Informant ratings of cognitive decline in old age: Validation against change on cognitive tests over 7 to 8 years

Background. Informant questionnaires on cognitive decline are increasingly used as screening tests for dementia. Informants can provide a longitudinal perspective that is not possible with cognitive screening tests administered at one point in time. However, there are limited data on the validity of such questionnaires when judged against longitudinal change on cognitive tests. Methods. A community sample of elderly people aged ≥ 70 was assessed on cognitive tests at baseline and after a follow-up of 7-8 years. The participants were given the Mini-Mental State Examination and tests of episodic memory and mental speed. At follow-up, the short-form of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) was completed by informants for 287 of the participants. Results. Elderly people who were rated by informants as having moderate or severe decline had declined significantly on cognitive tests. The IQCODE correlated as highly with cognitive test change scores as these change scores correlated with each other. Conclusions. The IQCODE is a valid way of assessing cognitive decline when assessment can be carried out only at one point in time.