Subtle changes in Sir Terry Pratchett's use of language in his books anticipated his dementia diagnosis by almost ten years, research has shown.
The study, from academics at Cardiff University, Loughborough University and the University of Oxford, used computer software to analyse the range of nouns and adjectives used in 33 of his best-selling Discworld novels.
The results show a significant decrease in the diversity of nouns and adjectives in his later works,. This shift was particularly marked in the diversity of adjectives, which decreased below a defined threshold approximately ten years before Pratchett's formal diagnosis.
Sir Terry Pratchett died in 2015 at the age of 66. He had posterior cortical atrophy, a rare form of early-onset Alzheimer's disease that primarily affects visual processing.
Study co-author Dr Melody Pattison, based at Cardiff University's School of English, Communication and Philosophy, said: "Our analysis of Sir Terry Pratchett's novels suggests that subtle changes in linguistic patterns, such as decreased lexical diversity, may precede clinical diagnosis of dementia by a considerable margin. In particular we found the richness of descriptive language in his books gradually narrowed."
We would normally expect less lexical diversity as texts get longer, but even after controlling for text length our findings were still significant. This was not something a reader would necessarily notice, but rather a subtle, progressive change.
Dr Thom Wilcockson, from Loughborough's School of Sport, Exercise and Health Sciences, who led the study, said: "Identifying dementia in the early stages is important as it may enable us to use interventions sooner before the brain is damaged beyond repair.
"Research indicates that memory problems may not be the first symptom of dementia. We wanted to explore whether language could be an early warning sign, and to do this, we used Sir Terry Pratchett's books, who himself suffered dementia.
"Our analysis found that Sir Terry's use of language did indeed change during his career. These results suggest that language may be one of the first signs of dementia, and Sir Terry's books reveal a potential new approach for early diagnosis."
The study, Detecting Dementia Using Lexical Analysis: Terry Pratchett's Discworld Tells a More Personal Story, is published in Brain Sciences and can be viewed here.
