Use of some vocabulary shows the state of mind of the writer!

Famous mystery novelist Agatha Christie suffered from Alzheimer's. Two Toronto university professors have finally proved what many biographers of the world's top mystery novelist have hinted at - that she suffered from mental illness. This research by professors Ian Lancashire and Graeme Hirst on Christie's mental illness has landed them the top spot in the New York Times 9th Annual Year in Ideas. Lancashire, a professor of English & Hirst, a computer scientist, have combined humanities and science to give conclusive proof of Christie's Alzheimer's related dementia during the final years of her life. As part of their research, the two professors degitised 14 of her novels and used textual analysis software to determine the richness and size of the vocabulary used, as well as phrases often repeated and an increase in the use of infinite words, an indicator of the disease.
Their research showed that her final two books use a much smaller vocabulary than her earlier works, with differences as large as 31%. Her other later works compared with her last two volumes also show a much richer vocabulary.