Vocabulary Changes in Agatha Christie's Mysteries as an Indication of Dementia: A Case Study

Although the novelist Agatha Christie was never diagnosed with dementia, it is believed to have been the cause of her decline in her later years. We analyzed the vocabulary size, the repeated use of fixed phrases, and the indefinite noun usage in 16 Agatha Christie novels written between ages 28 and 82. We found statistically significant drops in vocabulary, and increases in repeated phrases and indefinite nouns in 15 detective novels from The Mysterious Affair at Styles to Postern of Fate. These language effects are recognized as symptoms of memory difficulties associated with Alzheimer’s disease. Our study supports the conclusion that Agatha Christie’s last few novels show early signs of encroaching dementia. Changes in Agatha Christie’s writing are consistent not with normal aging but with Alzheimer’s disease. Bottom line 6. Discussion • A sharp vocabulary drop, and a sharp increase in repeating phrases (where tested texts are of the same genre) and a sharp increase in indefinite-word usage suggest that Agatha Christie suffered from Alzheimer’s disease. • These signs, especially indefinite-word usage, are present in her writing from her early 70s. • Our results support Garrard et al.’s (2005) conclusion, based on their smaller study of three novels by Iris Murdoch (diagnosed with AD), that non-invasive text analysis can detect the onset of dementia “before anyone [has] the remotest suspicion of any untoward intellectual decline”. 5. An outlier: Christie’s thriller • Passenger to Frankfurt — thriller, not detective novel. ‣ Written in her early to mid-70s, published at age 79. • Outlier: ‣ In phrase repetition; ‣ In vocabulary size; ‣ Largest vocabulary of all novels analyzed: Draws on vocabulary of much political commentary read by Christie in research for the novel. • Not an outlier in use of indefinite words. • Demonstrates limitations of measures dependent on nature or genre of content, advantages of content-independent measures. B A