ABSTRACT
Because of the nature of dementias and neuropsychiatric disorders, it is highly desirable (if not essential) to have the perspective of a reliable informant in assessing cognition. Moreover, dementia involves a deterioration or decline in cognitive ability from a premorbid level (Jorm and Jacomb, 1989). Because there is a risk of both false-positive and false-negative assessments based on premorbid IQ and education, it is necessary to have an estimate of the premorbid level of cognitive ability. Individuals who have always been limited in intellectual ability may be falsely diagnosed as demented while highly intelligent and educated individuals could be misclassified as intact despite the fact that they have sustained a substantial cognitive decline (Jorm and Jacomb, 1989). Cognitive decline was estimated by using informants who had knowledge of the subject’s premorbid level of functioning and behavior. Informant reports were postulated to have greater validity, because their observations were based on the performance on independent activities of daily living rather than investigator-initiated cognitive tests.
