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

Vocabulary Changes in Agatha Christie’s Mysteries as an Indication of Dementia:
A Case Study
Ian Lancashire* and Graeme Hirst†
University of Toronto, *Department of English and †Department of Computer Science
Ian.Lancashire, Graeme.Hirst
Alzheimer’s disease leads to changes in language production at all levels — lexical, syn-
tactic, and discourse — that are different to or markedly greater than those observed in
normal aging (Maxim & Bryan 1994). For example, whereas “the lexicon continues to
expand indefinitely until death or illness intervenes”, the “semantic and then
phonological output lexicon” becomes progressively “inaccessible” in Alzheimer’s dis-
ease (Maxim & Bryan 1994: 3, 24). And while in healthy aging, semantic retrieval speed
deteriorates and hence “the number of ‘indefinite’ words may increase” (Maxim & Bryan
1994: 46), as may the number of repeated phrases, Nicholas et al. (1985) demonstrated
that both indefinite words and repetitions occur significantly more often in the language
of Alzheimer’s patients than in that of healthy people of similar age and level of educa-
These facts suggest that an assessment of dementia might be based in part on an analysis
of a diachronic corpus of writing by the patient. Garrard et al. (2005) compared three
works by the British novelist Iris Murdoch, whose diagnosis of Alzheimer’s disease was
confirmed post mortem. Her final novel, which was written during her decline, had a
much smaller vocabulary than novels from her early and middle years. In addition, a
small sample suggested that her sentences were syntactically simpler.
Here, we analyze the vocabulary of the British mystery writer Agatha Christie, who, al-
though never diagnosed, was also believed to have suffered from dementia in her final
years even as she continued to write. Our analysis, on a much larger and more-
representative corpus than that which Garrard et al. used, concentrates on vocabulary-
richness measures and opens a project that will also look at syntactic and discourse-level
aspects of her texts.
Agatha Christie (1890–1976), in a 53-year writing career, crafted about 85 novels and
plays. Bodley Head published her first novel, The Mysterious Affair at Styles, in 1920,
and Collins her last, Postern of Fate, in 1973. The public had bought 400 million copies
of her works by 1975 and 2 billion by 1990. Her typical detective novel gives readers a
Presented at the 19th Annual Rotman Research Institute Conference, Cognitive Aging: Research and Prac-
tice, 8–10 March 2009, Toronto,
problem to be solved. Conversational dialogue and spare narration carry the reader along.
She provides clues and diversions and maintains suspense until her sleuth unveils a usu-
ally elusive solution that ends the book. Her novels each contain between 55,000 and
75,000 words. Her custom, until the last books, was to work out the plot meticulously
beforehand in a notebook, and to write the last chapter—where her detective laid out the
solution—first. Her notes on Lord Edgeware Dies and Evil under the Sun “are almost
identical to the finished article” (Thompson 2007: 369).
Janet Morgan, a biographer trusted by the Christie family, says that after Elephants can
Remember, written when Christie was 81, “her powers really declined” (Morgan 1984:
370). When subsequently writing Postern of Fate, she reportedly found it “harder than
ever to concentrate”: this last book “nearly killed her” (Morgan 1984: 371). Her preoc-
cupation with old people and their memories in both Elephants can Remember and Pos-
tern of Fate reflects more on her personal circumstances than on crime, murderer, and
clues. Readers have complained about inconsistencies in character and plotting in both
these late works. Much of Postern digresses into Christie’s past memories and current
problems, and the murderer is an afterthought. Her agent directed her to editorial help,
and her husband Max and her secretary, Mrs Daphne Honeybone, “tidied it up”:
Christie’s daughter Rosalind then asked Collins “to press for no more books”. Morgan
concluded, “Physical and mental decline is sad” (pp. 371–72). By the time of Elephants
can Remember, Christie had aged considerably, having fallen and broken a hip (Thomp-
son 2007: 464, 473–74). Four years later, friends reported her thin and “frail”; she had
angry fits (in one she cut off all her hair) and did not always make sense in conversation
(Thompson 2007: 483). Although she was never assessed for dementia, her last novels
reveal an inability to create a crime solvable by clue-detection according to the rules of
the genre that she helped to create.
Material and Methods
Fourteen Christie novels written between ages 34 and 82 were digitized, and digitized
copies of her first two mysteries, The Mysterious Affair at Styles (age 28) and The Secret
Adversary (age 32), were taken from Project Gutenberg. After all punctuation, apostro-
phes, and hyphens were deleted, each text was divided into 10,000-word segments. The
segments were then analyzed with the software tools Concordance and the Text Analysis
Computing Tools (TACT).
