Did Agatha's shrinking vocab signal dementia?

A compelling new study reported in the Vancouver Sun suggests that the novels Agatha Christie wrote late in life reflect the onset of dementia. Researchers cite her shrinking vocabulary and rather dazed wanderings-off from the plot. Maybe, maybe not. But our vote for best Agatha is the bone-chilling Sad Cypress, written when she was still spry and middle-aged. A young woman named Elinor is found guilty of murdering a fluffy blonde and condemned to be hanged. The situation seems so hopeless you really don't see how diabolical Agatha will save her ... We dare you to white-knuckle your way through this one.