The Claus Case: Exploring the Use of Propositional Idea Density for Alzheimer Detection
Low linguistic ability has been associated with low cognitive reserve, which might result in the development of Alzheimer’s disease. As a result, propositional idea density (PID), as a measure of linguistic ability in early life, might predict cognitive decline in late life. This paper explores the differences in propositional behavior between healthy individuals and Alzheimer’s patients, using a newly developed computerized propositional idea density measure for Dutch texts. This exploratory study describes an experiment on literary text. We measured the propositional idea density of the works of one author without Alzheimer’s disease (i.e. Elsschot) and one author with attested Alzheimer’s disease (i.e. Claus). Changes in propositional idea density for both authors were compared, as well as the differences in propositional idea density in early life. Analyses from this experiment showed that the propositional idea density in early life of Elsschot was not significantly higher than that of Claus. The propositional idea density of Elsschot significantly increased over time. This change in propositional idea density greatly differed from the slight decrease in propositional idea density of Claus. On the one hand, this study fails to support the hypothesis that a low propositional idea density in early life predicts cognitive decline in late life. On the other hand, the results provide support to the hypothesis that a slight decrease in propositional idea density over time might be a predictor of cognitive decline in late life. However, much more research is needed to corroborate these findings. The propositional idea density software for Dutch is available on request.