We performed three analyses of the first 50,000 words of each novel:
1. Like Garrard et al. (2005), as a simple measure of vocabulary size and richness,
we counted the number of different words used.
2. As a second measure of vocabulary richness, we counted the number of different
maximal phrase-types (i.e., word n-grams) that were repeated. These are defined
by word-length and frequency. For example, if in a given text we saw 5 occur-
rences of “all sorts of things” and 7 occurrences of both “all sorts of” and “all
sorts”, we would count this as two repeated phrase-types, not three, because all
occurrences of “all sorts” are contained in the longer phrases.
3. We counted the number of occurrences of the vague, indefinite words “thing”,
“anything”, and “something”.
Table 1 displays total counts for vocabulary size and repeating phrases, and the percent-
age of words that are indefinite nouns in the first 50,000 words of each novel.
Age at com-
words (%)
Towards Zero
*A thriller (not a mystery) that was written with the help of book research.
Table 1. Counts for vocabulary (word-types) and repeating phrases, and per-
centages of indefinite nouns in the first 50,000 words of 16 Christie novels.
Vocabulary size. The richness of the vocabulary of Christie’s novels declines with her
age at composition. The three novels that she wrote in her 80s, Nemesis, Elephants, and
Postern, have a smaller vocabulary than any of the analyzed works written by her be-
tween ages 28 to 63. Word-types in the first 50,000 words of her novels fall by one-fifth
between ages 28–32 and 81–82. Elephants Can Remember, written when she was 81,
exhibits a staggering drop in vocabulary, almost 31%, compared with Destination Un-
known, written 18 years earlier. Some 15,000 words shorter than Nemesis and Postern of
Fate, which preceded and followed it, Elephants appears to register the onset of a pro-
found writing block. Possibly Christie’s broken hip, the year before, was a factor. A lin-
ear regression on the decline in vocabulary with age approaches significance [F(1,14) =
3.95, p = .066], and is highly significant when the outlier, Frankfurt, is removed (see dis-
cussion below) [F(1,13) = 9.80, p < .01].
Repeated phrases. The number of different repeating phrase-types in the first 50,000
words in Christie’s novels increases with age, again implying a decline in the lexical rich-
ness of her writing. The increase with age approaches significance [F(1,14) = 4.06, p
= .064], and again is highly significant when the outlier, Frankfurt, is removed [F(1,13) =
8.47, p < .015].
Indefinite words. Christie’s use of vague, indefinite “thing” words increases signifi-
cantly with age from 0.27% of her word-count in Styles (1920) to 1.23% in Postern
(1973) [F(1,14) = 22.6, p < .0005]. Frankfurt is not an outlier in these data, and exclud-
ing it makes very little difference to the analysis.
Her family’s testimony about Christie’s otherwise undiagnosed physical and mental de-
cline offers an explanation for these data: encroaching dementia, as in the case of the
English novelist Iris Murdoch that Garrard et al. (2005) studied. Our analysis suggests,
in addition, that repeating phrases and, in particular, indefinite-term usage (not used by
Garrard et al.) are significant markers.
Outlier. Passenger to Frankfurt has the largest vocabulary of all the works we analyzed.
Unlike Christie’s other works, it is a thriller, not a detective mystery, conceived, written,
and researched in her early to mid 70s. Subtitled “An extravaganza”, it draws on books
by political thinkers that she requested of her publishers. On receiving her manuscript,
they were doubtful about bringing it out because it differed so much from her detective
fiction. Much of the vocabulary in Passenger to Frankfurt comes from her reliance on
these sources. We therefore exclude it as an outlier from our tests for vocabulary rich-
ness. Nonetheless, we observe that it was not an outlier with regard to indefinite words.
Ongoing work. We will next analyze Christie’s texts for known syntactic and discourse-
level characteristics of Alzheimer’s language. For comparison, we will also carry out
parallel analyses of the works of several writers who are not suspected of dementia in old
While few present-day patients have a large online diachronic corpus available for analy-
sis, this will begin to change as more individuals begin to keep, if only by inertia, a life-
time archive of e-mail, blogs, professional documents, and the like. While the diversity
of topics and genres in such an archive brings methodological problems to the analysis
(as observed with literary genre in Passenger to Frankfurt), we can nonetheless foresee
the possibility of automated textual analysis as a part of the early diagnosis of Alz-
heimer’s disease and similar dementias.
