Background. We report on the change in cognitive function in a population sample of elderly people who have been examined on two occasions more than 3 years apart.
Methods. A sample of 1135 persons aged 70–102 years was interviewed at base-line then reinterviewed 3·6 years later with the Canberra Interview for the Elderly, which included tests of episodic memory and cognitive speed as well as the Mini-Mental State Examination and the National Adult Reading Test (NART).
Results. Mortality and loss to follow-up reduced the sample to 736, of whom 614 completed at least one test of cognitive performance on both occasions. Cognitive performance decreased with age, except on the NART. Decline over the follow-up period increased as a function of age in all cognitive measures, except the NART. Change in cognitive scores was close to normal distribution. Incident dementia was associated strongly with age and current level of cognitive performance, but not with rate of decline. Cognitive decline and the risk of incident dementia did not differ by gender.
Conclusions. A score indicating possible impairment in the very elderly carries a worse prognosis than for the younger elderly. Decline is almost universal in at least one cognitive area among those over the age of 85.