Loughborough University, and Oxford University analyzed 33 of the author's novels using the type-token ratio to measure lexical diversity.

The study found that the diversity of nouns and adjectives dropped significantly in later works. Specifically, adjective diversity fell below a defined threshold starting with 'The Last Continent', published in 1998—approximately nine and a half years before Pratchett announced his diagnosis of a rare form of early-onset Alzheimer's in 2007.

The researchers noted that the change was not due to Pratchett using fewer adjectives, but rather a tendency to reuse the same adjectives as his books grew longer. Pratchett, who became a prominent advocate for dementia research in Britain, passed away in 2015.