Garrard, P., Maloney, L.M., Hodges, J. R., & Patterson, K. (2005). The effects of very
early Alzheimer’s disease on the characteristics of writing by a renowned author. Brain,
128.2, 250–60.
Maxim, J. & Bryan, K. (1994). Language of the Elderly: A Clinical Perspective. Lon-
don: Whurr.
Nicholas, M., Obler, L. K., Albert, M. L., Helm-Estabrooks, N. (1985). Empty speech in
Alzheimer’s disease and fluent aphasia. Journal of Speech and Hearing Research, 28:
Morgan, J. (1984). Agatha Christie: A Biography. London: Collins.
Thompson, L. (2007). Agatha Christie: An English Mystery. London: Headline Review.
... We draw on a number of recent articles on Iris Murdoch and Alzheimer's disease progression (Garrard, Maloney, Hodges, & Patterson, 2005;Hirst & Wei Feng, 2012;Lancashire & Hirst, 2009;Le, Lancashire, Hirst, & Jokel, 2011;Pakhomov, Chacon, Wicklund, & Gundel, 2011;van Velzen, Nanetti, & de Deyn, 2014). Garrard et al. (2005) were also instrumental in highlighting Alzheimer's disease through changes in writing and used a different approach, which included other elements of language (nouns, verbs, adverbs and adjectives and function words, e.g. ...
... As Ahmed, Haigh, de Jager, and Garrard (2013) and Ferguson, Spencer, Craig, and Colyvas (2014) point out; the study of the subtle language changes over the lifespan of wellknown writers (Lancashire, 2010), including Iris Murdoch and Agatha Christie (e.g. Garrard et al., 2005;Lancashire & Hirst, 2009;Le, 2010;Le et al., 2011;Van Velzen & Garrard, 2008) and political figures (Garrard, 2009) has highlighted that Alzheimer's disease may be apparent years or even decades anyone becomes aware of any symptoms of cognitive deterioration. AD is apparent through lexical repetition and is marked by smaller, higher frequency vocabulary and lower use of Function Words over Content Words (Bird, Ralph, Patterson, & Hodges, 2000;Garrard et al., 2005). ...
... When looking at the results of the RPAS visualization, a number of points can be made. Overall, Iris Murdoch used fewer unique words and had more repetition than P.D. James, which is an indicator for dementia and Alzheimer's disease (Bird et al., 2000;Garrard et al., 2005;Lancashire & Hirst, 2009). P.D. James used more consistently male gendered pronouns in all her novels (~80%), and it didn't matter whether the main character was Adam Dalgliesh or Cordelia Grey (see B5, B9). ...
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Using data containing stylometric markers for depression and Alzheimer’s disease, the 45 novels of Iris Murdoch and P.D. James are examined to see if a signature of an individual, their personality, changes over time due to life events and natural ageing. We use variants of the critical slowing down 1-lag autocorrelation and coefficient of skewness techniques with a multivariate identity measure, RPAS to visualize these changes. We find that life events such as depression, anxiety, and Alzheimer’s disease might be identified outside of natural ageing through a tipping point phenomenon. We believe these techniques might be a useful self-help tool to aid in the signalling of depressive episodes, such as averting suicide, and the early identification of Alzheimer’s disease, or for law enforcement personnel monitoring terrorists on watch lists.
... Diary deficits included lower idea density (a measure of information relevant to number of words) and some aspects of lower grammatical complexity. They also cohere with studies of the novelist Iris Murdoch, reporting that linguistic properties of her later novels, prior to but closest in time to her AD diagnosis, revealed certain properties of linguistic decline as compared with her earlier novels, for example, vocabulary range reduction (Garrard et al., 2005; see also Lancashire & Hirst, 2009;Le et al., 2011 ). ...
