Cognitive impairment in the elderly--a community survey.

Previous studies have suggested that up to a fifth of people over the age of 80 years may suffer severe dementia-like illnesses. This total population survey of over a thousand people over the age of 75 suggests that the prevalence of marked cognitive impairment is much less than expected. However, differences in the age structure, representativeness, response rates and size of the samples surveyed, together with differences in methods of measurement, make comparison between studies difficult.