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Purpose This research investigated the nature of cognitive decline in prodromal Alzheimer's disease (AD), particularly in mild cognitive impairment, amnestic type (aMCI). We assessed language in aMCI as compared with healthy aging (HA) and healthy young (HY) with new psycholinguistic assessment of complex sentences, and we tested the degree to which deficits on this language measure relate to performance in other general cognitive domains such as memory. Method Sixty-one individuals with aMCI were compared with 24 HA and 10 HY adults on a psycholinguistic measure of complex sentence production (relative clauses). In addition, HA, HY, and a subset of the aMCI participants ( n = 22) were also tested on a multidomain cognitive screen, the Addenbrooke's Cognitive Examination–Revised (ACE-R), and on a verbal working memory Brown–Peterson (BP) test. General and generalized linear mixed models were used to test psycholinguistic results and to test whether ACE-R and BP performance predicted performance on the psycholinguistic test similarly in the aMCI and HA groups. Results On the psycholinguistic measure, sentence imitation was significantly deficited in aMCI in comparison with that in HA and HY. Experimental factorial designs revealed that individuals with aMCI had particular difficulty repeating sentences that especially challenged syntax–semantics integration. As expected, the aMCI group also performed significantly below the HY and HA groups on the ACE-R. Neither the ACE-R Memory subtest nor the BP total scores predicted performance on the psycholinguistic task for either the aMCI or the HA group. However, the ACE-R total score significantly predicted psycholinguistic task performance, with increased ACE-R performance predicting increased psycholinguistic task performance only for the HA group, not for the aMCI group. Conclusions Results suggest a selective deterioration in language in aMCI, specifically a weakening of syntax–semantics integration in complex sentence processing, and a general independence of this language deficit and memory decline. Results cohere with previous assessments of the nature of difficulty in complex sentence formation in aMCI. We argue that clinical screening for prodromal AD can be strengthened by supplementary testing of language, as well as memory, and extended evaluation of strength of their relation.
... Mild cognitive impairment (MCI) is a condition that is regarded as a stage preceding dementia (Reisberg & Gauthier 2008). Linguistic analysis has shown great potential in identifying early signs of dementia, since the disorder negatively affects language production at all levels (Lancashire & Hirst 2009). Although linguistic features are more successful in identifying persons with clinically manifest dementia than persons with MCI (see e.g. ...
... Masrani et al. [17] were able to show that language declines as well. Lancashire et al. [20] researched the possibility of approaching Alzheimer's of the writer Agatha Christie by analyzing novels written at different life stages from age 34 to 82. The first 50,000 words of included novels were inquired with a tool named TACT, which operates comparable to LIWC (shown in Section 3) and showed a decline in language complexity and diversity. ...
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A connection between language and psychology of natural language processing for predicting psychological traits (NLPsych) is apparent and holds great potential for accessing the psyche, understand cognitive processes and detect mental health conditions. However, results of works in this field that we call NLPsych could be further improved and is sparse and fragmented, even though approaches and findings often are alike. This survey collects such research and summarizes approaches, data sources, utilized tools and methods, as well as findings. Approaches of included work can roughly be divided into two main strands: word-list-based inquiries and data-driven research. Some findings show that the change of language can indicate the course of mental health diseases, subsequent academic success can be predicted by the use of function words and dream narratives show highly complex cognitive processes – to name but a few. By surveying results of included work, we draw the ‘bigger picture’ that in order to grasp someone’s psyche, it is more important to research how people express themselves rather than what they say, which surfaces in function words. Furthermore, often research unawarely induce biases that worsen results, thus leading to the conclusion that future research should rather focus on data-driven approaches rather than hand-crafted attempts.
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Der Beitrag gilt einer bestimmten Perspektive auf die Digital Humanities. Dazu wird die Geschichte der Philologie als Bezugspunkt gewählt, um das sperrige Verhältnis von Gegenstand und technischer Methode zu schärfen. Unter der Formel Virtual Humanities sollen Zugriffsweisen und Methoden auf kulturwissenschaftliche Inhalte gefasst werden, mit denen das Potenzial der DH erweitert wird. Diese Ergänzung zielt auf Wissensformen, Methoden und Praxeologien, die ein Moment der Eigenständigkeit der Gegenstände betonen. Phänomene, die wie die Resultate von Data-Mining weniger durch hermeneutische Kompetenz, sondern die im Zuge technischer Prozessualität emergieren. Die neuen Wissensformen, die zu Foucaults Konzept eines positiven Unbewussten des Wissens in Bezug gesetzt werden, stellen bei aller Emergenz und Technizität zugleich neue Anforderungen an die Betreiberinnen. Der Umgang mit großen Datenmassen erfordert neuen Fertigkeiten des Sehens, der Umgang mit virtuellen Gegenständen neue Formen einer geschickten, einer körpernahen Praxeologie. Die Entwicklung wird vor dem Hintergrund einer Lage verortet, die durch Begriffe wie Post- und Transhumanismus sowie nach einem Bestreben um artenübergreifende Kommunikation und Kollaboration gekennzeichnet ist. Die Virtual Humanities werden zur Herausforderung neuer Wissensformen und ihrer Institutionalisierung in einer Universität der Zukunft.
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Literary studies continues to have a penchant for great men. In 2015, for example, 20% of authors listed as subjects in the MLA International Bibliography accounted for just under 60% of all articles or book chapters published that year. Just the top 1% of authors, or 33 in total, accounted for 1,302 works, or 20.8% of the total. Four of these authors were women, and one was not white (W. E. B. Du Bois). Those numbers are even slightly more concentrated than in 1970, when 1% of authors accounted for 15.9% of all articles and book chapters. In that year, only one of the most frequently mentioned authors was a woman (George Eliot), and all were white.
The present study discusses the relevance of measures of lexical diversity (LD) to the assessment of learner corpora. It also argues that existing measures of LD, many of which have become specialized for use with language corpora, are fundamentally measures of lexical repetition, are based on an etic perspective of language, and lack construct validity. The proposed solution draws from Zipf’s (1935) emic perspective of language, which views LD as a matter of perception, but which also assumes that competent speakers of a common language share similar perceptions. The present study tests whether this is true and specifically whether untrained human raters will show high levels of inter-rater reliability in their judgments of the levels of LD found in 60 texts extracted from a corpus of narratives written in English by a mix of language learners and native speakers. The results confirm Zipf’s assertion, but also indicate that a relatively large number of motivated raters are needed to demonstrate this tendency. The remainder of the study discusses the implications these results have for the development of an automated measure of LD to be used with learner corpora. The proposed method begins with human judgments of a representative subsample of a corpus, proceeds to a statistical model of objective measures that accurately predicts the human judgments, and ends with a multidimensional, corpus-specific automated measure that outputs reliable estimates of how a reliable group of human judges would rate the levels of LD in the texts of that corpus.
Authorship attribution is an active research direction due to its legal and financial importance. Its goal is to identify the authorship from the anonymous texts. In this paper, we propose a Topic Drift Model (TDM), which can monitor the dynamicity of authors' writing styles and learn authors' interests simultaneously. Unlike previous authorship attribution approaches, our model is sensitive to the temporal information and the ordering of words. Thus it can extract more information from texts. The experimental results show that our model achieves better results than other models in terms of accuracy. We also demonstrate the potential of our model to address the authorship verification problem.
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Iris Murdoch (I.M.) was among the most celebrated British writers of the postwar era. Her final novel, however, received a less than enthusiastic critical response on its publication in 1995. Not long afterwards, I.M. began to show signs of insidious cognitive decline, and received a diagnosis of Alzheimer's disease, which was confirmed histologically after her death in 1999. Anecdotal evidence , as well as the natural history of the condition, would suggest that the changes of Alzheimer's disease were already established in I.M. while she was writing her final work. The end product was unlikely, however, to have been influenced by the compensatory use of dictionaries or thesauri, let alone by later editorial interference. These facts present a unique opportunity to examine the effects of the early stages of Alzheimer's disease on spontaneous written output from an individual with exceptional expertise in this area. Techniques of automated textual analysis were used to obtain detailed comparisons among three of her novels: her first published work, a work written during the prime of her creative life and the final novel. Whilst there were few disparities at the levels of overall structure and syntax, measures of lexical diversity and the lexical characteristics of these three texts varied markedly and in a consistent fashion. This unique set of findings is discussed in the context of the debate as to whether syntax and semantics decline separately or in parallel in patients with Alzheimer's disease.
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Fourteen measures of empty speech during a picture description task were examined in four subject groups--patients with Alzheimer's dementia, Wernicke's aphasias, anomic aphasias, and normal controls--to discover if these groups could be distinguished on the basis of their discourse. Patients with Alzheimer's dementia were distinguished from patients with Wernicke's aphasia by producing more empty phrases and conjunctions, whereas patients with Wernicke's aphasia produced more neologisms, and verbal and literal paraphasias. The demented patients shared many empty speech characteristics with patients with anomic aphasia. Naming deficits, as measured by confrontation naming tasks, did not correlate with empty discourse production. Our findings may be useful clinically for distinguishing these different patient groups.
Agatha Christie: An English Mystery
  • L Thompson
Thompson, L. (2007). Agatha Christie: An English Mystery. London: Headline Review.
Agatha Christie: A Biography
  • J Morgan
Morgan, J. (1984). Agatha Christie: A Biography. London: Collins.
Language of the Elderly: A Clinical Perspective
  • J Maxim
  • K Bryan
Maxim, J. & Bryan, K. (1994). Language of the Elderly: A Clinical Perspective. London: Whurr.